SPI protocol驱动编写实例

内核版本:3.9.5

Linux中SPI驱动有俩个部分组成:controller驱动,直接和底层硬件打交道,protocol驱动,针对特定的设备,也是我们要做的.

这里只考虑SPI protocol驱动

在主线内核中有一个通用的字符型驱动范例spidev.本文不讨论spidev,而是探讨如何编写一个自定义SPI设备驱动.

为何要编写一个自定义驱动:

可以掌控性能;
无需给内核打补丁.SPI框架完整支持在可加载内核模块中进行驱动设置.这也就允许我们在内核源码树外进行编写代码;

Kernel Configuration

关掉SPIDEV选项以支持自定义的驱动

Device Drivers-->

SPI support-->

*** SPI Protocol Masters ***

<> User mode SPIdevice driver support

为使linuxSPI系统识别你的驱动,需要做两步准备.

1. 在特定的SPI总线(一个master就是一条总线)上注册SPI slave设备.可以是内核初始化的时候亦或是在你的驱动代码中动态的进行.设备名称在这步中必须指定;

2. 注册SPI protocol驱动.使用的名字必须和步骤1中的一致,这样kernel就可以将它们链接在一起了;

两个步骤可以以任意次序进行,但是得知道当他们完成之后,SPI框架就可以响应你驱动中的probe()调用了.你将得到一个spi_device用来和SPI系统进行交互了.一旦你的probe函数调用成功,你就可以开始使用SPI总线了.

静态注册SPI设备涵盖在spidev中了.

动态主册SPI设备的步骤如下:

1. 得到管理总线的spi_master控制器指针(句柄);

2. 为总线分配spi_device结构;

3. 验证没有其他的设备已经在这条总线bus.cs上注册过了;

4. 使用设备特定的值(speed,datasize,etc)来填充spi_device;

5. 将新的spi_device添加到总线;

有个范例代码:

 1 static int __init add_spike_device_to_bus(void)
 2 {
 3     struct spi_master *spi_master;
 4     struct spi_device *spi_device;
 5     struct device *pdev;
 6     char buff[64];
 7     int status = 0;
 8 
 9     spi_master = spi_busnum_to_master(SPI_BUS);
10     if (!spi_master) {
11         printk(KERN_ALERT "spi_busnum_to_master(%d) returned NULL\n",
12             SPI_BUS);
13         printk(KERN_ALERT "Missing modprobe omap2_mcspi?\n");
14         return -1;
15     }
16 
17     spi_device = spi_alloc_device(spi_master);
18     if (!spi_device) {
19         put_device(&spi_master->dev);
20         printk(KERN_ALERT "spi_alloc_device() failed\n");
21         return -1;
22     }
23 
24     /* specify a chip select line */
25     spi_device->chip_select = SPI_BUS_CS1;
26 
27     /* Check whether this SPI bus.cs is already claimed */
28     snprintf(buff, sizeof(buff), "%s.%u", 
29             dev_name(&spi_device->master->dev),
30             spi_device->chip_select);
31 
32     pdev = bus_find_device_by_name(spi_device->dev.bus, NULL, buff);
33      if (pdev) {
34         /* We are not going to use this spi_device, so free it */ 
35         spi_dev_put(spi_device);
36 
37         /* 
38          * There is already a device configured for this bus.cs combination.
39          * It's okay if it's us. This happens if we previously loaded then 
40                  * unloaded our driver. 
41                  * If it is not us, we complain and fail.
42          */
43         if (pdev->driver && pdev->driver->name && 
44                 strcmp(this_driver_name, pdev->driver->name)) {
45             printk(KERN_ALERT 
46                 "Driver [%s] already registered for %s\n",
47                 pdev->driver->name, buff);
48             status = -1;
49         } 
50     } else {
51         spi_device->max_speed_hz = SPI_BUS_SPEED;
52         spi_device->mode = SPI_MODE_0;
53         spi_device->bits_per_word = 8;
54         spi_device->irq = -1;
55         spi_device->controller_state = NULL;
56         spi_device->controller_data = NULL;
57         strlcpy(spi_device->modalias, this_driver_name, SPI_NAME_SIZE);
58         status = spi_add_device(spi_device);
59 
60         if (status < 0) {    
61             spi_dev_put(spi_device);
62             printk(KERN_ALERT "spi_add_device() failed: %d\n", 
63                 status);        
64         }                
65     }
66 
67     put_device(&spi_master->dev);
68 
69     return status;
70 }

稍微有点复杂,这是个完整的样板.你完全可以只更改spi_device中指定域来服务你自己的驱动.

注册spi_driver,首先要用驱动名字还有些回调函数来初始化他.至少你得提供一个probe()函数,让他能够找到他的另一半spi_device.

范例:

1 static struct spi_driver spike_driver = {
2     .driver = {
3         .name =this_driver_name,
4         .owner =THIS_MODULE,
5     },
6     .probe =spike_probe,
7     .remove =spike_remove,
8 };

具体的也可参考linux/spi/spi.h文件

接着就可一在某个地方调用spi_register_driver()进行注册了.

1 spi_register_driver(&spike_driver);

本文转自:http://blog.csdn.net/wuhzossibility/article/details/7831652

posted on 2013-07-01 10:55 冷烟花阅读(3224) 评论(0) 编辑收藏举报