二十一、spi驱动框架及驱动代码分析

一、spi驱动框架简介

 

• spi核心层

　　　　提供spi控制器驱动和设备驱动的注册方法、注销方法、spi通信硬件无关接口

• spi主机驱动

　　　　主要包含spi硬件体系结构中适配器（spi控制器）的控制，用于产生spi读写时序。

• spi设备驱动

　　　通过spi主机驱动与CPU交换数据。

 

 二、驱动源码分析

1、spidev.c

(1)初始化

static int __init spidev_init(void)
{
	int status;

	/* Claim our 256 reserved device numbers.  Then register a class
	 * that will key udev/mdev to add/remove /dev nodes.  Last, register
	 * the driver which manages those device numbers.
	 */
	BUILD_BUG_ON(N_SPI_MINORS > 256);
	status = register_chrdev(SPIDEV_MAJOR, "spi", &spidev_fops);  //注册字符设备
	if (status < 0)
		return status;

	spidev_class = class_create(THIS_MODULE, "spidev");  //创建设备类
	if (IS_ERR(spidev_class)) {
		unregister_chrdev(SPIDEV_MAJOR, spidev_spi_driver.driver.name);
		return PTR_ERR(spidev_class);
	}

	status = spi_register_driver(&spidev_spi_driver);  //注册spi驱动
	if (status < 0) {
		class_destroy(spidev_class);
		unregister_chrdev(SPIDEV_MAJOR, spidev_spi_driver.driver.name);
	}
	return status;
}

（2)spi驱动定义

static struct spi_driver spidev_spi_driver = {
	.driver = {
		.name =		"spidev",
		.of_match_table = of_match_ptr(spidev_dt_ids),
		.acpi_match_table = ACPI_PTR(spidev_acpi_ids),
	},
	.probe =	spidev_probe,
	.remove =	spidev_remove,

	/* NOTE:  suspend/resume methods are not necessary here.
	 * We don't do anything except pass the requests to/from
	 * the underlying controller.  The refrigerator handles
	 * most issues; the controller driver handles the rest.
	 */
};

（3）spidev_probe　　

static int spidev_probe(struct spi_device *spi)
{
	struct spidev_data	*spidev;
	int			status;
	unsigned long		minor;

	/*
	 * spidev should never be referenced in DT without a specific
	 * compatible string, it is a Linux implementation thing
	 * rather than a description of the hardware.
	 */
	WARN(spi->dev.of_node &&
	     of_device_is_compatible(spi->dev.of_node, "spidev"),
	     "%pOF: buggy DT: spidev listed directly in DT\n", spi->dev.of_node);

	spidev_probe_acpi(spi);

	/* Allocate driver data */
	spidev = kzalloc(sizeof(*spidev), GFP_KERNEL);
	if (!spidev)
		return -ENOMEM;

	/* Initialize the driver data */
	spidev->spi = spi;
	spin_lock_init(&spidev->spi_lock);
	mutex_init(&spidev->buf_lock);

	INIT_LIST_HEAD(&spidev->device_entry);

	/* If we can allocate a minor number, hook up this device.
	 * Reusing minors is fine so long as udev or mdev is working.
	 */
	mutex_lock(&device_list_lock);
	minor = find_first_zero_bit(minors, N_SPI_MINORS);
	if (minor < N_SPI_MINORS) {  //次设备号小于32
		struct device *dev;

		spidev->devt = MKDEV(SPIDEV_MAJOR, minor);
　　　　　　　　　　//创建spi设备
		dev = device_create(spidev_class, &spi->dev, spidev->devt,
				    spidev, "spidev%d.%d",
				    spi->master->bus_num, spi->chip_select);
		status = PTR_ERR_OR_ZERO(dev);
	} else {
		dev_dbg(&spi->dev, "no minor number available!\n");
		status = -ENODEV;
	}
	if (status == 0) {
		set_bit(minor, minors);
		list_add(&spidev->device_entry, &device_list);
	}
	mutex_unlock(&device_list_lock);

	spidev->speed_hz = spi->max_speed_hz;   //设置最大速率

	if (status == 0)
		spi_set_drvdata(spi, spidev);  //设置设备驱动数据
	else
		kfree(spidev);

	return status;
}

（4）spidev_remove

static int spidev_remove(struct spi_device *spi)
{
	struct spidev_data	*spidev = spi_get_drvdata(spi);

	/* prevent new opens */
	mutex_lock(&device_list_lock);
	/* make sure ops on existing fds can abort cleanly */
	spin_lock_irq(&spidev->spi_lock);
	spidev->spi = NULL;
	spin_unlock_irq(&spidev->spi_lock);

	list_del(&spidev->device_entry);
	device_destroy(spidev_class, spidev->devt);
	clear_bit(MINOR(spidev->devt), minors);
	if (spidev->users == 0)
		kfree(spidev);
	mutex_unlock(&device_list_lock);

	return 0;
}

(5)spi设备文件操作集合

static const struct file_operations spidev_fops = {
	.owner =	THIS_MODULE,
	/* REVISIT switch to aio primitives, so that userspace
	 * gets more complete API coverage.  It'll simplify things
	 * too, except for the locking.
	 */
	.write =	spidev_write,
	.read =		spidev_read,
	.unlocked_ioctl = spidev_ioctl,
	.compat_ioctl = spidev_compat_ioctl,
	.open =		spidev_open,
	.release =	spidev_release,
	.llseek =	no_llseek,
};

（6）读操作

/* Read-only message with current device setup */
static ssize_t
spidev_read(struct file *filp, char __user *buf, size_t count, loff_t *f_pos)
{
	struct spidev_data	*spidev;
	ssize_t			status = 0;

	/* chipselect only toggles at start or end of operation */
	if (count > bufsiz)
		return -EMSGSIZE;

	spidev = filp->private_data;

	mutex_lock(&spidev->buf_lock);
	status = spidev_sync_read(spidev, count);
	if (status > 0) {
		unsigned long	missing;

		missing = copy_to_user(buf, spidev->rx_buffer, status);
		if (missing == status)
			status = -EFAULT;
		else
			status = status - missing;
	}
	mutex_unlock(&spidev->buf_lock);

	return status;
}　

spidev_sync_read：

static inline ssize_t
spidev_sync_read(struct spidev_data *spidev, size_t len)
{
	struct spi_transfer	t = {
			.rx_buf		= spidev->rx_buffer,
			.len		= len,
			.speed_hz	= spidev->speed_hz,
		};
	struct spi_message	m;

	spi_message_init(&m);
	spi_message_add_tail(&t, &m);
	return spidev_sync(spidev, &m);
}

（7）写操作

/* Write-only message with current device setup */
static ssize_t
spidev_write(struct file *filp, const char __user *buf,
		size_t count, loff_t *f_pos)
{
	struct spidev_data	*spidev;
	ssize_t			status = 0;
	unsigned long		missing;

	/* chipselect only toggles at start or end of operation */
	if (count > bufsiz)
		return -EMSGSIZE;

	spidev = filp->private_data;

	mutex_lock(&spidev->buf_lock);
	missing = copy_from_user(spidev->tx_buffer, buf, count);
	if (missing == 0)
		status = spidev_sync_write(spidev, count);
	else
		status = -EFAULT;
	mutex_unlock(&spidev->buf_lock);

	return status;
}

spidev_sync_write：

static inline ssize_t
spidev_sync_write(struct spidev_data *spidev, size_t len)
{
	struct spi_transfer	t = {
			.tx_buf		= spidev->tx_buffer,
			.len		= len,
			.speed_hz	= spidev->speed_hz,
		};
	struct spi_message	m;

	spi_message_init(&m);
	spi_message_add_tail(&t, &m);
	return spidev_sync(spidev, &m);
}

（8）spidev_ioctl

static long
spidev_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
{
	int			retval = 0;
	struct spidev_data	*spidev;
	struct spi_device	*spi;
	u32			tmp;
	unsigned		n_ioc;
	struct spi_ioc_transfer	*ioc;

	/* Check type and command number */
	if (_IOC_TYPE(cmd) != SPI_IOC_MAGIC)
		return -ENOTTY;

	/* guard against device removal before, or while,
	 * we issue this ioctl.
	 */
	spidev = filp->private_data;
	spin_lock_irq(&spidev->spi_lock);
	spi = spi_dev_get(spidev->spi);
	spin_unlock_irq(&spidev->spi_lock);

	if (spi == NULL)
		return -ESHUTDOWN;

	/* use the buffer lock here for triple duty:
	 *  - prevent I/O (from us) so calling spi_setup() is safe;
	 *  - prevent concurrent SPI_IOC_WR_* from morphing
	 *    data fields while SPI_IOC_RD_* reads them;
	 *  - SPI_IOC_MESSAGE needs the buffer locked "normally".
	 */
	mutex_lock(&spidev->buf_lock);

	switch (cmd) {
	/* read requests */读取spi的属性
	case SPI_IOC_RD_MODE:   //读取spi mode
		retval = put_user(spi->mode & SPI_MODE_MASK,
					(__u8 __user *)arg);
		break;
	case SPI_IOC_RD_MODE32:
		retval = put_user(spi->mode & SPI_MODE_MASK,
					(__u32 __user *)arg);
		break;
	case SPI_IOC_RD_LSB_FIRST:  //读取spi是低位优先还是高位优先
		retval = put_user((spi->mode & SPI_LSB_FIRST) ?  1 : 0,
					(__u8 __user *)arg);
		break;
	case SPI_IOC_RD_BITS_PER_WORD:   //读取每个字 的bit位数
		retval = put_user(spi->bits_per_word, (__u8 __user *)arg);
		break;
	case SPI_IOC_RD_MAX_SPEED_HZ:  //最大速率
		retval = put_user(spidev->speed_hz, (__u32 __user *)arg);
		break;

	/* write requests */  这是对应的写，用于设置spi属性
	case SPI_IOC_WR_MODE:
	case SPI_IOC_WR_MODE32:
		if (cmd == SPI_IOC_WR_MODE)
			retval = get_user(tmp, (u8 __user *)arg);
		else
			retval = get_user(tmp, (u32 __user *)arg);
		if (retval == 0) {
			struct spi_controller *ctlr = spi->controller;
			u32	save = spi->mode;

			if (tmp & ~SPI_MODE_MASK) {
				retval = -EINVAL;
				break;
			}

			if (ctlr->use_gpio_descriptors && ctlr->cs_gpiods &&
			    ctlr->cs_gpiods[spi->chip_select])
				tmp |= SPI_CS_HIGH;

			tmp |= spi->mode & ~SPI_MODE_MASK;
			spi->mode = (u16)tmp;
			retval = spi_setup(spi);
			if (retval < 0)
				spi->mode = save;
			else
				dev_dbg(&spi->dev, "spi mode %x\n", tmp);
		}
		break;
	case SPI_IOC_WR_LSB_FIRST:
		retval = get_user(tmp, (__u8 __user *)arg);
		if (retval == 0) {
			u32	save = spi->mode;

			if (tmp)
				spi->mode |= SPI_LSB_FIRST;
			else
				spi->mode &= ~SPI_LSB_FIRST;
			retval = spi_setup(spi);
			if (retval < 0)
				spi->mode = save;
			else
				dev_dbg(&spi->dev, "%csb first\n",
						tmp ? 'l' : 'm');
		}
		break;
	case SPI_IOC_WR_BITS_PER_WORD:
		retval = get_user(tmp, (__u8 __user *)arg);
		if (retval == 0) {
			u8	save = spi->bits_per_word;

			spi->bits_per_word = tmp;
			retval = spi_setup(spi);
			if (retval < 0)
				spi->bits_per_word = save;
			else
				dev_dbg(&spi->dev, "%d bits per word\n", tmp);
		}
		break;
	case SPI_IOC_WR_MAX_SPEED_HZ:
		retval = get_user(tmp, (__u32 __user *)arg);
		if (retval == 0) {
			u32	save = spi->max_speed_hz;

			spi->max_speed_hz = tmp;
			retval = spi_setup(spi);
			if (retval >= 0)
				spidev->speed_hz = tmp;
			else
				dev_dbg(&spi->dev, "%d Hz (max)\n", tmp);
			spi->max_speed_hz = save;
		}
		break;

	default:
		/* segmented and/or full-duplex I/O request */
		/* Check message and copy into scratch area */
		ioc = spidev_get_ioc_message(cmd,
				(struct spi_ioc_transfer __user *)arg, &n_ioc);
		if (IS_ERR(ioc)) {
			retval = PTR_ERR(ioc);
			break;
		}
		if (!ioc)
			break;	/* n_ioc is also 0 */

		/* translate to spi_message, execute */
		retval = spidev_message(spidev, ioc, n_ioc);
		kfree(ioc);
		break;
	}

	mutex_unlock(&spidev->buf_lock);
	spi_dev_put(spi);
	return retval;
}

　　

2、spi平台驱动程序分析：spi_sun6i.c

(1)平台驱动定义

static const struct dev_pm_ops sun6i_spi_pm_ops = {
	.runtime_resume		= sun6i_spi_runtime_resume,
	.runtime_suspend	= sun6i_spi_runtime_suspend,
};

static struct platform_driver sun6i_spi_driver = {
	.probe	= sun6i_spi_probe,
	.remove	= sun6i_spi_remove,
	.driver	= {
		.name		= "sun6i-spi",
		.of_match_table	= sun6i_spi_match,
		.pm		= &sun6i_spi_pm_ops,
	},
}

（2）sun6i_spi_probe

static int sun6i_spi_probe(struct platform_device *pdev)
{
	struct spi_master *master;
	struct sun6i_spi *sspi;
	int ret = 0, irq;

	master = spi_alloc_master(&pdev->dev, sizeof(struct sun6i_spi));
	if (!master) {
		dev_err(&pdev->dev, "Unable to allocate SPI Master\n");
		return -ENOMEM;
	}

	platform_set_drvdata(pdev, master);
	sspi = spi_master_get_devdata(master);
         //获取平台设备的io资源
	sspi->base_addr = devm_platform_ioremap_resource(pdev, 0);
	if (IS_ERR(sspi->base_addr)) {
		ret = PTR_ERR(sspi->base_addr);
		goto err_free_master;
	}
       //获取irq资源
	irq = platform_get_irq(pdev, 0);
	if (irq < 0) {
		ret = -ENXIO;
		goto err_free_master;
	}
        //申请中断
	ret = devm_request_irq(&pdev->dev, irq, sun6i_spi_handler,
			       0, "sun6i-spi", sspi);
	if (ret) {
		dev_err(&pdev->dev, "Cannot request IRQ\n");
		goto err_free_master;
	}

	sspi->master = master;
	sspi->fifo_depth = (unsigned long)of_device_get_match_data(&pdev->dev);

    //spi主机的初始化
	master->max_speed_hz = 100 * 1000 * 1000;   //spi主机最大速率 100Mhz
	master->min_speed_hz = 3 * 1000;　　　　　　　//spi主机最小速率3000hz　
	master->set_cs = sun6i_spi_set_cs;          //设置片选引脚信号
	master->transfer_one = sun6i_spi_transfer_one;  //发送一个spi消息
	master->num_chipselect = 4;     //有4个片选信号
	master->mode_bits = SPI_CPOL | SPI_CPHA | SPI_CS_HIGH | SPI_LSB_FIRST;   //spi模式
	master->bits_per_word_mask = SPI_BPW_MASK(8);  //发送一个字8个字节
	master->dev.of_node = pdev->dev.of_node;     //设备节点
	master->auto_runtime_pm = true;
	master->max_transfer_size = sun6i_spi_max_transfer_size;  //最多发送的字节个数  0xffffff-1

	sspi->hclk = devm_clk_get(&pdev->dev, "ahb");    //获取AHB总线的clk
	if (IS_ERR(sspi->hclk)) {
		dev_err(&pdev->dev, "Unable to acquire AHB clock\n");
		ret = PTR_ERR(sspi->hclk);
		goto err_free_master;
	}

	sspi->mclk = devm_clk_get(&pdev->dev, "mod");   //获取模块clock
	if (IS_ERR(sspi->mclk)) {
		dev_err(&pdev->dev, "Unable to acquire module clock\n");
		ret = PTR_ERR(sspi->mclk);
		goto err_free_master;
	}

	init_completion(&sspi->done);
//获取复位控制器
	sspi->rstc = devm_reset_control_get_exclusive(&pdev->dev, NULL);
	if (IS_ERR(sspi->rstc)) {
		dev_err(&pdev->dev, "Couldn't get reset controller\n");
		ret = PTR_ERR(sspi->rstc);
		goto err_free_master;
	}

	/*
	 * This wake-up/shutdown pattern is to be able to have the
	 * device woken up, even if runtime_pm is disabled
	 */
           //恢复spi设备 
	ret = sun6i_spi_runtime_resume(&pdev->dev);
	if (ret) {
		dev_err(&pdev->dev, "Couldn't resume the device\n");
		goto err_free_master;
	}

	pm_runtime_set_active(&pdev->dev);
	pm_runtime_enable(&pdev->dev);
	pm_runtime_idle(&pdev->dev);
       //注册spi主机
	ret = devm_spi_register_master(&pdev->dev, master);
	if (ret) {
		dev_err(&pdev->dev, "cannot register SPI master\n");
		goto err_pm_disable;
	}

	return 0;

err_pm_disable:
	pm_runtime_disable(&pdev->dev);
	sun6i_spi_runtime_suspend(&pdev->dev);
err_free_master:
	spi_master_put(master);
	return ret;
}　

 

• sun6i_spi_remove

static int sun6i_spi_remove(struct platform_device *pdev)
{
     //强制挂机
	pm_runtime_force_suspend(&pdev->dev);

	return 0;
}　

 

• sun6i_spi_match

static const struct of_device_id sun6i_spi_match[] = {
	{ .compatible = "allwinner,sun6i-a31-spi", .data = (void *)SUN6I_FIFO_DEPTH },
	{ .compatible = "allwinner,sun8i-h3-spi",  .data = (void *)SUN8I_FIFO_DEPTH },
	{}
};

(3)spi_device结构体

//spi.h
struct spi_device {
	struct device		dev;      //spi设备
	struct spi_controller	*controller;    //spi控制器
	struct spi_controller	*master;	/* compatibility layer */ spi的 复制，为了向后兼容
	u32			max_speed_hz;  
	u8			chip_select;    //Chipselect, distinguishing chips
	u8			bits_per_word;  //定义每个字的bits位数，由spi协议决定
	bool			rt;  //使pump线程实时优先
	u32			mode;   //spi模式
#define	SPI_CPHA	0x01			/* clock phase */
#define	SPI_CPOL	0x02			/* clock polarity */
#define	SPI_MODE_0	(0|0)			/* (original MicroWire) */
#define	SPI_MODE_1	(0|SPI_CPHA)
#define	SPI_MODE_2	(SPI_CPOL|0)
#define	SPI_MODE_3	(SPI_CPOL|SPI_CPHA)
#define	SPI_CS_HIGH	0x04			/* chipselect active high? */
#define	SPI_LSB_FIRST	0x08			/* per-word bits-on-wire */
#define	SPI_3WIRE	0x10			/* SI/SO signals shared */
#define	SPI_LOOP	0x20			/* loopback mode */
#define	SPI_NO_CS	0x40			/* 1 dev/bus, no chipselect */
#define	SPI_READY	0x80			/* slave pulls low to pause */
#define	SPI_TX_DUAL	0x100			/* transmit with 2 wires */
#define	SPI_TX_QUAD	0x200			/* transmit with 4 wires */
#define	SPI_RX_DUAL	0x400			/* receive with 2 wires */
#define	SPI_RX_QUAD	0x800			/* receive with 4 wires */
#define	SPI_CS_WORD	0x1000			/* toggle cs after each word */
#define	SPI_TX_OCTAL	0x2000			/* transmit with 8 wires */
#define	SPI_RX_OCTAL	0x4000			/* receive with 8 wires */
#define	SPI_3WIRE_HIZ	0x8000			/* high impedance turnaround */
	int			irq;    //中断号
	void			*controller_state;   //控制器的实时状态
	void			*controller_data;
	char			modalias[SPI_NAME_SIZE];  //驱动别名
	const char		*driver_override;
	int			cs_gpio;	/* LEGACY: chip select gpio */
	struct gpio_desc	*cs_gpiod;	/* chip select gpio desc */
	uint8_t			word_delay_usecs; //每个字数据之间的微秒延时

	/* the statistics */
	struct spi_statistics	statistics;  //spi传输的统计信息，包括传输的数据信息

	/*
	 * likely need more hooks for more protocol options affecting how
	 * the controller talks to each chip, like:
	 *  - memory packing (12 bit samples into low bits, others zeroed)
	 *  - priority
	 *  - chipselect delays
	 *  - ...
	 */
};　

2、spi.c

（1）spi_init

//spi.c
static int __init spi_init(void)
{
	int	status;

	buf = kmalloc(SPI_BUFSIZ, GFP_KERNEL);
	if (!buf) {
		status = -ENOMEM;
		goto err0;
	}

	status = bus_register(&spi_bus_type);   //总线注册，注册后，可以在/sys/bus目录下看到注册的总线
	if (status < 0)
		goto err1;
      //注册spi主机类
	status = class_register(&spi_master_class);  //
	if (status < 0)
		goto err2;
        //注册从机类
	if (IS_ENABLED(CONFIG_SPI_SLAVE)) {
		status = class_register(&spi_slave_class);
		if (status < 0)
			goto err3;
	}

	if (IS_ENABLED(CONFIG_OF_DYNAMIC))
		WARN_ON(of_reconfig_notifier_register(&spi_of_notifier));
	if (IS_ENABLED(CONFIG_ACPI))
		WARN_ON(acpi_reconfig_notifier_register(&spi_acpi_notifier));

	return 0;

err3:
	class_unregister(&spi_master_class);
err2:
	bus_unregister(&spi_bus_type);
err1:
	kfree(buf);
	buf = NULL;
err0:
	return status;
}

（2）spi_bus_type定义：

struct bus_type spi_bus_type = {
	.name		= "spi",    //总线名
	.dev_groups	= spi_dev_groups,  //设备组
	.match		= spi_match_device,   //spi匹配
	.uevent		= spi_uevent,  
};　

• spi_match_device :spi设备和驱动的匹配方式， 

static int spi_match_device(struct device *dev, struct device_driver *drv)
{
	const struct spi_device	*spi = to_spi_device(dev);
	const struct spi_driver	*sdrv = to_spi_driver(drv);
       //通过spi设备名和驱动名进行匹配
	/* Check override first, and if set, only use the named driver */
	if (spi->driver_override)
		return strcmp(spi->driver_override, drv->name) == 0;

	/* Attempt an OF style match */
	if (of_driver_match_device(dev, drv))  //设备树中compatiable属性和驱动名进行匹配
		return 1;

	/* Then try ACPI */
	if (acpi_driver_match_device(dev, drv))  //acpi匹配  
		return 1;

	if (sdrv->id_table)
		return !!spi_match_id(sdrv->id_table, spi);  //通过驱动别名来进行匹配

	return strcmp(spi->modalias, drv->name) == 0;
}

• spi_uevent

static int spi_uevent(struct device *dev, struct kobj_uevent_env *env)
{
	const struct spi_device		*spi = to_spi_device(dev);
	int rc;

	rc = acpi_device_uevent_modalias(dev, env);
	if (rc != -ENODEV)
		return rc;

	return add_uevent_var(env, "MODALIAS=%s%s", SPI_MODULE_PREFIX, spi->modalias);
}

（3）spi_master_class定义：

static struct class spi_master_class = {
	.name		= "spi_master",
	.owner		= THIS_MODULE,
	.dev_release	= spi_controller_release,
	.dev_groups	= spi_master_groups,
};

(4)spi驱动注册

/**
 * __spi_register_driver - register a SPI driver
 * @owner: owner module of the driver to register
 * @sdrv: the driver to register
 * Context: can sleep
 *
 * Return: zero on success, else a negative error code.
 */
int __spi_register_driver(struct module *owner, struct spi_driver *sdrv)
{
	sdrv->driver.owner = owner;
	sdrv->driver.bus = &spi_bus_type;
	sdrv->driver.probe = spi_drv_probe;
	sdrv->driver.remove = spi_drv_remove;
	if (sdrv->shutdown)
		sdrv->driver.shutdown = spi_drv_shutdown;
	return driver_register(&sdrv->driver);
}
EXPORT_SYMBOL_GPL(__spi_register_driver);　

　　

• spi_drv_probe

static int spi_drv_probe(struct device *dev)
{
	const struct spi_driver		*sdrv = to_spi_driver(dev->driver);
	struct spi_device		*spi = to_spi_device(dev);
	int ret;

	ret = of_clk_set_defaults(dev->of_node, false);   //获取设备树中的clock属性，并设置clock
	if (ret)
		return ret;

	if (dev->of_node) {
		spi->irq = of_irq_get(dev->of_node, 0);   //获取spi终端
		if (spi->irq == -EPROBE_DEFER)
			return -EPROBE_DEFER;
		if (spi->irq < 0)
			spi->irq = 0;
	}

	ret = dev_pm_domain_attach(dev, true);  //将spi设备加进PM域，用于节省电源能耗
	if (ret)
		return ret;

	if (sdrv->probe) {
		ret = sdrv->probe(spi);
		if (ret)
			dev_pm_domain_detach(dev, true);
	}

	return ret;
}　

Linux PM domain概述和使用流程

• spi_remove

static int spi_drv_remove(struct device *dev)
{
	const struct spi_driver		*sdrv = to_spi_driver(dev->driver);
	int ret = 0;

	if (sdrv->remove)
		ret = sdrv->remove(to_spi_device(dev));
	dev_pm_domain_detach(dev, true);  //spi驱动移除后，要将spi设备从pm域中去掉

	return ret;
}