内核版本:3.9.5
SPI控制器层(平台相关)
上一节讲了SPI核心层的注册和匹配函数,它是平台无关的.正是在核心层抽象了SPI控制器层的相同部分然后提供了统一的API给SPI设备层来使用.我们这一节就能看到,一个SPI控制器以platform_device的形式注册进内核,并且调用spi_register_board_info函数注册了spi_board_info结构.我们前面说过,struct spi_board_info结构是对spi_device的描述,其中的内从最终是要用来初始化struct spi_device实例的.
哎!闲话少说了,越说越糊涂.我们以davinci的dm365平台为例,来看看SPI控制器的相关内容.在arch/arm/mach-davinci/board-dm365-evm.c中有:
1 static struct spi_board_info dm365_evm_spi_info[] __initconst = { 2 { 3 .modalias = "at25", 4 .platform_data = &at25640, 5 .max_speed_hz = 10 * 1000 * 1000, 6 .bus_num = 0, 7 .chip_select = 0, 8 .mode = SPI_MODE_0, 9 }, 10 }; 11 12 static __init void dm365_evm_init(void) 13 { 14 …… 15 dm365_init_spi0(BIT(0), dm365_evm_spi_info, 16 ARRAY_SIZE(dm365_evm_spi_info)); 17 }
dm365_evm_init这个函数是dm365平台初始化函数,我略去了和SPI无关的部分.可以看到其中调用了dm365_init_spi0函数,并且将一个struct spi_board_info这个结构类型的数组作为参数传了进去.那么来看看dm365_init_spi0函数,在arch/arm/mach-davinci/dm365.c中:
1 static u64 dm365_spi0_dma_mask = DMA_BIT_MASK(32); 2 3 static struct davinci_spi_platform_data dm365_spi0_pdata = { 4 .version = SPI_VERSION_1, 5 .num_chipselect = 2, 6 .dma_event_q = EVENTQ_3, 7 }; 8 9 static struct resource dm365_spi0_resources[] = { 10 { 11 .start = 0x01c66000, 12 .end = 0x01c667ff, 13 .flags = IORESOURCE_MEM, 14 }, 15 { 16 .start = IRQ_DM365_SPIINT0_0, 17 .flags = IORESOURCE_IRQ, 18 }, 19 { 20 .start = 17, 21 .flags = IORESOURCE_DMA, 22 }, 23 { 24 .start = 16, 25 .flags = IORESOURCE_DMA, 26 }, 27 }; 28 29 static struct platform_device dm365_spi0_device = { 30 .name = "spi_davinci",/*这个是和platform_driver匹配的依据,具体到davinci的板子就是davinci_spi_driver*/ 31 .id = 0,/*对于SPI,这个值最后会在初始化spi_master的时候用来初始化master->bus_num*/ 32 .dev = { 33 .dma_mask = &dm365_spi0_dma_mask, 34 .coherent_dma_mask = DMA_BIT_MASK(32), 35 .platform_data = &dm365_spi0_pdata, 36 }, 37 .num_resources = ARRAY_SIZE(dm365_spi0_resources), 38 .resource = dm365_spi0_resources, 39 }; 40 41 void __init dm365_init_spi0(unsigned chipselect_mask, 42 const struct spi_board_info *info, unsigned len) 43 { 44 davinci_cfg_reg(DM365_SPI0_SCLK); 45 davinci_cfg_reg(DM365_SPI0_SDI); 46 davinci_cfg_reg(DM365_SPI0_SDO); 47 48 /* not all slaves will be wired up */ 49 if (chipselect_mask & BIT(0)) 50 davinci_cfg_reg(DM365_SPI0_SDENA0); 51 if (chipselect_mask & BIT(1)) 52 davinci_cfg_reg(DM365_SPI0_SDENA1); 53 54 spi_register_board_info(info, len); 55 56 platform_device_register(&dm365_spi0_device); 57 }
第54行注册了struct spi_board_info实例,就是我们传进来的dm365_evm_spi_info.在设备移植时填充结构体spi_board_info是移植的重要工作.我们来看看这个函数的实现,在drivers/spi/spi.c中:
1 int spi_register_board_info(struct spi_board_info const *info, unsigned n) 2 { 3 struct boardinfo *bi; 4 int i; 5 6 bi = kzalloc(n * sizeof(*bi), GFP_KERNEL);/*为结构体boardinfo分配内存空间*/ 7 if (!bi) 8 return -ENOMEM; 9 10 for (i = 0; i < n; i++, bi++, info++) { 11 struct spi_master *master; 12 13 memcpy(&bi->board_info, info, sizeof(*info)); 14 mutex_lock(&board_lock); 15 list_add_tail(&bi->list, &board_list);/*添加到板级描述符链表*/ 16 list_for_each_entry(master, &spi_master_list, list)/*将SPI主机控制类链表所有的节点匹配板级信息的设备初始化*/ 17 spi_match_master_to_boardinfo(master, &bi->board_info); 18 mutex_unlock(&board_lock); 19 } 20 21 return 0; 22 }
这里又看到了一个结构struct boardinfo,其实它简单的就像没穿裤子的女人,我们来看,在同文件中:
1 struct boardinfo { 2 struct list_head list; 3 struct spi_board_info board_info; 4 }; 5 6 static LIST_HEAD(board_list); 7 static LIST_HEAD(spi_master_list); 8 9 /* 10 * Used to protect add/del opertion for board_info list and 11 * spi_master list, and their matching process 12 */ 13 /*boardinfo链表操作锁*/ 14 static DEFINE_MUTEX(board_lock);
这个结构是一个板级相关信息链表,就是说它是一些描述spi_device的信息的集合.结构体boardinfo管理多个结构体spi_board_info,结构体spi_board_info中挂在SPI总线上的设备的平台信息.一个结构体spi_board_info对应着一个SPI设备spi_device.
同时我们也看到了,函数中出现的board_list和spi_master_list都是全局的链表,她们分别记录了系统中所有的boardinfo和所有的spi_master.至于spi_match_master_to_boardinfo函数是什么意思,我们后面还会遇到,到时候再讲.
dm365_init_spi0函数中第56行注册平台设备.我们看到这个platform_device的的name是"spi_davinci",那么就必然还存在一个名为"spi_davinci"的platform_driver.那好办了,搜一下发现在drivers/spi/spi_davinci.c中:
1 static struct platform_driver davinci_spi_driver = { 2 .driver = { 3 .name = "spi_davinci", 4 .owner = THIS_MODULE, 5 .of_match_table = davinci_spi_of_match, 6 }, 7 .probe = davinci_spi_probe, 8 .remove = davinci_spi_remove, 9 }; 10 module_platform_driver(davinci_spi_driver);
Linux设备模型常识告诉我们,当系统中注册了一个名为"spi_davinci"的platform_device时,同时又住了一个名为"spi_davinci"的platform_driver.那么就会执行这里的probe回调.这里我们来看davinci_spi_probe函数.
1 static int davinci_spi_probe(struct platform_device *pdev) 2 { 3 struct spi_master *master; 4 struct davinci_spi *dspi;/*davinci_spi这个结构用来描述具体的davinci平台上的spi控制器,等于说是对spi_master的一个封装*/ 5 struct davinci_spi_platform_data *pdata; 6 struct resource *r, *mem; 7 resource_size_t dma_rx_chan = SPI_NO_RESOURCE; 8 resource_size_t dma_tx_chan = SPI_NO_RESOURCE; 9 int i = 0, ret = 0; 10 u32 spipc0; 11 12 /*分配master结构体,其中包括davinci_spi结构的内存空间,使用master.dev.driver_data指向它*/ 13 master = spi_alloc_master(&pdev->dev, sizeof(struct davinci_spi)); 14 if (master == NULL) { 15 ret = -ENOMEM; 16 goto err; 17 } 18 19 dev_set_drvdata(&pdev->dev, master);/*pdev->dev.device_private->driver_data = master*/ 20 21 dspi = spi_master_get_devdata(master);/*就是获取上文master.dev.driver_data指向的对象地址,其实就是davinci_spi结构对象的空间地址,将 22 其赋给dspi*/ 23 if (dspi == NULL) {/*dspi不能为空哦*/ 24 ret = -ENOENT; 25 goto free_master; 26 } 27 28 /*下面这几行就是填充dspi的pdata字段*/ 29 if (pdev->dev.platform_data) { 30 pdata = pdev->dev.platform_data;/*具体到对于dm365来说就是dm365_spi0_pdata*/ 31 dspi->pdata = *pdata; 32 } else { 33 /* update dspi pdata with that from the DT */ 34 ret = spi_davinci_get_pdata(pdev, dspi); 35 if (ret < 0) 36 goto free_master; 37 } 38 39 /* pdata in dspi is now updated and point pdata to that */ 40 pdata = &dspi->pdata;/*pdata指针再指向dspi->pdata*/ 41 42 r = platform_get_resource(pdev, IORESOURCE_MEM, 0);/*获取IO资源*/ 43 if (r == NULL) { 44 ret = -ENOENT; 45 goto free_master; 46 } 47 48 dspi->pbase = r->start; 49 50 mem = request_mem_region(r->start, resource_size(r), pdev->name);/*申请IO内存*/ 51 if (mem == NULL) { 52 ret = -EBUSY; 53 goto free_master; 54 } 55 56 dspi->base = ioremap(r->start, resource_size(r));/*建立内存映射*/ 57 if (dspi->base == NULL) { 58 ret = -ENOMEM; 59 goto release_region; 60 } 61 62 dspi->irq = platform_get_irq(pdev, 0);/*获取irq号*/ 63 if (dspi->irq <= 0) { 64 ret = -EINVAL; 65 goto unmap_io; 66 } 67 68 ret = request_threaded_irq(dspi->irq, davinci_spi_irq, dummy_thread_fn, 69 0, dev_name(&pdev->dev), dspi);/*申请spi中断,中断处理函数为davinci_spi_irq*/ 70 if (ret) 71 goto unmap_io; 72 73 /*设置bitbang的所属master*/ 74 dspi->bitbang.master = spi_master_get(master); 75 if (dspi->bitbang.master == NULL) { 76 ret = -ENODEV; 77 goto irq_free; 78 } 79 80 dspi->clk = clk_get(&pdev->dev, NULL);/*获取spi时钟*/ 81 if (IS_ERR(dspi->clk)) { 82 ret = -ENODEV; 83 goto put_master; 84 } 85 clk_prepare_enable(dspi->clk); 86 87 master->dev.of_node = pdev->dev.of_node; 88 master->bus_num = pdev->id;/*bus_num*/ 89 master->num_chipselect = pdata->num_chipselect;/*保存SPI主机控制器支持的片选数量.具体到dm365可以看到dm365_spi0_pdata中将其定义为2*/ 90 master->setup = davinci_spi_setup; 91 92 /*设置bitbang控制传输的相关函数*/ 93 dspi->bitbang.chipselect = davinci_spi_chipselect; 94 dspi->bitbang.setup_transfer = davinci_spi_setup_transfer; 95 96 dspi->version = pdata->version;/*具体到dm365可以看到dm365_spi0_pdata中将其定义为0*/ 97 98 dspi->bitbang.flags = SPI_NO_CS | SPI_LSB_FIRST | SPI_LOOP; 99 if (dspi->version == SPI_VERSION_2) 100 dspi->bitbang.flags |= SPI_READY; 101 102 r = platform_get_resource(pdev, IORESOURCE_DMA, 0);/*获取DMA资源,这作为输入缓冲*/ 103 if (r) 104 dma_rx_chan = r->start; 105 r = platform_get_resource(pdev, IORESOURCE_DMA, 1);/*由参数就能知道davinci的DMA资源定义了两个,这里就获取第二个.这作为输出缓冲*/ 106 if (r) 107 dma_tx_chan = r->start; 108 109 dspi->bitbang.txrx_bufs = davinci_spi_bufs;/*传输数据最终要调用的函数*/ 110 if (dma_rx_chan != SPI_NO_RESOURCE && 111 dma_tx_chan != SPI_NO_RESOURCE) { 112 dspi->dma_rx_chnum = dma_rx_chan; 113 dspi->dma_tx_chnum = dma_tx_chan; 114 115 ret = davinci_spi_request_dma(dspi); 116 if (ret) 117 goto free_clk; 118 119 dev_info(&pdev->dev, "DMA: supported "); 120 dev_info(&pdev->dev, "DMA: RX channel: %d, TX channel: %d, " 121 "event queue: %d ", dma_rx_chan, dma_tx_chan, 122 pdata->dma_event_q); 123 } 124 125 dspi->get_rx = davinci_spi_rx_buf_u8; 126 dspi->get_tx = davinci_spi_tx_buf_u8; 127 128 init_completion(&dspi->done);/*初始化completion,用于实现同步I/O*/ 129 130 /* Reset In/OUT SPI module */ 131 iowrite32(0, dspi->base + SPIGCR0); 132 udelay(100); 133 iowrite32(1, dspi->base + SPIGCR0); 134 135 /* Set up SPIPC0. CS and ENA init is done in davinci_spi_setup */ 136 spipc0 = SPIPC0_DIFUN_MASK | SPIPC0_DOFUN_MASK | SPIPC0_CLKFUN_MASK; 137 iowrite32(spipc0, dspi->base + SPIPC0); 138 139 /* initialize chip selects */ 140 if (pdata->chip_sel) {/*davinci的pdata中chip_sel字段并没有设置,这里为空,因此不会进来*/ 141 for (i = 0; i < pdata->num_chipselect; i++) { 142 if (pdata->chip_sel[i] != SPI_INTERN_CS) 143 gpio_direction_output(pdata->chip_sel[i], 1); 144 } 145 } 146 147 if (pdata->intr_line)/*dm365这个字段为空*/ 148 iowrite32(SPI_INTLVL_1, dspi->base + SPILVL); 149 else 150 iowrite32(SPI_INTLVL_0, dspi->base + SPILVL); 151 152 iowrite32(CS_DEFAULT, dspi->base + SPIDEF); 153 154 /* master mode default */ 155 set_io_bits(dspi->base + SPIGCR1, SPIGCR1_CLKMOD_MASK); 156 set_io_bits(dspi->base + SPIGCR1, SPIGCR1_MASTER_MASK);/*默认设置SPI主控制器工作在master方式*/ 157 set_io_bits(dspi->base + SPIGCR1, SPIGCR1_POWERDOWN_MASK); 158 159 ret = spi_bitbang_start(&dspi->bitbang);/*注册我们的主机SPI控制器*/ 160 if (ret) 161 goto free_dma; 162 163 dev_info(&pdev->dev, "Controller at 0x%p ", dspi->base); 164 165 return ret; 166 167 free_dma: 168 dma_release_channel(dspi->dma_rx); 169 dma_release_channel(dspi->dma_tx); 170 free_clk: 171 clk_disable_unprepare(dspi->clk); 172 clk_put(dspi->clk); 173 put_master: 174 spi_master_put(master);/*减少引用计数*/ 175 irq_free: 176 free_irq(dspi->irq, dspi); 177 unmap_io: 178 iounmap(dspi->base); 179 release_region: 180 release_mem_region(dspi->pbase, resource_size(r)); 181 free_master: 182 kfree(master); 183 err: 184 return ret; 185 }
该函数首先为spi_master结构体以及davinci_spi结构体分配了空间,同时,spi_master.dev.driver_data指向了davinci_spi.接着执行了该条语句:
pdata = pdev->dev.platform_data;/*具体到对于dm365来说就是dm365_spi0_pdata*/
dspi->pdata = *pdata;
NOTE:在这里获取platform_device.dev.platform_data,也就是平台设备的相关数据,这是平台设备移植最需要关注的地方.
随后,为master定义了setup方法,为bitbang定义了3个方法.之后获取了一系列的资源,同时注册了中断服务程序.接着再初始化了completion,这个东东将用于实现同步I/O,他的伟大之处后面会体现出来的.最后调用spi_bitbang_start注册主机控制器.我们来看这个函数,在drivers/spi/spi_bitbang.c中:
1 int spi_bitbang_start(struct spi_bitbang *bitbang) 2 { 3 struct spi_master *master = bitbang->master; 4 int status; 5 6 if (!master || !bitbang->chipselect) 7 return -EINVAL; 8 9 INIT_WORK(&bitbang->work, bitbang_work);/*初始化一个struct work,处理函数为bitbang_work*/ 10 spin_lock_init(&bitbang->lock);/*初始化自旋锁*/ 11 INIT_LIST_HEAD(&bitbang->queue);/*初始化链表头,链表为双向循环链表*/ 12 13 if (!master->mode_bits) 14 master->mode_bits = SPI_CPOL | SPI_CPHA | bitbang->flags; 15 16 /*检测bitbang中的函数是否都定义了,如果没定义,则默认使用spi_bitbang_xxx*/ 17 if (!master->transfer)/*master的transfer方法没有定义过*/ 18 master->transfer = spi_bitbang_transfer;/*使用默认的spi_bitbang_transfe方法*/ 19 if (!bitbang->txrx_bufs) {/*如果bitbang没有txrx_bufs方法,其实对于davinci在davinci_spi_probe函数中定义过该方法*/ 20 bitbang->use_dma = 0; 21 bitbang->txrx_bufs = spi_bitbang_bufs; 22 if (!master->setup) { 23 if (!bitbang->setup_transfer) 24 bitbang->setup_transfer = 25 spi_bitbang_setup_transfer; 26 master->setup = spi_bitbang_setup; 27 master->cleanup = spi_bitbang_cleanup; 28 } 29 } else if (!master->setup)/*对于davinci在davinci_spi_probe函数中定义过该方法*/ 30 return -EINVAL; 31 if (master->transfer == spi_bitbang_transfer && 32 !bitbang->setup_transfer) 33 return -EINVAL; 34 35 /* this task is the only thing to touch the SPI bits */ 36 bitbang->busy = 0; 37 bitbang->workqueue = create_singlethread_workqueue( 38 dev_name(master->dev.parent));/*创建bitbang的工作队列*/ 39 if (bitbang->workqueue == NULL) { 40 status = -EBUSY; 41 goto err1; 42 } 43 44 /* driver may get busy before register() returns, especially 45 * if someone registered boardinfo for devices 46 */ 47 status = spi_register_master(master);/*注册spi控制器*/ 48 if (status < 0) 49 goto err2; 50 51 return status; 52 53 err2: 54 destroy_workqueue(bitbang->workqueue); 55 err1: 56 return status; 57 } 58 EXPORT_SYMBOL_GPL(spi_bitbang_start);
定义了控制器的transfer方法为spi_bitbang_transfer.创建了一个工作队列和一个工作bitbang_work,同时创建了一个链表.这些东东后面都会看到.最后,调用了spi_register_master函数,该函数将完成SPI控制器的注册,其中还牵涉到spi_device的注册.我们来看看这个函数.下列函数位于drivers/spi/spi.c:
1 int spi_register_master(struct spi_master *master) 2 { 3 static atomic_t dyn_bus_id = ATOMIC_INIT((1<<15) - 1); 4 struct device *dev = master->dev.parent; 5 struct boardinfo *bi; 6 int status = -ENODEV; 7 int dynamic = 0; 8 9 if (!dev) 10 return -ENODEV; 11 12 status = of_spi_register_master(master); 13 if (status) 14 return status; 15 16 /* even if it's just one always-selected device, there must 17 * be at least one chipselect 18 */ 19 if (master->num_chipselect == 0)/*SPI主控制器支持的片选数当然不能为0,否则还怎么挂接从设备啊.一个接口对应一个master,一个master对应 20 一条SPI总线,一条总线上可能挂有多个设备,num_chipselect就表示该总线上的设备数*/ 21 return -EINVAL; 22 23 if ((master->bus_num < 0) && master->dev.of_node) 24 master->bus_num = of_alias_get_id(master->dev.of_node, "spi"); 25 26 /* convention: dynamically assigned bus IDs count down from the max */ 27 if (master->bus_num < 0) {/*总线号从最大开始减*/ 28 /* FIXME switch to an IDR based scheme, something like 29 * I2C now uses, so we can't run out of "dynamic" IDs 30 */ 31 master->bus_num = atomic_dec_return(&dyn_bus_id); 32 dynamic = 1; 33 } 34 35 spin_lock_init(&master->bus_lock_spinlock); 36 mutex_init(&master->bus_lock_mutex); 37 master->bus_lock_flag = 0;/*这个标志指示SPI总线是否被锁*/ 38 39 /* register the device, then userspace will see it. 40 * registration fails if the bus ID is in use. 41 */ 42 dev_set_name(&master->dev, "spi%u", master->bus_num); 43 status = device_add(&master->dev);/*向内核注册设备*/ 44 if (status < 0) 45 goto done; 46 dev_dbg(dev, "registered master %s%s ", dev_name(&master->dev), 47 dynamic ? " (dynamic)" : ""); 48 49 /* If we're using a queued driver, start the queue */ 50 if (master->transfer)/*对于具体到davinci,此字段在spi_bitbang_start中被初始化为spi_bitbang_transfer*/ 51 dev_info(dev, "master is unqueued, this is deprecated "); 52 else { 53 status = spi_master_initialize_queue(master); 54 if (status) { 55 device_unregister(&master->dev); 56 goto done; 57 } 58 } 59 60 mutex_lock(&board_lock); 61 list_add_tail(&master->list, &spi_master_list);/*把这个SPI主机控制器添加进全局的spi_master_list链表*/ 62 list_for_each_entry(bi, &board_list, list)/*遍历全局的board_list链表,为每一个boardinfo结构节点查找其中的指向的spi_board_info结构,通过 63 对spi_board_info的bus_bum和SPI主机控制器(spi_master)的bus_num进行匹配,来确定SPI从设备是否由此SPI主机控制器来控制.如果匹配,则通 64 过调用spi_new_device函数创建spi_device从设备,并且将其注册进内核*/ 65 spi_match_master_to_boardinfo(master, &bi->board_info); 66 mutex_unlock(&board_lock); 67 68 /* Register devices from the device tree and ACPI */ 69 of_register_spi_devices(master); 70 acpi_register_spi_devices(master); 71 done: 72 return status; 73 } 74 EXPORT_SYMBOL_GPL(spi_register_master);
该函数注释一目了然,我们来看看spi_match_master_to_boardinfo这个函数吧.在同文件中有:
1 /*使用SPI主控制类和板级信息匹配则添加一个新设备*/ 2 static void spi_match_master_to_boardinfo(struct spi_master *master, 3 struct spi_board_info *bi) 4 { 5 struct spi_device *dev; 6 7 if (master->bus_num != bi->bus_num)/*通过bus_num对spi设备和master进行匹配*/ 8 return; 9 10 dev = spi_new_device(master, bi);/*执行到此,表示匹配完成,SPI设备由该SPI接口来控制,开始创建spi_device*/ 11 if (!dev) 12 dev_err(master->dev.parent, "can't create new device for %s ", 13 bi->modalias); 14 }
地球人都知道这段代码什么意思,好了继续看spi_new_device函数.在同文件中:
1 struct spi_device *spi_new_device(struct spi_master *master, 2 struct spi_board_info *chip) 3 { 4 struct spi_device *proxy; 5 int status; 6 7 /* NOTE: caller did any chip->bus_num checks necessary. 8 * 9 * Also, unless we change the return value convention to use 10 * error-or-pointer (not NULL-or-pointer), troubleshootability 11 * suggests syslogged diagnostics are best here (ugh). 12 */ 13 14 proxy = spi_alloc_device(master);/*分配spi_device结构,并初始化一些字段*/ 15 if (!proxy) 16 return NULL; 17 18 WARN_ON(strlen(chip->modalias) >= sizeof(proxy->modalias)); 19 20 /*从spi_board_info获取SPI从设备的参数*/ 21 proxy->chip_select = chip->chip_select; 22 proxy->max_speed_hz = chip->max_speed_hz; 23 proxy->mode = chip->mode; 24 proxy->irq = chip->irq; 25 strlcpy(proxy->modalias, chip->modalias, sizeof(proxy->modalias)); 26 proxy->dev.platform_data = (void *) chip->platform_data; 27 proxy->controller_data = chip->controller_data; 28 proxy->controller_state = NULL; 29 30 status = spi_add_device(proxy);/*将新设备添加进内核*/ 31 if (status < 0) { 32 spi_dev_put(proxy);/*从内核模块中撤销这个SPI(从)设备,但是这貌似并没有释放spi_alloc_device开辟的内存.实质上这个函数只是减少 33 了SPI(从)设备的引用计数*/ 34 return NULL; 35 } 36 37 return proxy; 38 } 39 EXPORT_SYMBOL_GPL(spi_new_device);
这个函数首先创建了spi_device结构,让后通过板级信息spi_board_info将SPI从设备的相关信息复制给spi_device结构,从而完成了spi_device结构的定义,最后调用spi_add_device,完成spi_device的注册.其中struct spi_board_info *chip这就是我们当初arch/arm/mach-davinci/board-dm365-evm.c中定义的dm365_evm_spi_info数组中的结构实例.
第25行我们就知道,这里注册的spi_device的modalias字段就被初始化为"at25".那么与其对应的spi_driver的device_driver中的name字段肯定为"at25".只有这样才能在SPI核心层的spi_match_device函数中匹配.搜了一遍内核,看到在drivers/msic/eeprom/at25.c中有:
1 static struct spi_driver at25_driver = { 2 .driver = { 3 .name = "at25", 4 .owner = THIS_MODULE, 5 }, 6 .probe = at25_probe,/*与相应的SPI(从)设备spi_device匹配成功后,则调用这里的probe函数*/ 7 .remove = at25_remove, 8 }; 9 10 module_spi_driver(at25_driver);
第10行这个宏是SPI架构专门定义的,在include/linux/spi/spi.h中,我们来看:
1 #define module_spi_driver(__spi_driver) 2 module_driver(__spi_driver, spi_register_driver, 3 spi_unregister_driver)
让暴风雨来的更猛烈些吧,研究内核的孩纸都伤不起啊,我们只有硬着头皮往下看,在include/linux/device.h中:
1 #define module_driver(__driver, __register, __unregister, ...) 2 static int __init __driver##_init(void) 3 { 4 return __register(&(__driver) , ##__VA_ARGS__); 5 } 6 module_init(__driver##_init); 7 static void __exit __driver##_exit(void) 8 { 9 __unregister(&(__driver) , ##__VA_ARGS__); 10 } 11 module_exit(__driver##_exit);
山重水复疑无路,柳暗花明又一村.这东东你让我说啥~没说的.相信大家也不想在听我唠叨.但是这里为什么多此一举写了这么一个叫宏,而不是像其他的linux模块那样直接写两个module_xxx呢?这是因为这个设备eeprom本身是不可插拔的,也就不需要什么加载卸载的过程,系统上电运行直接就注册了.
那么我们知道了,现在因为SPI子系统核心层我们已经注册了一条SPI总线,就是spi_bus_type.它里面的match回调函数我们已经看过了,就是spi_match_device.就是在这个函数中将完成这个spi_device和spi_driver的匹配,匹配成功就会去执行spi_driver的probe回调了.我们来看,at25_probe函数在drivers/msic/eeprom/at25.c中:
1 static int at25_probe(struct spi_device *spi) 2 { 3 struct at25_data *at25 = NULL;/*这个结构其实就是对spi_device的封装,我们可以像理解面向对象那样将这个结构理解为对spi_device的实例*/ 4 struct spi_eeprom chip;/*此结构用来作为记录一个SPI EEPROMS的句柄,它保存了platform_data的数据*/ 5 struct device_node *np = spi->dev.of_node; 6 int err; 7 int sr; 8 int addrlen; 9 10 /* Chip description */ 11 if (!spi->dev.platform_data) {/*具体到dm365平台,此platform_data就是arch/arm/mach-davinci/board-ddm365-evm.c中定义的的at25640*/ 12 if (np) { 13 err = at25_np_to_chip(&spi->dev, np, &chip); 14 if (err) 15 goto fail; 16 } else { 17 dev_err(&spi->dev, "Error: no chip description "); 18 err = -ENODEV; 19 goto fail; 20 } 21 } else 22 chip = *(struct spi_eeprom *)spi->dev.platform_data; 23 24 /* For now we only support 8/16/24 bit addressing */ 25 if (chip.flags & EE_ADDR1)/*flags用来标志eeprom的位宽和读写模式,具体到dm365平台此flags为EE_ADDR2*/ 26 addrlen = 1; 27 else if (chip.flags & EE_ADDR2) 28 addrlen = 2; 29 else if (chip.flags & EE_ADDR3) 30 addrlen = 3; 31 else { 32 dev_dbg(&spi->dev, "unsupported address type "); 33 err = -EINVAL; 34 goto fail; 35 } 36 37 /* Ping the chip ... the status register is pretty portable, 38 * unlike probing manufacturer IDs. We do expect that system 39 * firmware didn't write it in the past few milliseconds! 40 */ 41 /*ping一下芯片,状态寄存器是很容易被检测的,不像制造商ID那样麻烦.我们期待系统固件之前没有写入它.*/ 42 sr = spi_w8r8(spi, AT25_RDSR);/*同步的读取状态寄存器的值,返回的八位数据保存在sr中.spi_w8r8这个函数有可能会睡眠*/ 43 if (sr < 0 || sr & AT25_SR_nRDY) { 44 dev_dbg(&spi->dev, "rdsr --> %d (%02x) ", sr, sr); 45 err = -ENXIO; 46 goto fail; 47 } 48 49 if (!(at25 = kzalloc(sizeof *at25, GFP_KERNEL))) {/*以kmalloc分配内存,并清0*/ 50 err = -ENOMEM; 51 goto fail; 52 } 53 54 mutex_init(&at25->lock);/*初始化互斥体*/ 55 at25->chip = chip;/*记录下spi_eeprom*/ 56 at25->spi = spi_dev_get(spi);/*记录下这个片子对应的spi_device*/ 57 dev_set_drvdata(&spi->dev, at25);/*spi->dev.device_private->driver_data = at25*/ 58 at25->addrlen = addrlen;/*我觉得应该可以理解为这个片子使用的位宽是多少个字节.那根据上文分析,此处值为2*/ 59 60 /* Export the EEPROM bytes through sysfs, since that's convenient. 61 * And maybe to other kernel code; it might hold a board's Ethernet 62 * address, or board-specific calibration data generated on the 63 * manufacturing floor. 64 * 65 * Default to root-only access to the data; EEPROMs often hold data 66 * that's sensitive for read and/or write, like ethernet addresses, 67 * security codes, board-specific manufacturing calibrations, etc. 68 */ 69 /*通过sysfs文件系统导出EEPROM的字节,因为这是很方便的.也许其他内核代码也是这样做的:比如保存板子的以太网地址,或者是生产商的特定板的校验数据. 70 默认只有root用户能够访问的数据.EEPROMs经常保存一些敏感的读或写的数据,像是以太网地址,安全码,特定板的校准数据等*/ 71 sysfs_bin_attr_init(&at25->bin);/*初始化一个动态分配的bin_attribute属性*/ 72 at25->bin.attr.name = "eeprom";/*属性的名字*/ 73 at25->bin.attr.mode = S_IRUSR;/*属性的模式(用户可读)*/ 74 at25->bin.read = at25_bin_read;/*属性的读方法*/ 75 at25->mem.read = at25_mem_read;/*片子的内存读函数*/ 76 77 at25->bin.size = at25->chip.byte_len; 78 if (!(chip.flags & EE_READONLY)) {/*flags用来标志eeprom的位宽和读写模式,具体到dm365平台此flags为EE_ADDR2*/ 79 at25->bin.write = at25_bin_write;/*如果eeprom片子不是只读的话,那么就设置属性的写方法*/ 80 at25->bin.attr.mode |= S_IWUSR;/*增加属性的模式(用户可写)*/ 81 at25->mem.write = at25_mem_write;/*片子的内存写函数*/ 82 } 83 84 err = sysfs_create_bin_file(&spi->dev.kobj, &at25->bin);/*创建一个二进制的属性文件*/ 85 if (err) 86 goto fail; 87 88 if (chip.setup)/*如果片子定义了setup函数,具体到dm365平台,此platform_data就是arch/arm/mach-davinci/board-ddm365-evm.c中定义的的at25640里并没有 89 定义这个函数,因此为空*/ 90 chip.setup(&at25->mem, chip.context);/*使用片子的setup函数做一些初始化*/ 91 92 dev_info(&spi->dev, "%Zd %s %s eeprom%s, pagesize %u ", 93 (at25->bin.size < 1024) 94 ? at25->bin.size 95 : (at25->bin.size / 1024), 96 (at25->bin.size < 1024) ? "Byte" : "KByte", 97 at25->chip.name, 98 (chip.flags & EE_READONLY) ? " (readonly)" : "", 99 at25->chip.page_size); 100 return 0; 101 fail: 102 dev_dbg(&spi->dev, "probe err %d ", err); 103 kfree(at25); 104 return err; 105 }
根据代码就能知道,这个spi_device实际上对应的是一个eeprom,而这里就是它的操作的一些初始化.也就是说,对于分析的这个davinci代码的实例,是dm365平台的,其开发板上应该是将eeprom通过spi总线挂接在了spi_master上.也就是挂接在了SOC上,因为我们的dm365片子本身就集成了spi_master.之后要访问eeprom其实回调最终的都是这里提供的一些接口.听起来有点黏糊,看个图吧:
哎,就写到这里,本人不会用visio,画个这图画了一下午~丢人啊!