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。