spi 自带驱动spidev.c 的测试使用

1. Linux 提供了一个功能有限的 SPI 用户接口，如果不需要用到 IRQ 或者其他内核驱动接口，可以考虑使用接口 spidev 编写用户层程序控制 SPI 设备。代码在kernel\drivers\spi\spidev.c。

注册部分代码如下：

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,
};



/*-------------------------------------------------------------------------*/

/* The main reason to have this class is to make mdev/udev create the
 * /dev/spidevB.C character device nodes exposing our userspace API.
 * It also simplifies memory management.
 */

static struct class *spidev_class;

#ifdef CONFIG_OF
static const struct of_device_id spidev_dt_ids[] = {
	{ .compatible = "rohm,dh2228fv" },
	{ .compatible = "lineartechnology,ltc2488" },
	{ .compatible = "hoziron,j2" },
	{ .compatible = "barrot,i2224e" },
	{},
};
MODULE_DEVICE_TABLE(of, spidev_dt_ids);
#endif

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.
	 */
	if (spi->dev.of_node && !of_match_device(spidev_dt_ids, &spi->dev)) {
		dev_err(&spi->dev, "buggy DT: spidev listed directly in DT\n");
		WARN_ON(spi->dev.of_node &&
			!of_match_device(spidev_dt_ids, &spi->dev));
	}

	dev_err(&spi->dev, "zsm into spidev_probe!\n");

	/* 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) {
		struct device *dev;

		spidev->devt = MKDEV(SPIDEV_MAJOR, minor);
		dev = device_create(spidev_class, &spi->dev, spidev->devt,
				    spidev, "spidev%d.%d",
				    spi->master->bus_num, spi->chip_select);

		dev_err(&spi->dev, "zsm: spidev%d.%d\n", 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;

	if (status == 0)
		spi_set_drvdata(spi, spidev);
	else
		kfree(spidev);

	dev_err(&spi->dev, "zsm into spidev_probe over!\n");

	return status;
}

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

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

	/* prevent new opens */
	mutex_lock(&device_list_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;
}

static struct spi_driver spidev_spi_driver = {
	.driver = {
		.name =		"spidev",
		.of_match_table = of_match_ptr(spidev_dt_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.
	 */
};

/*-------------------------------------------------------------------------*/

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_zsm", &spidev_fops);
	if (status < 0)
		return status;

	spidev_class = class_create(THIS_MODULE, "spidev_zsm");
	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);
	if (status < 0) {
		class_destroy(spidev_class);
		unregister_chrdev(SPIDEV_MAJOR, spidev_spi_driver.driver.name);
	}
	return status;
}
module_init(spidev_init);

static void __exit spidev_exit(void)
{
	spi_unregister_driver(&spidev_spi_driver);
	class_destroy(spidev_class);
	unregister_chrdev(SPIDEV_MAJOR, spidev_spi_driver.driver.name);
}
module_exit(spidev_exit);

MODULE_AUTHOR("Andrea Paterniani, ");
MODULE_DESCRIPTION("User mode SPI device interface");
MODULE_LICENSE("GPL");
MODULE_ALIAS("spi:spidev");

2. 从以上代码看，如果要让 probe 能够触发，需要在 dts 文件里，设置spi的参数：

&spi2 {
	ble_i2224e:ble_i2224e {
		compatible = "barrot,i2224e";
		reg = <0>;
		spi-max-frequency = <20000000>;
		status = "okay";
	};
};

&spi2 代表这个设备挂载到了 spi2 总线上。

3. 在应用层读写设备文件节点的方法：

    给应用层调用的有一组文件节点，注册代码如下：

    #define SPIDEV_MAJOR            153    /* assigned */ 
    #define N_SPI_MINORS            32    /* ... up to 256 */

    BUILD_BUG_ON(N_SPI_MINORS > 256);
    status = register_chrdev(SPIDEV_MAJOR, "spi_zsm", &spidev_fops);
    if (status < 0)
        return status;

系统运行后，可以通过 cat /proc/devices 来查看当前注册情况。

    console:/ # cat /proc/devices                                                  
        Character devices:
         ... ...
        153 spi_zsm

如果打算在应用层读写这个节点，需要手动创建一下这个文件节点；供使用；

创建方法： # mknod /dev/spi_zsm0 c 153 0   // 这个名字 spi_zsm0 可以不和上面注册的“spi_zsm”一样；它是根据设备号来找设备的，不是根据名字。

则测试时，直接使用 echo 或者 cat 就可以调用到上面的 spidev_write()函数以及 spidev_read()函数。