linux 驱动之LCD驱动(有framebuffer)

<简介>

LCD驱动里有个很重要的概念叫帧缓冲(framebuffer)，它是Linux系统为显示设备提供的一个接口，应用程序在图形模式允许对显示缓冲区进行读写操作。用户根本不用关心物理显示缓冲区的具体位置及存放方式，因为这些都由缓冲区设备驱动完成了。

启动开发板后执行ls /dev/fb* 命令可以看到，帧缓冲设备的主设备号为29，对应/dev/fbn设备文件，一般为/dev/fb0

在弄清楚LCD驱动架构之前，我们先弄清楚几个重要的结构体，为了减短篇幅，有一些不是很重要的成员会用省略，具体的源代码请大家参考Linux源代码，这里我使用的源代码是天嵌公司提供的移植好的Linux-2.6.30.4。

a:内核中结构fb_info

fb_info结构体（在include/linux/fb.h文件里定义）

struct fb_info {
int node; /* 序号索引值，/dev/fb0，/dev/fb1 其中0,1 就是从这里获得的*/
int flags;
struct mutex lock;/* 一般在 open/release/ioctl 函数里会用到的锁 */
struct fb_var_screeninfo var;/* 可变参数，很重要 */
struct fb_fix_screeninfo fix; /* 固定参数，很重要 */
struct fb_monspecs monspecs;/* Current Monitor specs */
struct work_struct queue; /* Framebuffer event queue */
struct fb_pixmap pixmap; /* Image hardware mapper */
struct fb_pixmap sprite; /* Cursor hardware mapper */
struct fb_cmap cmap; /* Current cmap */
struct list_head modelist; /* mode list */
struct fb_videomode *mode;/* current mode */

。。。。。。

struct fb_ops *fbops;
struct device *device;/* This is the parent */
struct device *dev;/* This is this fb device */

。。。。。。
char __iomem *screen_base;/* "显存“的基地址 */
unsigned long screen_size; /* ”显存“的大小 */
void *pseudo_palette; /* 16位假的调色板 */
#define FBINFO_STATE_RUNNING0
#define FBINFO_STATE_SUSPENDED1
u32 state; /* Hardware state i.e suspend */
void *fbcon_par; /* fbcon use-only private area */
/* From here on everything is device dependent */
void *par; /* 这个用来存放私有数据 */
};

a:内核数据结构

fb_ops结构体（在include/linux/fb.h文件里定义）

考虑到fb_ops结构体里面的函数指针成员太多，这里仅简单列举几个比较常见的，具体的请参考源代码。

struct fb_ops{
struct module *owner; /* 模块计数 */
int (*fb_open)(struct fb_info *info, int user); /* 打开函数，第一个参数为fb_info */
int (*fb_release)(struct fb_info *info, int user);
。。。。。。
/* fb_check_var函数用来检查可变参数，并调整修改可变参数 */
int (*fb_check_var)(struct fb_var_screeninfo *var, struct fb_info *info);
。。。。。。
/*fb_setcolreg函数就是用来设置fb_info里面的pseudo_palette调色板成员 */
int (*fb_setcolreg)(unsigned regno, unsigned red, unsigned green,
unsigned blue, unsigned transp, struct fb_info *info);
。。。。。。

/* 下面三个是通用的函数 */
/* Draws a rectangle */
void (*fb_fillrect) (struct fb_info *info, const struct fb_fillrect *rect);
/* Copy data from area to another */
void (*fb_copyarea) (struct fb_info *info, const struct fb_copyarea *region);
/* Draws a image to the display */
void (*fb_imageblit) (struct fb_info *info, const struct fb_image *image);
。。。。。。
/* 有了fb_ioctl应用层可以通过ioctl系统调用来设置屏幕参数等 */
int (*fb_ioctl)(struct fb_info *info, unsigned int cmd,
unsigned long arg);
。。。。。。
/* 有了fb_mmap应用层可以通过mmap系统调用来读写帧缓冲区内存 */
int (*fb_mmap)(struct fb_info *info, struct vm_area_struct *vma);
。。。
};

a：内核中数据结构

fb_var_screeninfo 结构体（在include/linux/fb.h文件里定义）

fb_var_screeninfo 被fb_info结构体所包含，这个结构体主要用来设置LCD屏幕的参数，如分辨率、像素比特数等，LCD驱动程序里面硬件相关的设置很多都涉及这个结构体。

struct fb_var_screeninfo {
__u32 xres;/* visible resolution,分辨率，即一行有多少个点 */
__u32 yres;
__u32 xres_virtual;/* virtual resolution*/
__u32 yres_virtual;
__u32 xoffset;/* offset from virtual to visible */
__u32 yoffset;/* resolution*/

__u32 bits_per_pixel;/* guess what，定义每个点用多少个自己表示 */
__u32 grayscale;/* != 0 Graylevels instead of colors */

struct fb_bitfield red;/* bitfield in fb mem if true color, */
struct fb_bitfield green;/* else only length is significant */
struct fb_bitfield blue;
struct fb_bitfield transp;/* transparency*/

__u32 nonstd; /* != 0 Non standard pixel format */

__u32 activate;/* see FB_ACTIVATE_**/

__u32 height;/* height of picture in mm */
__u32 width;/* width of picture in mm */

__u32 accel_flags;/* (OBSOLETE) see fb_info.flags */

/* Timing: All values in pixclocks, except pixclock (of course) */
__u32 pixclock;/* pixel clock in ps (pico seconds) */
__u32 left_margin;/* time from sync to picture*/
__u32 right_margin;/* time from picture to sync*/
__u32 upper_margin;/* time from sync to picture*/
__u32 lower_margin;
__u32 hsync_len;/* length of horizontal sync*/
__u32 vsync_len;/* length of vertical sync*/
__u32 sync; /* see FB_SYNC_**/
__u32 vmode; /* see FB_VMODE_**/
__u32 rotate; /* angle we rotate counter clockwise */
__u32 reserved[5];/* Reserved for future compatibility */
};

a:内核数据结构

fb_fix_screeninfo 结构体（在include/linux/fb.h文件里定义）

struct fb_fix_screeninfo {
char id[16];/* 驱动名字就保存在这里*/
unsigned long smem_start; /* fb缓冲区的基地址，这是一个物理地址 */
__u32 smem_len; /* fb缓冲区的长度 */
__u32 type; /* FB_TYPE_类型*/
__u32 type_aux;/* Interleave for interleaved Planes */
__u32 visual;/* FB_VISUAL_类型*/
__u16 xpanstep;/* 一般设置为0 */
__u16 ypanstep;/* 一般设置为0 */
__u16 ywrapstep;/* 一般设置为0 */
__u32 line_length;/* 屏幕一行有多个字节 */
unsigned long mmio_start;/* Start of Memory Mapped I/O */
/* (physical address) */
__u32 mmio_len;/* Length of Memory Mapped I/O */
__u32 accel; /* Indicate to driver which*/
/* specific chip/card we have*/
__u16 reserved[3];/* Reserved for future compatibility */
};

<LCD驱动实例一>

我们的mini2440使用的是X35的LCD屏，根据X35的LCD说明文档，需要在BSP中X35LCD屏的一些参数。

在mach-mini2440.c中添加X35LCD的参数

#if defined(CONFIG_FB_S3C2410_X240320) //定义X35LCD参数

#define LCD_WIDTH 240 //屏宽

#define LCD_HEIGHT 320 //屏高

#define LCD_PIXCLOCK 170000 //时钟

#define LCD_RIGHT_MARGIN 25 //左边界

#define LCD_LEFT_MARGIN 0 //右边界

#define LCD_HSYNC_LEN 4 //行同步

#define LCD_UPPER_MARGIN 0 //上边界

#define LCD_LOWER_MARGIN 4 //下边界

#define LCD_VSYNC_LEN 9 //帧同步

#elif //定义其他LCD屏参数

#endif

好了，我们现在发现要想上面定义的X35LCD的参数正在起作用，必须使得CONFIG_FB_S3C2410_X240320=y；我们需要在/driver/video/Kconfig中定义

config FB_S3C2410_X240320

boolean "3.5 inch 240X320 LCD(ACX502BMU)"

depends on FB_S3C2410

help

3.5 inch 240X320 LCD(ACX502BMU)

然后我们通过make menuconfig选中"3.5 inch 240X320 LCD(ACX502BMU)"这一选项。

根据我们的X35LCD屏的说明文档，我们已经定义了一些边界参数和同步参数，因为我们的LCD驱动是基于platform总线的，所以需要在这个BSP中添加LCD的平台设备。

struct platform_device s3c_device_lcd = { //添加LCD平台设备

.name = "s3c2410-lcd", //设备名

.id = -1,

.num_resources = ARRAY_SIZE(s3c_lcd_resource),

.resource = s3c_lcd_resource, //资源

.dev = {

.dma_mask = &s3c_device_lcd_dmamask,

.coherent_dma_mask = 0xffffffffUL

}

};

资源的定义如下

static struct resource s3c_lcd_resource[] = {

[0] = { //内存空间资源

.start = S3C24XX_PA_LCD,

.end = S3C24XX_PA_LCD + S3C24XX_SZ_LCD - 1,

.flags = IORESOURCE_MEM,

},

[1] = { //中断资源

.start = IRQ_LCD,

.end = IRQ_LCD,

.flags = IORESOURCE_IRQ,

}

};

然后我们把s3c_device_lcd放到mini2440_devices[]结构体中，接着调用platform_add_devices(mini2440_devices, ARRAY_SIZE(mini2440_devices))将LCD平台设备注册到内核。

对于我们的LCD，需要给这个平台设备添加平台设备数据，通过调用

s3c24xx_fb_set_platdata(&mini2440_fb_info);

static struct s3c2410fb_mach_info mini2440_fb_info __initdata = {

.displays = &mini2440_lcd_cfg, //定义s3c2410fb_display数据

.num_displays = 1,

.default_display = 0,

.gpccon = 0xaa955699, //GPC端口设置

.gpccon_mask = 0xffc003cc,

.gpcup = 0x0000ffff,

.gpcup_mask = 0xffffffff,

.gpdcon = 0xaa95aaa1, //GPD端口设置

.gpdcon_mask = 0xffc0fff0,

.gpdup = 0x0000faff,

.gpdup_mask = 0xffffffff,

.lpcsel = 0xf82,

};

继续看

static struct s3c2410fb_display mini2440_lcd_cfg __initdata = {

#if !defined (LCD_CON5)

.lcdcon5 = S3C2410_LCDCON5_FRM565 |

S3C2410_LCDCON5_INVVLINE |

S3C2410_LCDCON5_INVVFRAME |

S3C2410_LCDCON5_PWREN |

S3C2410_LCDCON5_HWSWP,

#else

.lcdcon5 = LCD_CON5,

#endif

.type = S3C2410_LCDCON1_TFT, //屏的类型

.width = LCD_WIDTH, //屏宽

.height = LCD_HEIGHT, //屏高

.pixclock = LCD_PIXCLOCK, //时钟

.xres = LCD_WIDTH, //水平分辨率

.yres = LCD_HEIGHT, //垂直分辨率

.bpp = 16, //每个像素的比特数

.left_margin = LCD_LEFT_MARGIN + 1, //左边界

.right_margin = LCD_RIGHT_MARGIN + 1, //右边界

.hsync_len = LCD_HSYNC_LEN + 1, //行同步

.upper_margin = LCD_UPPER_MARGIN + 1, //上边界

.lower_margin = LCD_LOWER_MARGIN + 1, //下边界

.vsync_len = LCD_VSYNC_LEN + 1, //帧同步

};

好了，这样我们就完成了LCD驱动的移植工作，接着我们通过make menuconfig选择相应的文件层、设备层和X35LCD屏这个三个选项，最后编译生成内核。

三．LCD文件层和驱动层设计思路

LCD驱动可以分为文件层和设备层，文件层又叫FrameBuffer设备驱动，对应的文件是fbmem.c，主要实现为用户提供file_operations接口，同时为设备层提供一些函数接口，这个帧缓冲设备驱动内核已经帮我们编写好，我们不需要编写。在设备层我们专门Mini2440的LCD编写的驱动在s3c2410fb.c中，该驱动叫LCD驱动，主要是填充一个fbinfo结构，然后用register_framebuffer注册到内核，对于fbinfo结构，最主要的是填充它的fs_ops成员。对于驱动工程师，第一件事就是学会根据LCD说明文档，移植LCD。第二件事就是会写设备层LCD驱动。

3.1 LCD驱动中几个重要的数据结构

在分析内核LCD驱动代码之前，我们先要熟悉几个结构体。

struct fb_info {

int node;

int flags;

struct mutex lock;

struct mutex mm_lock;

struct fb_var_screeninfo var; //当前缓冲区的可变参数

struct fb_fix_screeninfo fix; //当前缓冲区的固定参数

struct fb_monspecs monspecs;

struct work_struct queue;

struct fb_pixmap pixmap;

struct fb_pixmap sprite;

struct fb_cmap cmap; //当前的调试板

struct list_head modelist;

struct fb_videomode *mode;

#ifdef CONFIG_FB_BACKLIGHT //背光

struct backlight_device *bl_dev;

struct mutex bl_curve_mutex; //背光灯层次

u8 bl_curve[FB_BACKLIGHT_LEVELS]; //调整背光灯

#endif

#ifdef CONFIG_FB_DEFERRED_IO

struct delayed_work deferred_work;

struct fb_deferred_io *fbdefio;

#endif

struct fb_ops *fbops; //帧缓冲操作函数集合

struct device *device;

struct device *dev;

int class_flag;

#ifdef CONFIG_FB_TILEBLITTING

struct fb_tile_ops *tileops;

#endif

char __iomem *screen_base; //虚拟基地址

unsigned long screen_size; //虚拟内存大小

void *pseudo_palette;

#define FBINFO_STATE_RUNNING 0

#define FBINFO_STATE_SUSPENDED 1

u32 state;

void *fbcon_par;

void *par; //私有数据

resource_size_t aperture_base;

resource_size_t aperture_size;

};

为了清晰起见，对于fb_info结构体，我只注释了重点几个成员，每个帧设备都有一个fb_info，该结构体包含了驱动实现的底层函数和记录设备状态的数据。fb_info结构体主要包含fb_var_screeninfo、fb_fix_screeninfo、fb_cmap和fb_ops，

struct fb_var_screeninfo {

__u32 xres; //水平分辨率

__u32 yres; //垂直分辨率

__u32 xres_virtual;

__u32 yres_virtual;

__u32 xoffset;

__u32 yoffset;

__u32 bits_per_pixel; //每个像素所占的比特数

__u32 grayscale;

struct fb_bitfield red;

struct fb_bitfield green;

struct fb_bitfield blue;

struct fb_bitfield transp;

__u32 nonstd;

__u32 activate;

__u32 height; //屏高

__u32 width; //屏宽

__u32 accel_flags;

__u32 pixclock; //像素时钟

__u32 left_margin; //左边界

__u32 right_margin; //右边界

__u32 upper_margin; //上边界

__u32 lower_margin; //下边界

__u32 hsync_len; //水平同步长度

__u32 vsync_len; //垂直同步长度

__u32 sync;

__u32 vmode;

__u32 rotate;

__u32 reserved[5];

};

上面的fb_var_screeninfo结构体存放了用户可以修改的显示控制器参数，如分辨率，BPP等参数。

struct fb_fix_screeninfo {

char id[16];

unsigned long smem_start; //fb缓冲区开始的位置

__u32 smem_len; //fb缓冲区长度

__u32 type;

__u32 type_aux;

__u32 visual; //屏幕色彩模式

__u16 xpanstep;

__u16 ypanstep;

__u16 ywrapstep;

__u32 line_length;

unsigned long mmio_start; //内存映射开始位置

__u32 mmio_len; //内存映射长度

__u32 accel;

__u16 reserved[3];

};

上面这个fb_fix_screeninfo主要记录了用户不能修改的固定显示控制器参数，如缓冲区物理地址、缓冲区长度、显示色彩模式、内核映射的开始位置等，这些结构体程序都需要驱动程序初始化时设置。

struct fb_cmap {

__u32 start; //颜色板的第一个元素入口位置

__u32 len; //元素长度

__u16 *red; //红

__u16 *green; //绿

__u16 *blue; //蓝

__u16 *transp; //透明分量值

};

对于上面的fb_cmap，它主要记录了一个颜色板信息，用户空间可以使用ioctl函数的FBIOGETCMAP和FBIOPUTCMAP读取和设置颜色表的值。

struct fb_ops {

struct module *owner;

int (*fb_open)(struct fb_info *info, int user);

int (*fb_release)(struct fb_info *info, int user);

ssize_t (*fb_read)(struct fb_info *info, char __user *buf,

size_t count, loff_t *ppos);

ssize_t (*fb_write)(struct fb_info *info, const char __user *buf,

size_t count, loff_t *ppos);

int (*fb_check_var)(struct fb_var_screeninfo *var, struct fb_info *info);

int (*fb_set_par)(struct fb_info *info);

int (*fb_setcolreg)(unsigned regno, unsigned red, unsigned green,

unsigned blue, unsigned transp, struct fb_info *info);

int (*fb_setcmap)(struct fb_cmap *cmap, struct fb_info *info);

int (*fb_blank)(int blank, struct fb_info *info);

int (*fb_pan_display)(struct fb_var_screeninfo *var, struct fb_info *info);

void (*fb_fillrect) (struct fb_info *info, const struct fb_fillrect *rect);

void (*fb_copyarea) (struct fb_info *info, const struct fb_copyarea *region);

void (*fb_imageblit) (struct fb_info *info, const struct fb_image *image);

int (*fb_cursor) (struct fb_info *info, struct fb_cursor *cursor);

void (*fb_rotate)(struct fb_info *info, int angle);

int (*fb_sync)(struct fb_info *info);

int (*fb_ioctl)(struct fb_info *info, unsigned int cmd,

unsigned long arg);

int (*fb_compat_ioctl)(struct fb_info *info, unsigned cmd,

unsigned long arg);

int (*fb_mmap)(struct fb_info *info, struct vm_area_struct *vma);

void (*fb_get_caps)(struct fb_info *info, struct fb_blit_caps *caps,

struct fb_var_screeninfo *var);

void (*fb_destroy)(struct fb_info *info);

};

其中fb_ops就是用来实现对帧缓冲设备的操作。

3.2 LCD驱动层

好了，我们先看看驱动层代码s3c2410fb.c

static struct platform_driver s3c2410fb_driver = {

.probe = s3c2410fb_probe, //探测

.remove = s3c2410fb_remove, //移除

.suspend = s3c2410fb_suspend, //挂起

.resume = s3c2410fb_resume, //恢复

.driver = {

.name = "s3c2410-lcd", //驱动名

.owner = THIS_MODULE,

},

};

我们看看探测函数s3c2410fb_probe

static int __init s3c2410fb_probe(struct platform_device *pdev)

{

return s3c24xxfb_probe(pdev, DRV_S3C2410);

}

继续看

static int __init s3c24xxfb_probe(struct platform_device *pdev,

enum s3c_drv_type drv_type)

{

struct s3c2410fb_info *info; //该驱动的全局变量结构体

struct s3c2410fb_display *display; //LCD屏的配置信息

struct fb_info *fbinfo; //帧缓冲驱动中对应的fb_info结构体

struct s3c2410fb_mach_info *mach_info; //内核平台设备数据

struct resource *res; //LCD资源

int ret;

int irq;

int i;

int size;

u32 lcdcon1;

mach_info = pdev->dev.platform_data; //获得平台设备数据

if (mach_info == NULL) {

dev_err(&pdev->dev,

"no platform data for lcd, cannot attach ");

return -EINVAL;

}

if (mach_info->default_display >= mach_info->num_displays) {

dev_err(&pdev->dev, "default is %d but only %d displays ",

mach_info->default_display, mach_info->num_displays);

return -EINVAL;

}

//获得LCD配置信息结构体

display = mach_info->displays + mach_info->default_display;

irq = platform_get_irq(pdev, 0); //获得中断号

if (irq < 0) {

dev_err(&pdev->dev, "no irq for device ");

return -ENOENT;

}

//给帧缓冲fb_info分配空间，并将struct s3c2410fb_info作为其私有数据

fbinfo = framebuffer_alloc(sizeof(struct s3c2410fb_info), &pdev->dev);

if (!fbinfo)

return -ENOMEM;

platform_set_drvdata(pdev, fbinfo); //把fb_info作为平台设备的私有数据

info = fbinfo->par; //获得fb_info的私有数据

info->dev = &pdev->dev;

info->drv_type = drv_type;

res = platform_get_resource(pdev, IORESOURCE_MEM, 0);//获取资源

if (res == NULL) {

dev_err(&pdev->dev, "failed to get memory registers ");

ret = -ENXIO;

goto dealloc_fb;

}

size = (res->end - res->start) + 1;

info->mem = request_mem_region(res->start, size, pdev->name); //申请内存

if (info->mem == NULL) {

dev_err(&pdev->dev, "failed to get memory region ");

ret = -ENOENT;

goto dealloc_fb;

}

info->io = ioremap(res->start, size); //物理地址转换为虚拟地址

if (info->io == NULL) {

dev_err(&pdev->dev, "ioremap() of registers failed ");

ret = -ENXIO;

goto release_mem;

}

info->irq_base = info->io + ((drv_type == DRV_S3C2412) ? S3C2412_LCDINTBASE : S3C2410_LCDINTBASE); //基地址

dprintk("devinit ");

strcpy(fbinfo->fix.id, driver_name); //驱动名

lcdcon1 = readl(info->io + S3C2410_LCDCON1);

writel(lcdcon1 & ~S3C2410_LCDCON1_ENVID, info->io + S3C2410_LCDCON1); //禁止输出使能

fbinfo->fix.type = FB_TYPE_PACKED_PIXELS;

fbinfo->fix.type_aux = 0; //LCD屏固定参数设置

fbinfo->fix.xpanstep = 0;

fbinfo->fix.ypanstep = 0;

fbinfo->fix.ywrapstep = 0;

fbinfo->fix.accel = FB_ACCEL_NONE;

fbinfo->var.nonstd = 0; //LCD屏可变参数设置

fbinfo->var.activate = FB_ACTIVATE_NOW;

fbinfo->var.accel_flags = 0;

fbinfo->var.vmode = FB_VMODE_NONINTERLACED;

fbinfo->fbops = &s3c2410fb_ops; //操作函数集合

fbinfo->flags = FBINFO_FLAG_DEFAULT;

fbinfo->pseudo_palette = &info->pseudo_pal;

for (i = 0; i < 256; i++)

info->palette_buffer[i] = PALETTE_BUFF_CLEAR;//初始化调试板为空

ret = request_irq(irq, s3c2410fb_irq, IRQF_DISABLED, pdev->name, info);

if (ret) {

dev_err(&pdev->dev, "cannot get irq %d - err %d ", irq, ret);

ret = -EBUSY;

goto release_regs;

}

info->clk = clk_get(NULL, "lcd"); //获取时钟

if (!info->clk || IS_ERR(info->clk)) {

printk(KERN_ERR "failed to get lcd clock source ");

ret = -ENOENT;

goto release_irq;

}

clk_enable(info->clk); //使能时钟

dprintk("got and enabled clock ");

msleep(1);

info->clk_rate = clk_get_rate(info->clk) //设置时钟;

for (i = 0; i < mach_info->num_displays; i++) { //获取最大需要的显存大小

unsigned long smem_len = mach_info->displays[i].xres;

smem_len *= mach_info->displays[i].yres;

smem_len *= mach_info->displays[i].bpp;

smem_len >>= 3;

if (fbinfo->fix.smem_len < smem_len)

fbinfo->fix.smem_len = smem_len;

}

//申请fb_info的显示缓冲区空间，并将其地址写入fbinfo中

ret = s3c2410fb_map_video_memory(fbinfo);

if (ret) {

printk(KERN_ERR "Failed to allocate video RAM: %d ", ret);

ret = -ENOMEM;

goto release_clock;

}

dprintk("got video memory ");

fbinfo->var.xres = display->xres; //水平分辨率

fbinfo->var.yres = display->yres; //垂直分辨率

fbinfo->var.bits_per_pixel = display->bpp; //每个像素的比特数

s3c2410fb_init_registers(fbinfo); //初始化GPIO寄存器

//检查fb_info->var与fbinfo支持的哪一种分辨率、色彩模式匹配

s3c2410fb_check_var(&fbinfo->var, fbinfo);

ret = s3c2410fb_cpufreq_register(info);

if (ret < 0) {

dev_err(&pdev->dev, "Failed to register cpufreq ");

goto free_video_memory;

}

ret = register_framebuffer(fbinfo);//注册帧缓冲设备fb_info到系统中

if (ret < 0) {

printk(KERN_ERR "Failed to register framebuffer device: %d ",

ret);

goto free_cpufreq;

}

ret = device_create_file(&pdev->dev, &dev_attr_debug);

if (ret) {

printk(KERN_ERR "failed to add debug attribute ");

}

printk(KERN_INFO "fb%d: %s frame buffer device ",

fbinfo->node, fbinfo->fix.id);

return 0;

free_cpufreq:

s3c2410fb_cpufreq_deregister(info);

free_video_memory:

s3c2410fb_unmap_video_memory(fbinfo);

release_clock:

clk_disable(info->clk);

clk_put(info->clk);

release_irq:

free_irq(irq, info);

release_regs:

iounmap(info->io);

release_mem:

release_resource(info->mem);

kfree(info->mem);

dealloc_fb:

platform_set_drvdata(pdev, NULL);

framebuffer_release(fbinfo);

return ret;

}

上面这个探测函数中包含了几个重要的函数，如申请帧缓冲设备的显存区空间的函数s3c2410fb_map_video_memory(fbinfo)；初始化GPIO寄存器的函数s3c2410fb_init_registers(fbinfo)；检查fb_info->var与fbinfo支持的哪一种分辨率、色彩模式匹配，并据此填充var中其他参数的函数s3c2410fb_check_var(&fbinfo->var, fbinfo)，下面我们依次对这三个函数进行分析。

首先看s3c2410fb_map_video_memory(fbinfo)，即申请帧缓冲设备的显存区空间的函数

static int __init s3c2410fb_map_video_memory(struct fb_info *info)

{

struct s3c2410fb_info *fbi = info->par; //获得fb_info的私有数据

dma_addr_t map_dma; //保存DMA缓冲区总线地址

unsigned map_size = PAGE_ALIGN(info->fix.smem_len);

dprintk("map_video_memory(fbi=%p) map_size %u ", fbi, map_size);

//将分配的一个写合并DMA缓存区设置为LCD屏幕的虚拟地址

info->screen_base = dma_alloc_writecombine(fbi->dev, map_size,

&map_dma, GFP_KERNEL);

if (info->screen_base) {

dprintk("map_video_memory: clear %p:%08x ",

info->screen_base, map_size);

memset(info->screen_base, 0x00, map_size); //设置DMA缓存内容为空

//将DMA缓冲区总线地址设为fb_info不可变参数中缓存的开始位置

info->fix.smem_start = map_dma;

dprintk("map_video_memory: dma=%08lx cpu=%p size=%08x ",

info->fix.smem_start, info->screen_base, map_size);

}

return info->screen_base ? 0 : -ENOMEM;

}

接着我们看看初始化GPIO寄存器的函数s3c2410fb_init_registers(fbinfo)

static int s3c2410fb_init_registers(struct fb_info *info)

{

struct s3c2410fb_info *fbi = info->par; //获得fb_info的私有数据

struct s3c2410fb_mach_info *mach_info = fbi->dev->platform_data;

unsigned long flags;

void __iomem *regs = fbi->io;

void __iomem *tpal;

void __iomem *lpcsel;

if (is_s3c2412(fbi)) {

tpal = regs + S3C2412_TPAL;

lpcsel = regs + S3C2412_TCONSEL;

} else {

tpal = regs + S3C2410_TPAL;

lpcsel = regs + S3C2410_LPCSEL;

}

local_irq_save(flags);

//把GPIO端口C和D配置成LCD模式

modify_gpio(S3C2410_GPCUP, mach_info->gpcup, mach_info->gpcup_mask);

modify_gpio(S3C2410_GPCCON, mach_info->gpccon, mach_info->gpccon_mask);

modify_gpio(S3C2410_GPDUP, mach_info->gpdup, mach_info->gpdup_mask);

modify_gpio(S3C2410_GPDCON, mach_info->gpdcon, mach_info->gpdcon_mask);

local_irq_restore(flags);

dprintk("LPCSEL = 0x%08lx ", mach_info->lpcsel);

writel(mach_info->lpcsel, lpcsel);

dprintk("replacing TPAL %08x ", readl(tpal));

writel(0x00, tpal);

return 0;

}

最后看看检查fb_info->var与fbinfo支持的哪一种分辨率、色彩模式匹配，并据此填充var中其他参数的函数s3c2410fb_check_var(&fbinfo->var, fbinfo)

static int s3c2410fb_check_var(struct fb_var_screeninfo *var,

struct fb_info *info)

{

struct s3c2410fb_info *fbi = info->par;

struct s3c2410fb_mach_info *mach_info = fbi->dev->platform_data;

struct s3c2410fb_display *display = NULL;

struct s3c2410fb_display *default_display = mach_info->displays +

mach_info->default_display;

int type = default_display->type; //获取LCD类型，TFT

unsigned i;

dprintk("check_var(var=%p, info=%p) ", var, info);

//验证x/y解析度

if (var->yres == default_display->yres &&

var->xres == default_display->xres &&

var->bits_per_pixel == default_display->bpp)

display = default_display;

else

for (i = 0; i < mach_info->num_displays; i++)

if (type == mach_info->displays[i].type &&

var->yres == mach_info->displays[i].yres &&

var->xres == mach_info->displays[i].xres &&

var->bits_per_pixel == mach_info->displays[i].bpp) {

display = mach_info->displays + i;

break;

}

if (!display) {

dprintk("wrong resolution or depth %dx%d at %d bpp ",

var->xres, var->yres, var->bits_per_pixel);

return -EINVAL;

}

var->xres_virtual = display->xres; //配置屏的虚拟解析像素

var->yres_virtual = display->yres;

var->height = display->height; //配置屏的高度宽度

var->width = display->width;

var->pixclock = display->pixclock; //配置屏的时钟

var->left_margin = display->left_margin; //配置屏的行帧同步、水平垂直同步

var->right_margin = display->right_margin;

var->upper_margin = display->upper_margin;

var->lower_margin = display->lower_margin;

var->vsync_len = display->vsync_len;

var->hsync_len = display->hsync_len;

fbi->regs.lcdcon5 = display->lcdcon5; ///配置LCD寄存器

fbi->regs.lcdcon1 = display->type;

var->transp.offset = 0; //配置透明度

var->transp.length = 0;

//根据BBP来设置可变参数RGB的颜色位域

switch (var->bits_per_pixel) {

case 1:

case 2:

case 4:

var->red.offset = 0;

var->red.length = var->bits_per_pixel;

var->green = var->red;

var->blue = var->red;

break;

case 8:

if (display->type != S3C2410_LCDCON1_TFT) {

var->red.length = 3;

var->red.offset = 5;

var->green.length = 3;

var->green.offset = 2;

var->blue.length = 2;

var->blue.offset = 0;

} else {

var->red.offset = 0;

var->red.length = 8;

var->green = var->red;

var->blue = var->red;

}

break;

case 12:

var->red.length = 4;

var->red.offset = 8;

var->green.length = 4;

var->green.offset = 4;

var->blue.length = 4;

var->blue.offset = 0;

break;

default:

case 16:

if (display->lcdcon5 & S3C2410_LCDCON5_FRM565) {

var->red.offset = 11; //偏移

var->green.offset = 5;

var->blue.offset = 0;

var->red.length = 5; //长度

var->green.length = 6;

var->blue.length = 5;

} else {

var->red.offset = 11;

var->green.offset = 6;

var->blue.offset = 1;

var->red.length = 5;

var->green.length = 5;

var->blue.length = 5;

}

break;

case 32:

var->red.length = 8;

var->red.offset = 16;

var->green.length = 8;

var->green.offset = 8;

var->blue.length = 8;

var->blue.offset = 0;

break;

}

return 0;

}

好了，我们已经分析完LCD驱动中probe探测函数了，该函数主要是分配fb_info结构体空间，然后填充fb_info，初始化GPIO控制器，检查并设置fb_info中可变参数，申请帧缓冲设备的显示缓冲区空间，最后调用register_framebuffer函数注册到内核。

下面我们把重点放在fb_info结构体的fb_ops成员上

static struct fb_ops s3c2410fb_ops = {

.owner = THIS_MODULE,

.fb_check_var = s3c2410fb_check_var, //检查参数

.fb_set_par = s3c2410fb_set_par, //激活fb_info参数配置

.fb_blank = s3c2410fb_blank, //显示空白

.fb_setcolreg = s3c2410fb_setcolreg, //设置颜色表

.fb_fillrect = cfb_fillrect, //可选

.fb_copyarea = cfb_copyarea, //可选

.fb_imageblit = cfb_imageblit, //可选

};

fp_ops是使得帧缓冲设备工作所需函数的集合，它们最终与LCD控制器打交道。

s3c2410fb_check_va用于调整可变参数，并修改为硬件所支持的值；s3c2410fb_set_par则根据屏幕参数设置具体读写LCD控制器的寄存器，使得LCD控制器进入相应的工作状态。对于fb_ops中的.fb_fillrect、fb_copyarea和fb_imageblit，我们通常使用通用的cfb_fillrect、cfb_copyarea和cfb_imageblit函数即可。s3c2410fb_setcolreg是用来实现伪颜色表和颜色表的填充。

对于fb_ops中的成员中s3c2410fb_check_va这个函数在上面probe探测函数中已经讲过了，剩下的任务就是分析下激活fb_info参数配置函数s3c2410fb_set_par和显示空白函数s3c2410fb_blank。

首先看看显示空白函数s3c2410fb_blank

static int s3c2410fb_blank(int blank_mode, struct fb_info *info)

{

struct s3c2410fb_info *fbi = info->par; //获得fb_info私有数据

void __iomem *tpal_reg = fbi->io; //获得内存指针

dprintk("blank(mode=%d, info=%p) ", blank_mode, info);

tpal_reg += is_s3c2412(fbi) ? S3C2412_TPAL : S3C2410_TPAL;

//根据显示空白的模式设置LCD开启或停止

if (blank_mode == FB_BLANK_POWERDOWN) {

s3c2410fb_lcd_enable(fbi, 0); //停止LCD

} else {

s3c2410fb_lcd_enable(fbi, 1); //开启LCD

}

//根据显示空白的模式控制临时调色板是否有效

if (blank_mode == FB_BLANK_UNBLANK)

writel(0x0, tpal_reg); //调色板寄存器无效

else {

dprintk("setting TPAL to output 0x000000 ");

writel(S3C2410_TPAL_EN, tpal_reg); //调色板寄存器有效

}

return 0;

}

跟踪s3c2410fb_blank中的s3c2410fb_lcd_enable函数

static void s3c2410fb_lcd_enable(struct s3c2410fb_info *fbi, int enable)

{

unsigned long flags;

local_irq_save(flags);

if (enable)

fbi->regs.lcdcon1 |= S3C2410_LCDCON1_ENVID; //开启LCD

else

fbi->regs.lcdcon1 &= ~S3C2410_LCDCON1_ENVID; //关闭LCD

writel(fbi->regs.lcdcon1, fbi->io + S3C2410_LCDCON1);

local_irq_restore(flags);

}

接着看看这个根据fbinfo->var激活fb_info中的参数配置函数s3c2410fb_set_par

static int s3c2410fb_set_par(struct fb_info *info)

{

struct fb_var_screeninfo *var = &info->var;

switch (var->bits_per_pixel) {//根据色位模式设置色彩模式

case 32:

case 16:

case 12:

info->fix.visual = FB_VISUAL_TRUECOLOR;

break;

case 1:

info->fix.visual = FB_VISUAL_MONO01;

break;

default:

info->fix.visual = FB_VISUAL_PSEUDOCOLOR;

break;

}

//设置fb_info中固定参数中一行的字节数

info->fix.line_length = (var->xres_virtual * var->bits_per_pixel) / 8;

s3c2410fb_activate_var(info); //激活fb_info参数配置

return 0;

}

我们看看s3c2410fb_set_par中激活fb_info参数配置函数s3c2410fb_activate_var

static void s3c2410fb_activate_var(struct fb_info *info)

{

struct s3c2410fb_info *fbi = info->par;

void __iomem *regs = fbi->io;

int type = fbi->regs.lcdcon1 & S3C2410_LCDCON1_TFT;

struct fb_var_screeninfo *var = &info->var;

int clkdiv;

//计算LCD控制器1中的CLKVAL值

clkdiv = DIV_ROUND_UP(s3c2410fb_calc_pixclk(fbi, var->pixclock), 2);

dprintk("%s: var->xres = %d ", __func__, var->xres);

dprintk("%s: var->yres = %d ", __func__, var->yres);

dprintk("%s: var->bpp = %d ", __func__, var->bits_per_pixel);

if (type == S3C2410_LCDCON1_TFT) { //配置TFT屏LCD控制寄存器

s3c2410fb_calculate_tft_lcd_regs(info, &fbi->regs);

--clkdiv;

if (clkdiv < 0)

clkdiv = 0;

} else { //配置STN屏LCD控制寄存器

s3c2410fb_calculate_stn_lcd_regs(info, &fbi->regs);

if (clkdiv < 2)

clkdiv = 2;

}

//设置LCD控制器1中的CLKVAL值

fbi->regs.lcdcon1 |= S3C2410_LCDCON1_CLKVAL(clkdiv);

dprintk("new register set: ");

dprintk("lcdcon[1] = 0x%08lx ", fbi->regs.lcdcon1);

dprintk("lcdcon[2] = 0x%08lx ", fbi->regs.lcdcon2);

dprintk("lcdcon[3] = 0x%08lx ", fbi->regs.lcdcon3);

dprintk("lcdcon[4] = 0x%08lx ", fbi->regs.lcdcon4);

dprintk("lcdcon[5] = 0x%08lx ", fbi->regs.lcdcon5);

//设置LCD控制器1-5的参数

writel(fbi->regs.lcdcon1 & ~S3C2410_LCDCON1_ENVID,

regs + S3C2410_LCDCON1);

writel(fbi->regs.lcdcon2, regs + S3C2410_LCDCON2);

writel(fbi->regs.lcdcon3, regs + S3C2410_LCDCON3);

writel(fbi->regs.lcdcon4, regs + S3C2410_LCDCON4);

writel(fbi->regs.lcdcon5, regs + S3C2410_LCDCON5);

s3c2410fb_set_lcdaddr(info); //设置帧缓冲起始地址寄存器1-3

fbi->regs.lcdcon1 |= S3C2410_LCDCON1_ENVID,

writel(fbi->regs.lcdcon1, regs + S3C2410_LCDCON1);

}

下面我们主要关注s3c2410fb_calculate_tft_lcd_regs和s3c2410fb_set_lcdaddr函数

static void s3c2410fb_calculate_tft_lcd_regs(const struct fb_info *info,

struct s3c2410fb_hw *regs)

{

const struct s3c2410fb_info *fbi = info->par;

const struct fb_var_screeninfo *var = &info->var;

switch (var->bits_per_pixel) {//根据色模式设置LCD控制器1和5

case 1:

regs->lcdcon1 |= S3C2410_LCDCON1_TFT1BPP;

break;

case 2:

regs->lcdcon1 |= S3C2410_LCDCON1_TFT2BPP;

break;

case 4:

regs->lcdcon1 |= S3C2410_LCDCON1_TFT4BPP;

break;

case 8:

regs->lcdcon1 |= S3C2410_LCDCON1_TFT8BPP;

regs->lcdcon5 |= S3C2410_LCDCON5_BSWP |

S3C2410_LCDCON5_FRM565;

regs->lcdcon5 &= ~S3C2410_LCDCON5_HWSWP;

break;

case 16:

regs->lcdcon1 |= S3C2410_LCDCON1_TFT16BPP;

regs->lcdcon5 &= ~S3C2410_LCDCON5_BSWP;

regs->lcdcon5 |= S3C2410_LCDCON5_HWSWP;

break;

case 32:

regs->lcdcon1 |= S3C2410_LCDCON1_TFT24BPP;

regs->lcdcon5 &= ~(S3C2410_LCDCON5_BSWP |

S3C2410_LCDCON5_HWSWP |

S3C2410_LCDCON5_BPP24BL);

break;

default:

dev_err(fbi->dev, "invalid bpp %d ",

var->bits_per_pixel);

}

dprintk("setting vert: up=%d, low=%d, sync=%d ",

var->upper_margin, var->lower_margin, var->vsync_len);

dprintk("setting horz: lft=%d, rt=%d, sync=%d ",

var->left_margin, var->right_margin, var->hsync_len);

//设置LCD控制器2、3、4

regs->lcdcon2 = S3C2410_LCDCON2_LINEVAL(var->yres - 1) |

S3C2410_LCDCON2_VBPD(var->upper_margin - 1) |

S3C2410_LCDCON2_VFPD(var->lower_margin - 1) |

S3C2410_LCDCON2_VSPW(var->vsync_len - 1);

regs->lcdcon3 = S3C2410_LCDCON3_HBPD(var->right_margin - 1) |

S3C2410_LCDCON3_HFPD(var->left_margin - 1) |

S3C2410_LCDCON3_HOZVAL(var->xres - 1);

regs->lcdcon4 = S3C2410_LCDCON4_HSPW(var->hsync_len - 1);

}

static void s3c2410fb_set_lcdaddr(struct fb_info *info)

{

unsigned long saddr1, saddr2, saddr3;

struct s3c2410fb_info *fbi = info->par;

void __iomem *regs = fbi->io;

saddr1 = info->fix.smem_start >> 1;

saddr2 = info->fix.smem_start;

saddr2 += info->fix.line_length * info->var.yres;

saddr2 >>= 1;

saddr3 = S3C2410_OFFSIZE(0) |

S3C2410_PAGEWIDTH((info->fix.line_length / 2) & 0x3ff);

dprintk("LCDSADDR1 = 0x%08lx ", saddr1);

dprintk("LCDSADDR2 = 0x%08lx ", saddr2);

dprintk("LCDSADDR3 = 0x%08lx ", saddr3);

//初始化LCD控制器的地址指针

writel(saddr1, regs + S3C2410_LCDSADDR1);

writel(saddr2, regs + S3C2410_LCDSADDR2);

writel(saddr3, regs + S3C2410_LCDSADDR3);

}

归纳下我们分析的这个激活fb_info参数配置函数s3c2410fb_activate_var，该函数主要是计算clkval的值，计算LCD控制器1-5的值，然后设置LCD控制器1-5，并设置帧缓冲寄存器。

<LCD驱动实例二>

#include <linux/kernel.h> #include <linux/module.h> #include <linux/errno.h> #include <linux/init.h> #include <linux/platform_device.h> #include <linux/dma-mapping.h> #include <linux/fb.h> #include <linux/clk.h> #include <linux/interrupt.h> #include <linux/mm.h>

#include <linux/slab.h> #include <linux/delay.h> #include <asm/irq.h> #include <asm/io.h> #include <asm/div64.h> #include <mach/regs-lcd.h> #include <mach/regs-gpio.h> #include <mach/fb.h> #include <linux/pm.h>

/*FrameBuffer设备名称*/
static char driver_name[] = "my2440_lcd";

/*定义一个结构体用来维护驱动程序中各函数中用到的变量
  先别看结构体要定义这些成员，到各函数使用的地方就明白了*/
struct my2440fb_var
{
    int lcd_irq_no;           /*保存LCD中断号*/
    struct clk *lcd_clock;    /*保存从平台时钟队列中获取的LCD时钟*/
    struct resource *lcd_mem; /*LCD的IO空间*/
    void __iomem *lcd_base;   /*LCD的IO空间映射到虚拟地址*/
    struct device *dev;

    struct s3c2410fb_hw regs; /*表示5个LCD配置寄存器，s3c2410fb_hw定义在mach-s3c2410/include/mach/fb.h中*/

    /*定义一个数组来充当调色板。
    据数据手册描述，TFT屏色位模式为8BPP时，调色板(颜色表)的长度为256，调色板起始地址为0x4D000400*/
    u32    palette_buffer[256];

    u32 pseudo_pal[16];
    unsigned int palette_ready; /*标识调色板是否准备好了*/
};

/*用做清空调色板(颜色表)*/
#define PALETTE_BUFF_CLEAR (0x80000000)

/*LCD平台驱动结构体，平台驱动结构体定义在platform_device.h中，该结构体成员接口函数在第②步中实现*/
static struct platform_driver lcd_fb_driver =
{
    .probe     = lcd_fb_probe,               /*FrameBuffer设备探测*/
    .remove    = __devexit_p(lcd_fb_remove), /*FrameBuffer设备移除*/
    .suspend   = lcd_fb_suspend,             /*FrameBuffer设备挂起*/
    .resume    = lcd_fb_resume,              /*FrameBuffer设备恢复*/
    .driver    =
    {
        /*注意这里的名称一定要和系统中定义平台设备的地方一致，这样才能把平台设备与该平台设备的驱动关联起来*/
        .name = "s3c2410-lcd",
        .owner = THIS_MODULE,
    },
};

static int __init lcd_init(void)
{
    /*在Linux中，帧缓冲设备被看做是平台设备，所以这里注册平台设备*/
    return platform_driver_register(&lcd_fb_driver);
}

static void __exit lcd_exit(void)
{
    /*注销平台设备*/
    platform_driver_unregister(&lcd_fb_driver);
}

module_init(lcd_init);
module_exit(lcd_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Huang Gang");
MODULE_DESCRIPTION("My2440 LCD FrameBuffer Driver");

②、LCD平台设备各接口函数的实现：

/*LCD FrameBuffer设备探测的实现，注意这里使用一个__devinit宏，到lcd_fb_remove接口函数实现的地方讲解*/ static int __devinit lcd_fb_probe(struct platform_device *pdev) { int i; int ret; struct resource *res; /*用来保存从LCD平台设备中获取的LCD资源*/ struct fb_info *fbinfo; /*FrameBuffer驱动所对应的fb_info结构体*/ struct s3c2410fb_mach_info *mach_info; /*保存从内核中获取的平台设备数据*/ struct my2440fb_var *fbvar; /*上面定义的驱动程序全局变量结构体*/ struct s3c2410fb_display *display; /*LCD屏的配置信息结构体，该结构体定义在mach-s3c2410/include/mach/fb.h中*/ /*获取LCD硬件相关信息数据，在前面讲过内核使用s3c24xx_fb_set_platdata函数将LCD的硬件相关信息保存到了LCD平台数据中，所以这里我们就从平台数据中取出来在驱动中使用*/ mach_info = pdev->dev.platform_data; if(mach_info == NULL) { /*判断获取数据是否成功*/ dev_err(&pdev->dev, "no platform data for lcd/n"); return -EINVAL; } /*获得在内核中定义的FrameBuffer平台设备的LCD配置信息结构体数据*/ display = mach_info->displays + mach_info->default_display;

/*给fb_info分配空间，大小为my2440fb_var结构的内存，framebuffer_alloc定义在fb.h中在fbsysfs.c中实现*/ fbinfo = framebuffer_alloc(sizeof(struct my2440fb_var), &pdev->dev); if(!fbinfo) { dev_err(&pdev->dev, "framebuffer alloc of registers failed/n"); ret = -ENOMEM; goto err_noirq; } platform_set_drvdata(pdev, fbinfo);/*重新将LCD平台设备数据设置为fbinfo，好在后面的一些函数中来使用*/ /*这里的用途其实就是将fb_info的成员par(注意是一个void类型的指针)指向这里的私有变量结构体fbvar，目的是到其他接口函数中再取出fb_info的成员par，从而能继续使用这里的私有变量*/ fbvar = fbinfo->par; fbvar->dev = &pdev->dev; /*在系统定义的LCD平台设备资源中获取LCD中断号,platform_get_irq定义在platform_device.h中*/ fbvar->lcd_irq_no = platform_get_irq(pdev, 0); if(fbvar->lcd_irq_no < 0) { /*判断获取中断号是否成功*/ dev_err(&pdev->dev, "no lcd irq for platform/n"); return -ENOENT; } /*获取LCD平台设备所使用的IO端口资源，注意这个IORESOURCE_MEM标志和LCD平台设备定义中的一致*/ res = platform_get_resource(pdev, IORESOURCE_MEM, 0); if(res == NULL) { /*判断获取资源是否成功*/ dev_err(&pdev->dev, "failed to get memory region resource/n"); return -ENOENT; } /*申请LCD IO端口所占用的IO空间(注意理解IO空间和内存空间的区别),request_mem_region定义在ioport.h中*/ fbvar->lcd_mem = request_mem_region(res->start, res->end - res->start + 1,pdev->name); if(fbvar->lcd_mem == NULL) { /*判断申请IO空间是否成功*/ dev_err(&pdev->dev, "failed to reserve memory region/n"); return -ENOENT; } /*将LCD的IO端口占用的这段IO空间映射到内存的虚拟地址，ioremap定义在io.h中注意：IO空间要映射后才能使用，以后对虚拟地址的操作就是对IO空间的操作*/ fbvar->lcd_base = ioremap(res->start, res->end - res->start + 1); if(fbvar->lcd_base == NULL) { /*判断映射虚拟地址是否成功*/ dev_err(&pdev->dev, "ioremap() of registers failed/n"); ret = -EINVAL; goto err_nomem; } /*从平台时钟队列中获取LCD的时钟，这里为什么要取得这个时钟，从LCD屏的时序图上看，各种控制信号的延迟都跟LCD的时钟有关。系统的一些时钟定义在arch/arm/plat-s3c24xx/s3c2410-clock.c中*/ fbvar->lcd_clock = clk_get(NULL, "lcd"); if(!fbvar->lcd_clock) { /*判断获取时钟是否成功*/ dev_err(&pdev->dev, "failed to find lcd clock source/n"); ret = -ENOENT; goto err_nomap; } /*时钟获取后要使能后才可以使用，clk_enable定义在arch/arm/plat-s3c/clock.c中*/ clk_enable(fbvar->lcd_clock); /*申请LCD中断服务，上面获取的中断号lcd_fb_irq，使用快速中断方式:IRQF_DISABLED 中断服务程序为:lcd_fb_irq，将LCD平台设备pdev做参数传递过去了*/ ret = request_irq(fbvar->lcd_irq_no, lcd_fb_irq, IRQF_DISABLED, pdev->name,fbvar); if(ret) { /*判断申请中断服务是否成功*/ dev_err(&pdev->dev, "IRQ%d error %d/n", fbvar->lcd_irq_no, ret); ret = -EBUSY; goto err_noclk; } /*好了，以上是对要使用的资源进行了获取和设置。下面就开始初始化填充fb_info结构体*/ /*首先初始化fb_info中代表LCD固定参数的结构体fb_fix_screeninfo*/ /*像素值与显示内存的映射关系有5种，定义在fb.h中。现在采用FB_TYPE_PACKED_PIXELS方式，在该方式下，像素值与内存直接对应，比如在显示内存某单元写入一个"1"时，该单元对应的像素值也将是"1"，这使得应用层把显示内存映射到用户空间变得非常方便。Linux中当LCD为TFT屏时，显示驱动管理显示内存就是基于这种方式*/ strcpy(fbinfo->fix.id, driver_name);/*字符串形式的标识符*/ fbinfo->fix.type = FB_TYPE_PACKED_PIXELS; fbinfo->fix.type_aux = 0;/*以下这些根据fb_fix_screeninfo定义中的描述，当没有硬件是都设为0*/ fbinfo->fix.xpanstep = 0; fbinfo->fix.ypanstep = 0; fbinfo->fix.ywrapstep= 0; fbinfo->fix.accel = FB_ACCEL_NONE;

fbinfo

    for (i = 0; i < mach_info->num_displays; i++) /*fb缓存的长度*/
    {
        /*计算FrameBuffer缓存的最大大小，这里右移3位(即除以8)是因为色位模式BPP是以位为单位*/
        unsigned long smem_len = (mach_info->displays[i].xres * mach_info->displays[i].yres * mach_info->displays[i].bpp) >> 3;

        if(fbinfo->fix.smem_len < smem_len)
        {
            fbinfo->fix.smem_len = smem_len;
        }
    }

    /*初始化LCD控制器之前要延迟一段时间*/
    msleep(1);

    /*初始化完fb_info后，开始对LCD各寄存器进行初始化，其定义在后面讲到*/
    my2440fb_init_registers(fbinfo);

    /*初始化完寄存器后，开始检查fb_info中的可变参数，其定义在后面讲到*/
    my2440fb_check_var(fbinfo);

    /*申请帧缓冲设备fb_info的显示缓冲区空间，其定义在后面讲到*/
    ret = my2440fb_map_video_memory(fbinfo);
    if (ret)
    {
        dev_err(&pdev->dev, "failed to allocate video RAM: %d/n", ret);
        ret = -ENOMEM;
        goto err_nofb;
    }

    /*最后，注册这个帧缓冲设备fb_info到系统中, register_framebuffer定义在fb.h中在fbmem.c中实现*/
    ret = register_framebuffer(fbinfo);
    if (ret < 0)
    {
        dev_err(&pdev->dev, "failed to register framebuffer device: %d/n",ret);
        goto err_video_nomem;
    }

    /*对设备文件系统的支持(对设备文件系统的理解请参阅：嵌入式Linux之我行——设备文件系统剖析与使用)
     创建frambuffer设备文件，device_create_file定义在linux/device.h中*/
    ret = device_create_file(&pdev->dev, &dev_attr_debug);
    if (ret)
    {
        dev_err(&pdev->dev, "failed to add debug attribute/n");
    }

    return 0;

/*以下是上面错误处理的跳转点*/
err_nomem:
    release_resource(fbvar->lcd_mem);
    kfree(fbvar->lcd_mem);

err_nomap:
    iounmap(fbvar->lcd_base);

err_noclk:
    clk_disable(fbvar->lcd_clock);
    clk_put(fbvar->lcd_clock);

err_noirq:
    free_irq(fbvar->lcd_irq_no, fbvar);

err_nofb:
    platform_set_drvdata(pdev, NULL);
    framebuffer_release(fbinfo);

err_video_nomem:
    my2440fb_unmap_video_memory(fbinfo);

    return ret;
}

/*LCD中断服务程序*/
static irqreturn_t lcd_fb_irq(int irq, void *dev_id)
{
    struct my2440fb_var    *fbvar = dev_id;
    void __iomem *lcd_irq_base;
    unsigned long lcdirq;

    /*LCD中断挂起寄存器基地址*/
    lcd_irq_base = fbvar->lcd_base + S3C2410_LCDINTBASE;

    /*读取LCD中断挂起寄存器的值*/
    lcdirq = readl(lcd_irq_base + S3C24XX_LCDINTPND);

    /*判断是否为中断挂起状态*/
    if(lcdirq & S3C2410_LCDINT_FRSYNC)
    {
        /*填充调色板*/
        if (fbvar->palette_ready)
        {
            my2440fb_write_palette(fbvar);
        }

        /*设置帧已插入中断请求*/
        writel(S3C2410_LCDINT_FRSYNC, lcd_irq_base + S3C24XX_LCDINTPND);
        writel(S3C2410_LCDINT_FRSYNC, lcd_irq_base + S3C24XX_LCDSRCPND);
    }

    return IRQ_HANDLED;
}

/*填充调色板*/
static void my2440fb_write_palette(struct my2440fb_var *fbvar)
{
    unsigned int i;
    void __iomem *regs = fbvar->lcd_base;

    fbvar->palette_ready = 0;

    for (i = 0; i < 256; i++)
    {
        unsigned long ent = fbvar->palette_buffer[i];

        if (ent == PALETTE_BUFF_CLEAR)
        {
            continue;
        }

        writel(ent, regs + S3C2410_TFTPAL(i));

        if (readw(regs + S3C2410_TFTPAL(i)) == ent)
        {
            fbvar->palette_buffer[i] = PALETTE_BUFF_CLEAR;
        }
        else
        {
            fbvar->palette_ready = 1;
        }
    }
}

/*LCD各寄存器进行初始化*/
static int my2440fb_init_registers(struct fb_info *fbinfo)
{
    unsigned long flags;
    void __iomem *tpal;
    void __iomem *lpcsel;

    /*从lcd_fb_probe探测函数设置的私有变量结构体中再获得LCD相关信息的数据*/
    struct my2440fb_var    *fbvar = fbinfo->par;
    struct s3c2410fb_mach_info *mach_info = fbvar->dev->platform_data;

    /*获得临时调色板寄存器基地址，S3C2410_TPAL宏定义在mach-s3c2410/include/mach/regs-lcd.h中。
    注意对于lpcsel这是一个针对三星TFT屏的一个专用寄存器，如果用的不是三星的TFT屏应该不用管它。*/
    tpal = fbvar->lcd_base + S3C2410_TPAL;
    lpcsel = fbvar->lcd_base + S3C2410_LPCSEL;

    /*在修改下面寄存器值之前先屏蔽中断，将中断状态保存到flags中*/
    local_irq_save(flags);

    /*这里就是在上一篇章中讲到的把IO端口C和D配置成LCD模式*/
    modify_gpio(S3C2410_GPCUP, mach_info->gpcup, mach_info->gpcup_mask);
    modify_gpio(S3C2410_GPCCON, mach_info->gpccon, mach_info->gpccon_mask);
    modify_gpio(S3C2410_GPDUP, mach_info->gpdup, mach_info->gpdup_mask);
    modify_gpio(S3C2410_GPDCON, mach_info->gpdcon, mach_info->gpdcon_mask);

    /*恢复被屏蔽的中断*/
    local_irq_restore(flags);

    writel(0x00, tpal);/*临时调色板寄存器使能禁止*/
    writel(mach_info->lpcsel, lpcsel);/*在上一篇中讲到过，它是三星TFT屏的一个寄存器，这里可以不管*/

    return 0;
}

/*该函数实现修改GPIO端口的值，注意第三个参数mask的作用是将要设置的寄存器值先清零*/
static inline void modify_gpio(void __iomem *reg, unsigned long set, unsigned longmask)
{
    unsigned long tmp;

    tmp = readl(reg) & ~mask;
    writel(tmp | set, reg);
}

/*检查fb_info中的可变参数*/
static int my2440fb_check_var(struct fb_info *fbinfo)
{
    unsigned i;

    /*从lcd_fb_probe探测函数设置的平台数据中再获得LCD相关信息的数据*/
    struct fb_var_screeninfo *var = &fbinfo->var;/*fb_info中的可变参数*/
    struct my2440fb_var    *fbvar = fbinfo->par;/*在lcd_fb_probe探测函数中设置的私有结构体数据*/
    struct s3c2410fb_mach_info *mach_info = fbvar->dev->platform_data;/*LCD的配置结构体数据，这个配置结构体的赋值在上一篇章的"3. 帧缓冲设备作为平台设备"中*/

    struct s3c2410fb_display *display = NULL;
    struct s3c2410fb_display *default_display = mach_info->displays +mach_info->default_display;
    int type = default_display->type;/*LCD的类型，看上一篇章的"3. 帧缓冲设备作为平台设备"中的type赋值是TFT类型*/

    /*验证X/Y解析度*/
    if (var->yres == default_display->yres &&
        var->xres == default_display->xres &&
        var->bits_per_pixel == default_display->bpp)
    {
        display = default_display;
    }
    else
    {
        for (i = 0; i < mach_info->num_displays; i++)
        {
            if (type == mach_info->displays[i].type &&
             var->yres == mach_info->displays[i].yres &&
             var->xres == mach_info->displays[i].xres &&
             var->bits_per_pixel == mach_info->displays[i].bpp)
            {
                display = mach_info->displays + i;
                break;
            }
        }
    }

    if (!display)
    {
        return -EINVAL;
    }

    /*配置LCD配置寄存器1中的5-6位(配置成TFT类型)和配置LCD配置寄存器5*/
    fbvar->regs.lcdcon1 = display->type;
    fbvar->regs.lcdcon5 = display->lcdcon5;

    /* 设置屏幕的虚拟解析像素和高度宽度 */
    var->xres_virtual = display->xres;
    var->yres_virtual = display->yres;
    var->height = display->height;
    var->width = display->width;

    /* 设置时钟像素，行、帧切换值，水平同步、垂直同步长度值 */
    var->pixclock = display->pixclock;
    var->left_margin = display->left_margin;
    var->right_margin = display->right_margin;
    var->upper_margin = display->upper_margin;
    var->lower_margin = display->lower_margin;
    var->vsync_len = display->vsync_len;
    var->hsync_len = display->hsync_len;

    /*设置透明度*/
    var->transp.offset = 0;
    var->transp.length = 0;

    /*根据色位模式(BPP)来设置可变参数中R、G、B的颜色位域。对于这些参数值的设置请参考CPU数据
    手册中"显示缓冲区与显示点对应关系图"，例如在上一篇章中我就画出了8BPP和16BPP时的对应关系图*/
    switch (var->bits_per_pixel)
    {
        case 1:
        case 2:
        case 4:
            var->red.offset  = 0;
            var->red.length  = var->bits_per_pixel;
            var->green       = var->red;
            var->blue        = var->red;
            break;
        case 8:/* 8 bpp 332 */
            if (display->type != S3C2410_LCDCON1_TFT)
            {
                var->red.length     = 3;
                var->red.offset     = 5;
                var->green.length   = 3;
                var->green.offset   = 2;
                var->blue.length    = 2;
                var->blue.offset    = 0;
            }else{
                var->red.offset     = 0;
                var->red.length     = 8;
                var->green          = var->red;
                var->blue           = var->red;
            }
            break;
        case 12:/* 12 bpp 444 */
            var->red.length         = 4;
            var->red.offset         = 8;
            var->green.length       = 4;
            var->green.offset       = 4;
            var->blue.length        = 4;
            var->blue.offset        = 0;
            break;
        case 16:/* 16 bpp */
            if (display->lcdcon5 & S3C2410_LCDCON5_FRM565)
            {
                /* 565 format */
                var->red.offset      = 11;
                var->green.offset    = 5;
                var->blue.offset     = 0;
                var->red.length      = 5;
                var->green.length    = 6;
                var->blue.length     = 5;
            } else {
                /* 5551 format */
                var->red.offset      = 11;
                var->green.offset    = 6;
                var->blue.offset     = 1;
                var->red.length      = 5;
                var->green.length    = 5;
                var->blue.length     = 5;
            }
            break;
        case 32:/* 24 bpp 888 and 8 dummy */
            var->red.length        = 8;
            var->red.offset        = 16;
            var->green.length      = 8;
            var->green.offset      = 8;
            var->blue.length       = 8;
            var->blue.offset       = 0;
            break;
    }

    return 0;
}

/*申请帧缓冲设备fb_info的显示缓冲区空间*/
static int __init my2440fb_map_video_memory(struct fb_info *fbinfo)
{
    dma_addr_t map_dma;/*用于保存DMA缓冲区总线地址*/
    struct my2440fb_var    *fbvar = fbinfo->par;/*获得在lcd_fb_probe探测函数中设置的私有结构体数据*/
    unsigned map_size = PAGE_ALIGN(fbinfo->fix.smem_len);/*获得FrameBuffer缓存的大小, PAGE_ALIGN定义在mm.h中*/

    /*将分配的一个写合并DMA缓存区设置为LCD屏幕的虚拟地址(对于DMA请参考DMA相关知识)
    dma_alloc_writecombine定义在arch/arm/mm/dma-mapping.c中*/
    fbinfo->screen_base = dma_alloc_writecombine(fbvar->dev, map_size, &map_dma,GFP_KERNEL);

    if (fbinfo->screen_base)
    {
        /*设置这片DMA缓存区的内容为空*/
        memset(fbinfo->screen_base, 0x00, map_size);

        /*将DMA缓冲区总线地址设成fb_info不可变参数中framebuffer缓存的开始位置*/
        fbinfo->fix.smem_start = map_dma;
    }

    return fbinfo->screen_base ? 0 : -ENOMEM;
}

/*释放帧缓冲设备fb_info的显示缓冲区空间*/
static inline void my2440fb_unmap_video_memory(struct fb_info *fbinfo)
{
    struct my2440fb_var    *fbvar = fbinfo->par;
    unsigned map_size = PAGE_ALIGN(fbinfo->fix.smem_len);

    /*跟申请DMA的地方想对应*/
    dma_free_writecombine(fbvar->dev, map_size, fbinfo->screen_base, fbinfo->fix.smem_start);
}

/*LCD FrameBuffer设备移除的实现，注意这里使用一个__devexit宏，和lcd_fb_probe接口函数相对应。
  在Linux内核中，使用了大量不同的宏来标记具有不同作用的函数和数据结构，这些宏在include/linux/init.h
  头文件中定义，编译器通过这些宏可以把代码优化放到合适的内存位置，以减少内存占用和提高内核效率。
  __devinit、__devexit就是这些宏之一，在probe()和remove()函数中应该使用__devinit和__devexit宏。
  又当remove()函数使用了__devexit宏时，则在驱动结构体中一定要使用__devexit_p宏来引用remove()，
  所以在第①步中就用__devexit_p来引用lcd_fb_remove接口函数。*/
static int __devexit lcd_fb_remove(struct platform_device *pdev)
{
    struct fb_info *fbinfo = platform_get_drvdata(pdev);
    struct my2440fb_var    *fbvar = fbinfo->par;

    /*从系统中注销帧缓冲设备*/
    unregister_framebuffer(fbinfo);

    /*停止LCD控制器的工作*/
    my2440fb_lcd_enable(fbvar, 0);

    /*延迟一段时间，因为停止LCD控制器需要一点时间 */
    msleep(1);

    /*释放帧缓冲设备fb_info的显示缓冲区空间*/
    my2440fb_unmap_video_memory(fbinfo);

    /*将LCD平台数据清空和释放fb_info空间资源*/
    platform_set_drvdata(pdev, NULL);
    framebuffer_release(fbinfo);

    /*释放中断资源*/
    free_irq(fbvar->lcd_irq_no, fbvar);

    /*释放时钟资源*/
    if (fbvar->lcd_clock)
    {
        clk_disable(fbvar->lcd_clock);
        clk_put(fbvar->lcd_clock);
        fbvar->lcd_clock = NULL;
    }

    /*释放LCD IO空间映射的虚拟内存空间*/
    iounmap(fbvar->lcd_base);

    /*释放申请的LCD IO端口所占用的IO空间*/
    release_resource(fbvar->lcd_mem);
    kfree(fbvar->lcd_mem);

    return 0;
}

/*停止LCD控制器的工作*/
static void my2440fb_lcd_enable(struct my2440fb_var *fbvar, int enable)
{
    unsigned long flags;

    /*在修改下面寄存器值之前先屏蔽中断，将中断状态保存到flags中*/
    local_irq_save(flags);

    if (enable)
    {
        fbvar->regs.lcdcon1 |= S3C2410_LCDCON1_ENVID;
    }
    else
    {
        fbvar->regs.lcdcon1 &= ~S3C2410_LCDCON1_ENVID;
    }

    writel(fbvar->regs.lcdcon1, fbvar->lcd_base + S3C2410_LCDCON1);

    /*恢复被屏蔽的中断*/
    local_irq_restore(flags);
}

/*对LCD FrameBuffer平台设备驱动电源管理的支持,CONFIG_PM这个宏定义在内核中*/
#ifdef CONFIG_PM
/*当配置内核时选上电源管理，则平台设备的驱动就支持挂起和恢复功能*/
static int lcd_fb_suspend(struct platform_device *pdev, pm_message_t state)
{
    /*挂起LCD设备，注意这里挂起LCD时并没有保存LCD控制器的各种状态，所以在恢复后LCD不会继续显示挂起前的内容
     若要继续显示挂起前的内容，则要在这里保存LCD控制器的各种状态，这里就不讲这个了，以后讲到电源管理再讲*/
    struct fb_info *fbinfo = platform_get_drvdata(pdev);
    struct my2440fb_var    *fbvar = fbinfo->par;

    /*停止LCD控制器的工作*/
    my2440fb_lcd_enable(fbvar, 0);

    msleep(1);

    /*停止时钟*/
    clk_disable(fbvar->lcd_clock);

    return 0;
}

static int lcd_fb_resume(struct platform_device *pdev)
{
    /*恢复挂起的LCD设备*/
    struct fb_info *fbinfo = platform_get_drvdata(pdev);
    struct my2440fb_var    *fbvar = fbinfo->par;

    /*开启时钟*/
    clk_enable(fbvar->lcd_clock);

    /*初始化LCD控制器之前要延迟一段时间*/
    msleep(1);

    /*恢复时重新初始化LCD各寄存器*/
    my2440fb_init_registers(fbinfo);

    /*重新激活fb_info中所有的参数配置，该函数定义在第③步中再讲*/
    my2440fb_activate_var(fbinfo);

    /*正与挂起时讲到的那样，因为没保存挂起时LCD控制器的各种状态，
    所以恢复后就让LCD显示空白，该函数定义也在第③步中再讲*/
    my2440fb_blank(FB_BLANK_UNBLANK, fbinfo);

    return 0;
}
#else
/*如果配置内核时没选上电源管理,则平台设备的驱动就不支持挂起和恢复功能,这两个函数也就无需实现了*/
#define lcd_fb_suspend    NULL
#define lcd_fb_resume    NULL
#endif

-

fbinfo->pseudo_palette = &fbvar->pseudo_pal;

③、帧缓冲设备驱动对底层硬件操作的函数接口实现(即：my2440fb_ops的实现)：

/*Framebuffer底层硬件操作各接口函数*/ static struct fb_ops my2440fb_ops = { .owner = THIS_MODULE, .fb_check_var = my2440fb_check_var,/*第②步中已实现*/ .fb_set_par = my2440fb_set_par,/*设置fb_info中的参数，主要是LCD的显示模式*/ .fb_blank = my2440fb_blank,/*显示空白(即：LCD开关控制)*/ .fb_setcolreg = my2440fb_setcolreg,/*设置颜色表*/ /*以下三个函数是可选的，主要是提供fb_console的支持，在内核中已经实现，这里直接调用即可*/ .fb_fillrect = cfb_fillrect,/*定义在drivers/video/cfbfillrect.c中*/ .fb_copyarea = cfb_copyarea,/*定义在drivers/video/cfbcopyarea.c中*/ .fb_imageblit = cfb_imageblit,/*定义在drivers/video/cfbimgblt.c中*/ }; /*设置fb_info中的参数，这里根据用户设置的可变参数var调整固定参数fix*/ static int my2440fb_set_par(struct fb_info *fbinfo) { /*获得fb_info中的可变参数*/ struct fb_var_screeninfo *var = &fbinfo->var; /*判断可变参数中的色位模式，根据色位模式来设置色彩模式*/ switch (var->bits_per_pixel) { case 32: case 16: case 12:/*12BPP时，设置为真彩色(分成红、绿、蓝三基色)*/ fbinfo->fix.visual = FB_VISUAL_TRUECOLOR; break; case 1:/*1BPP时，设置为黑白色(分黑、白两种色，FB_VISUAL_MONO01代表黑，FB_VISUAL_MONO10代表白)*/ fbinfo->fix.visual = FB_VISUAL_MONO01; break; default:/*默认设置为伪彩色，采用索引颜色显示*/ fbinfo->fix.visual = FB_VISUAL_PSEUDOCOLOR; break; } /*设置fb_info中固定参数中一行的字节数，公式：1行字节数=(1行像素个数*每像素位数BPP)/8 */ fbinfo->fix.line_length = (var->xres_virtual * var->bits_per_pixel) / 8; /*修改以上参数后，重新激活fb_info中的参数配置(即：使修改后的参数在硬件上生效)*/ my2440fb_activate_var(fbinfo); return 0; } /*重新激活fb_info中的参数配置*/ static void my2440fb_activate_var(struct fb_info *fbinfo) { /*获得结构体变量*/ struct my2440fb_var *fbvar = fbinfo->par; void __iomem *regs = fbvar->lcd_base; /*获得fb_info可变参数*/ struct fb_var_screeninfo *var = &fbinfo->var; /*计算LCD控制寄存器1中的CLKVAL值, 根据数据手册中该寄存器的描述，计算公式如下： * STN屏：VCLK = HCLK / (CLKVAL * 2), CLKVAL要求>= 2 * TFT屏：VCLK = HCLK / [(CLKVAL + 1) * 2], CLKVAL要求>= 0*/ int clkdiv = my2440fb_calc_pixclk(fbvar, var->pixclock) / 2; /*获得屏幕的类型*/ int type = fbvar->regs.lcdcon1 & S3C2410_LCDCON1_TFT; if (type == S3C2410_LCDCON1_TFT) { /*根据数据手册按照TFT屏的要求配置LCD控制寄存器1-5*/ my2440fb_config_tft_lcd_regs(fbinfo, &fbvar->regs); --clkdiv; if (clkdiv < 0) { clkdiv = 0; } } else { /*根据数据手册按照STN屏的要求配置LCD控制寄存器1-5*/ my2440fb_config_stn_lcd_regs(fbinfo, &fbvar->regs); if (clkdiv < 2) { clkdiv = 2; } } /*设置计算的LCD控制寄存器1中的CLKVAL值*/ fbvar->regs.lcdcon1 |= S3C2410_LCDCON1_CLKVAL(clkdiv); /*将各参数值写入LCD控制寄存器1-5中*/ writel(fbvar->regs.lcdcon1 & ~S3C2410_LCDCON1_ENVID, regs +S3C2410_LCDCON1); writel(fbvar->regs.lcdcon2, regs + S3C2410_LCDCON2); writel(fbvar->regs.lcdcon3, regs + S3C2410_LCDCON3); writel(fbvar->regs.lcdcon4, regs + S3C2410_LCDCON4); writel(fbvar->regs.lcdcon5, regs + S3C2410_LCDCON5); /*配置帧缓冲起始地址寄存器1-3*/ my2440fb_set_lcdaddr(fbinfo); fbvar->regs.lcdcon1 |= S3C2410_LCDCON1_ENVID, writel(fbvar->regs.lcdcon1, regs + S3C2410_LCDCON1); } /*计算LCD控制寄存器1中的CLKVAL值*/ static unsigned int my2440fb_calc_pixclk(struct my2440fb_var *fbvar, unsignedlong pixclk) { /*获得LCD的时钟*/ unsigned long clk = clk_get_rate(fbvar->lcd_clock); /* 像素时钟单位是皮秒，而时钟的单位是赫兹，所以计算公式为： * Hz -> picoseconds is / 10^-12 */ unsigned long long div = (unsigned long long)clk * pixclk; div >>= 12; /* div / 2^12 */ do_div(div, 625 * 625UL * 625); /* div / 5^12, do_div宏定义在asm/div64.h中*/ return div; } /*根据数据手册按照TFT屏的要求配置LCD控制寄存器1-5*/ static void my2440fb_config_tft_lcd_regs(const struct fb_info *fbinfo, structs3c2410fb_hw *regs) { const struct my2440fb_var *fbvar = fbinfo->par; const struct fb_var_screeninfo *var = &fbinfo->var; /*根据色位模式设置LCD控制寄存器1和5，参考数据手册*/ switch (var->bits_per_pixel) { case 1:/*1BPP*/ regs->lcdcon1 |= S3C2410_LCDCON1_TFT1BPP; break; case 2:/*2BPP*/ regs->lcdcon1 |= S3C2410_LCDCON1_TFT2BPP; break; case 4:/*4BPP*/ regs->lcdcon1 |= S3C2410_LCDCON1_TFT4BPP; break; case 8:/*8BPP*/ regs->lcdcon1 |= S3C2410_LCDCON1_TFT8BPP; regs->lcdcon5 |= S3C2410_LCDCON5_BSWP |S3C2410_LCDCON5_FRM565; regs->lcdcon5 &= ~S3C2410_LCDCON5_HWSWP; break; case 16:/*16BPP*/ regs->lcdcon1 |= S3C2410_LCDCON1_TFT16BPP; regs->lcdcon5 &= ~S3C2410_LCDCON5_BSWP; regs->lcdcon5 |= S3C2410_LCDCON5_HWSWP; break; case 32:/*32BPP*/ regs->lcdcon1 |= S3C2410_LCDCON1_TFT24BPP; regs->lcdcon5 &= ~(S3C2410_LCDCON5_BSWP |S3C2410_LCDCON5_HWSWP | S3C2410_LCDCON5_BPP24BL); break; default:/*无效的BPP*/ dev_err(fbvar->dev, "invalid bpp %d/n", var->bits_per_pixel); } /*设置LCD配置寄存器2、3、4*/ regs->lcdcon2 = S3C2410_LCDCON2_LINEVAL(var->yres - 1) | S3C2410_LCDCON2_VBPD(var->upper_margin - 1) | S3C2410_LCDCON2_VFPD(var->lower_margin - 1) | S3C2410_LCDCON2_VSPW(var->vsync_len - 1); regs->lcdcon3 = S3C2410_LCDCON3_HBPD(var->right_margin - 1) | S3C2410_LCDCON3_HFPD(var->left_margin - 1) | S3C2410_LCDCON3_HOZVAL(var->xres - 1); regs->lcdcon4 = S3C2410_LCDCON4_HSPW(var->hsync_len - 1); } /*根据数据手册按照STN屏的要求配置LCD控制寄存器1-5*/ static void my2440fb_config_stn_lcd_regs(const struct fb_info *fbinfo, structs3c2410fb_hw *regs) { const struct my2440fb_var *fbvar = fbinfo->par; const struct fb_var_screeninfo *var = &fbinfo->var; int type = regs->lcdcon1 & ~S3C2410_LCDCON1_TFT; int hs = var->xres >> 2; unsigned wdly = (var->left_margin >> 4) - 1; unsigned wlh = (var->hsync_len >> 4) - 1; if (type != S3C2410_LCDCON1_STN4) { hs >>= 1; } /*根据色位模式设置LCD控制寄存器1，参考数据手册*/ switch (var->bits_per_pixel) { case 1:/*1BPP*/ regs->lcdcon1 |= S3C2410_LCDCON1_STN1BPP; break; case 2:/*2BPP*/ regs->lcdcon1 |= S3C2410_LCDCON1_STN2GREY; break; case 4:/*4BPP*/ regs->lcdcon1 |= S3C2410_LCDCON1_STN4GREY; break; case 8:/*8BPP*/ regs->lcdcon1 |= S3C2410_LCDCON1_STN8BPP; hs *= 3; break; case 12:/*12BPP*/ regs->lcdcon1 |= S3C2410_LCDCON1_STN12BPP; hs *= 3; break; default:/*无效的BPP*/ dev_err(fbvar->dev, "invalid bpp %d/n", var->bits_per_pixel); } /*设置LCD配置寄存器2、3、4, 参考数据手册*/ if (wdly > 3) wdly = 3; if (wlh > 3) wlh = 3; regs->lcdcon2 = S3C2410_LCDCON2_LINEVAL(var->yres - 1); regs->lcdcon3 = S3C2410_LCDCON3_WDLY(wdly) | S3C2410_LCDCON3_LINEBLANK(var->right_margin / 8) | S3C2410_LCDCON3_HOZVAL(hs - 1); regs->lcdcon4 = S3C2410_LCDCON4_WLH(wlh); } /*配置帧缓冲起始地址寄存器1-3，参考数据手册*/ static void my2440fb_set_lcdaddr(struct fb_info *fbinfo) { unsigned long saddr1, saddr2, saddr3; struct my2440fb_var *fbvar = fbinfo->par; void __iomem *regs = fbvar->lcd_base; saddr1 = fbinfo->fix.smem_start >> 1; saddr2 = fbinfo->fix.smem_start; saddr2 += fbinfo->fix.line_length * fbinfo->var.yres; saddr2 >>= 1; saddr3 = S3C2410_OFFSIZE(0) | S3C2410_PAGEWIDTH((fbinfo->fix.line_length/ 2) & 0x3ff); writel(saddr1, regs + S3C2410_LCDSADDR1); writel(saddr2, regs + S3C2410_LCDSADDR2); writel(saddr3, regs + S3C2410_LCDSADDR3); } /*显示空白，blank mode有5种模式，定义在fb.h中，是一个枚举*/ static int my2440fb_blank(int blank_mode, struct fb_info *fbinfo) { struct my2440fb_var *fbvar = fbinfo->par; void __iomem *regs = fbvar->lcd_base; /*根据显示空白的模式来设置LCD是开启还是停止*/ if (blank_mode == FB_BLANK_POWERDOWN) { my2440fb_lcd_enable(fbvar, 0);/*在第②步中定义*/ } else { my2440fb_lcd_enable(fbvar, 1);/*在第②步中定义*/ } /*根据显示空白的模式来控制临时调色板寄存器*/ if (blank_mode == FB_BLANK_UNBLANK) { /*临时调色板寄存器无效*/ writel(0x0, regs + S3C2410_TPAL); } else { /*临时调色板寄存器有效*/ writel(S3C2410_TPAL_EN, regs + S3C2410_TPAL); } return 0; } /*设置颜色表*/ static int my2440fb_setcolreg(unsigned regno,unsigned red,unsignedgreen,unsigned blue,unsigned transp,struct fb_info *fbinfo) { unsigned int val; struct my2440fb_var *fbvar = fbinfo->par; void __iomem *regs = fbvar->lcd_base; switch (fbinfo->fix.visual) { case FB_VISUAL_TRUECOLOR: /*真彩色*/ if (regno < 16) { u32 *pal = fbinfo->pseudo_palette; val = chan_to_field(red, &fbinfo->var.red); val |= chan_to_field(green, &fbinfo->var.green); val |= chan_to_field(blue, &fbinfo->var.blue); pal[regno] = val; } break; case FB_VISUAL_PSEUDOCOLOR: /*伪彩色*/ if (regno < 256) { val = (red >> 0) & 0xf800; val |= (green >> 5) & 0x07e0; val |= (blue >> 11) & 0x001f; writel(val, regs + S3C2410_TFTPAL(regno)); /*修改调色板*/ schedule_palette_update(fbvar, regno, val); } break; default: return 1; } return 0; } static inline unsigned int chan_to_field(unsigned int chan, struct fb_bitfield *bf) { chan &= 0xffff; chan >>= 16 - bf->length; return chan << bf->offset; } /*修改调色板*/ static void schedule_palette_update(struct my2440fb_var *fbvar, unsigned intregno, unsigned int val) { unsigned long flags; unsigned long irqen; /*LCD中断挂起寄存器基地址*/ void __iomem *lcd_irq_base = fbvar->lcd_base + S3C2410_LCDINTBASE; /*在修改中断寄存器值之前先屏蔽中断，将中断状态保存到flags中*/ local_irq_save(flags); fbvar->palette_buffer[regno] = val; /*判断调色板是否准备就像*/ if (!fbvar->palette_ready) { fbvar->palette_ready = 1; /*使能中断屏蔽寄存器*/ irqen = readl(lcd_irq_base + S3C24XX_LCDINTMSK); irqen &= ~S3C2410_LCDINT_FRSYNC; writel(irqen, lcd_irq_base + S3C24XX_LCDINTMSK); } /*恢复被屏蔽的中断*/ local_irq_restore(flags); }

五、从整体上再描述一下FrameBuffer设备驱动实例代码的结构：

1、在第①部分代码中主要做的事情有：

a.将LCD设备注册到系统平台设备中；

b.定义LCD平台设备结构体lcd_fb_driver。

2、在第②部分代码中主要做的事情有：

a.获取和设置LCD平台设备的各种资源；

b.分配fb_info结构体空间；

c.初始化fb_info结构体中的各参数；

d.初始化LCD控制器；

e.检查fb_info中可变参数；

f.申请帧缓冲设备的显示缓冲区空间；

g.注册fb_info。

3、在第③部分代码中主要做的事情有：

a.实现对fb_info相关参数进行检查的硬件接口函数；

b.实现对LCD显示模式进行设定的硬件接口函数；

c.实现对LCD显示开关(空白)的硬件接口函数等。

memcpy

//这里就是将内核中定义的s3c2410fb_mach_info结构体数据保存到LCD平台数据中，所以在写驱动的时候就可以直接在平台数据中获取s3c2410fb_mach_info结构体的数据(即LCD各种参数信息)进行操作 s3c_device_lcd.dev.platform_data = npd; } else { printk(KERN_ERR "no memory for LCD platform data/n"); } }

//S3C2440初始化函数 static void __init smdk2440_machine_init(void) {

//调用该函数将上面定义的LCD硬件信息保存到平台数据中 s3c24xx_fb_set_platdata(&smdk2440_fb_info); s3c_i2c0_set_platdata(NULL); platform_add_devices(smdk2440_devices, ARRAY_SIZE(smdk2440_devices)); smdk_machine_init(); }

/* LCD Controller */

//LCD控制器的资源信息 static struct resource s3c_lcd_resource[] = { [0] = { .start = S3C24XX_PA_LCD, //控制器IO端口开始地址 .end = S3C24XX_PA_LCD + S3C24XX_SZ_LCD - 1,//控制器IO端口结束地址 .flags = IORESOURCE_MEM,//标识为LCD控制器IO端口，在驱动中引用这个就表示引用IO端口 }, [1] = { .start = IRQ_LCD,//LCD中断 .end = IRQ_LCD, .flags = IORESOURCE_IRQ,//标识为LCD中断 } }; static u64 s3c_device_lcd_dmamask = 0xffffffffUL; struct platform_device s3c_device_lcd = { .name = "s3c2410-lcd",//作为平台设备的LCD设备名 .id = -1, .num_resources = ARRAY_SIZE(s3c_lcd_resource),//资源数量 .resource = s3c_lcd_resource,//引用上面定义的资源 .dev = { .dma_mask = &s3c_device_lcd_dmamask, .coherent_dma_mask = 0xffffffffUL } }; EXPORT_SYMBOL(s3c_device_lcd);//导出定义的LCD平台设备，好在mach-smdk2440.c的smdk2440_devices[]中添加到平台设备列表中

struct fb_info { int node; int flags; struct fb_var_screeninfo var;/*LCD可变参数结构体*/ struct fb_fix_screeninfo fix;/*LCD固定参数结构体*/ struct fb_monspecs monspecs; /*LCD显示器标准*/ struct work_struct queue; /*帧缓冲事件队列*/ struct fb_pixmap pixmap; /*图像硬件mapper*/ struct fb_pixmap sprite; /*光标硬件mapper*/ struct fb_cmap cmap; /*当前的颜色表*/ struct fb_videomode *mode; /*当前的显示模式*/ #ifdef CONFIG_FB_BACKLIGHT struct backlight_device *bl_dev;/*对应的背光设备*/ struct mutex bl_curve_mutex; u8 bl_curve[FB_BACKLIGHT_LEVELS];/*背光调整*/ #endif #ifdef CONFIG_FB_DEFERRED_IO struct delayed_work deferred_work; struct fb_deferred_io *fbdefio; #endif struct fb_ops *fbops; /*对底层硬件操作的函数指针*/ struct device *device; struct device *dev; /*fb设备*/ int class_flag; #ifdef CONFIG_FB_TILEBLITTING struct fb_tile_ops *tileops; /*图块Blitting*/ #endif char __iomem *screen_base; /*虚拟基地址*/ unsigned long screen_size; /*LCD IO映射的虚拟内存大小*/ void *pseudo_palette; /*伪16色颜色表*/ #define FBINFO_STATE_RUNNING 0 #define FBINFO_STATE_SUSPENDED 1 u32 state; /*LCD的挂起或恢复状态*/ void *fbcon_par; void *par; };

其中，比较重要的成员有struct fb_var_screeninfo var、struct fb_fix_screeninfo fix和structfb_ops *fbops，他们也都是结构体。下面我们一个一个的来看。

fb_var_screeninfo结构体主要记录用户可以修改的控制器的参数，比如屏幕的分辨率和每个像素的比特数等，该结构体定义如下：

而fb_fix_screeninfo结构体又主要记录用户不可以修改的控制器的参数，比如屏幕缓冲区的物理地址和长度等，该结构体的定义如下：

struct fb_fix_screeninfo { char id[16]; /*字符串形式的标示符 */ unsigned long smem_start; /*fb缓存的开始位置 */ __u32 smem_len; /*fb缓存的长度 */ __u32 type; /*看FB_TYPE_* */ __u32 type_aux; /*分界*/ __u32 visual; /*看FB_VISUAL_* */ __u16 xpanstep; /*如果没有硬件panning就赋值为0 */ __u16 ypanstep; /*如果没有硬件panning就赋值为0 */ __u16 ywrapstep; /*如果没有硬件ywrap就赋值为0 */ __u32 line_length; /*一行的字节数 */ unsigned long mmio_start; /*内存映射IO的开始位置*/ __u32 mmio_len; /*内存映射IO的长度*/ __u32 accel; __u16 reserved[3]; /*保留*/ };

struct fb_var_screeninfo { __u32 xres; /*可见屏幕一行有多少个像素点*/ __u32 yres; /*可见屏幕一列有多少个像素点*/ __u32 xres_virtual; /*虚拟屏幕一行有多少个像素点*/ __u32 yres_virtual; /*虚拟屏幕一列有多少个像素点*/ __u32 xoffset; /*虚拟到可见屏幕之间的行偏移*/ __u32 yoffset; /*虚拟到可见屏幕之间的列偏移*/ __u32 bits_per_pixel; /*每个像素的位数即BPP*/ __u32 grayscale; /*非0时，指的是灰度*/ struct fb_bitfield red; /*fb缓存的R位域*/ struct fb_bitfield green; /*fb缓存的G位域*/ struct fb_bitfield blue; /*fb缓存的B位域*/ struct fb_bitfield transp; /*透明度*/ __u32 nonstd; /* != 0 非标准像素格式*/ __u32 activate; __u32 height; /*高度*/ __u32 width; /*宽度*/ __u32 accel_flags; /*定时：除了pixclock本身外，其他的都以像素时钟为单位*/ __u32 pixclock; /*像素时钟(皮秒)*/ __u32 left_margin; /*行切换，从同步到绘图之间的延迟*/ __u32 right_margin; /*行切换，从绘图到同步之间的延迟*/ __u32 upper_margin; /*帧切换，从同步到绘图之间的延迟*/ __u32 lower_margin; /*帧切换，从绘图到同步之间的延迟*/ __u32 hsync_len; /*水平同步的长度*/ __u32 vsync_len; /*垂直同步的长度*/ __u32 sync; __u32 vmode; __u32 rotate; __u32 reserved[5]; /*保留*/ };

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原文地址：https://www.cnblogs.com/big-devil/p/8590093.html