linu spi子系统驱动开发笔记之实例（2）

转载：http://blog.chinaunix.net/uid-27041925-id-3576276.html

Linux SPI子系统驱动开发

一、概述

本主题分为两个部分：

第一部分介绍基于SPI子系统开发的理论框架；

第二部分以华清远见教学平台FS_S5PC100上的M25P10芯片为例（内核版本2.6.29），编写一个SPI驱动程序实例。

二、SPI总线协议简介

介绍驱动开发前，需要先熟悉下SPI通讯协议中的几个关键的地方，后面在编写驱动时，需要考虑相关因素。

SPI总线由MISO（串行数据输入）、MOSI（串行数据输出）、SCK（串行移位时钟）、CS（使能信号）4个信号线组成。如FS_S5PC100上的M25P10芯片接线为：

 

上图中M25P10的D脚为它的数据输入脚，Q为数据输出脚，C为时钟脚。

SPI常用四种数据传输模式，主要差别在于：输出串行同步时钟极性（CPOL）和相位（CPHA）可以进行配置。

如果CPOL= 0，串行同步时钟的空闲状态为低电平；

如果CPOL= 1，串行同步时钟的空闲状态为高电平。

如果CPHA= 0，在串行同步时钟的前沿（上升或下降）数据被采样；

如果CPHA = 1，在串行同步时钟的后沿（上升或下降）数据被采样。

 

 

这四种模式的选择哪种模式取决于设备。如M25P10的手册中明确它可以支持的两种模式为：CPOL=0 CPHA=0  和 CPOL=1 CPHA=1

 

三、linux下SPI驱动开发

首先明确SPI驱动层次，如下图：       

 

以上面的图为思路：

1、 Platform bus

Platform bus对应的结构是platform_bus_type，这个内核开始就定义好的。我们不需要定义。

2、Platform_device

SPI控制器对应platform_device的定义方式，同样以S5PC100中的SPI控制器为例，参看arch/arm/plat-s5pc1xx/dev-spi.c文件

struct platform_device s3c_device_spi0 = {                          .name = "s3c64xx-spi", //名称，要和Platform_driver匹配                .id = 0, //第0个控制器，S5PC100中有3个控制器                .num_resources = ARRAY_SIZE(s5pc1xx_spi0_resource), //占用资源的种类                .resource = s5pc1xx_spi0_resource, //指向资源结构数组的指针                .dev = {                                  .dma_mask = &spi_dmamask, //dma寻址范围                         .coherent_dma_mask = DMA_BIT_MASK(32), //可以通过关闭cache等措施保证一致性的dma寻址范围                        .platform_data = &s5pc1xx_spi0_pdata, //特殊的平台数据，参看后文                },                };static struct s3c64xx_spi_cntrlr_info s5pc1xx_spi0_pdata = {                  .cfg_gpio = s5pc1xx_spi_cfg_gpio, //用于控制器管脚的IO配置        .fifo_lvl_mask = 0x7f,                  .rx_lvl_offset = 13,                };static int s5pc1xx_spi_cfg_gpio(struct platform_device *pdev)                  {                  switch (pdev->id) {                  case 0:                          s3c_gpio_cfgpin(S5PC1XX_GPB(0), S5PC1XX_GPB0_SPI_MISO0);                          s3c_gpio_cfgpin(S5PC1XX_GPB(1), S5PC1XX_GPB1_SPI_CLK0);                          s3c_gpio_cfgpin(S5PC1XX_GPB(2), S5PC1XX_GPB2_SPI_MOSI0);                          s3c_gpio_setpull(S5PC1XX_GPB(0), S3C_GPIO_PULL_UP);                          s3c_gpio_setpull(S5PC1XX_GPB(1), S3C_GPIO_PULL_UP);                          s3c_gpio_setpull(S5PC1XX_GPB(2), S3C_GPIO_PULL_UP);                        break;                  case 1:                          s3c_gpio_cfgpin(S5PC1XX_GPB(4), S5PC1XX_GPB4_SPI_MISO1);                          s3c_gpio_cfgpin(S5PC1XX_GPB(5), S5PC1XX_GPB5_SPI_CLK1);                          s3c_gpio_cfgpin(S5PC1XX_GPB(6), S5PC1XX_GPB6_SPI_MOSI1);                          s3c_gpio_setpull(S5PC1XX_GPB(4), S3C_GPIO_PULL_UP);                          s3c_gpio_setpull(S5PC1XX_GPB(5), S3C_GPIO_PULL_UP);                          s3c_gpio_setpull(S5PC1XX_GPB(6), S3C_GPIO_PULL_UP);                        break;                        case 2:                          s3c_gpio_cfgpin(S5PC1XX_GPG3(0), S5PC1XX_GPG3_0_SPI_CLK2);                          s3c_gpio_cfgpin(S5PC1XX_GPG3(2), S5PC1XX_GPG3_2_SPI_MISO2);                          s3c_gpio_cfgpin(S5PC1XX_GPG3(3), S5PC1XX_GPG3_3_SPI_MOSI2);                          s3c_gpio_setpull(S5PC1XX_GPG3(0), S3C_GPIO_PULL_UP);                          s3c_gpio_setpull(S5PC1XX_GPG3(2), S3C_GPIO_PULL_UP);                          s3c_gpio_setpull(S5PC1XX_GPG3(3), S3C_GPIO_PULL_UP);                        break;                        default:                          dev_err(&pdev->dev, "Invalid SPI Controller number!");                          return -EINVAL;                  }

3、Platform_driver

再看platform_driver，参看drivers/spi/spi_s3c64xx.c文件

static struct platform_driver s3c64xx_spi_driver = {                          .driver = {                              .name = "s3c64xx-spi", //名称，和platform_device对应                              .owner = THIS_MODULE,                          },                          .remove = s3c64xx_spi_remove,                          .suspend = s3c64xx_spi_suspend,                          .resume = s3c64xx_spi_resume,                };platform_driver_probe(&s3c64xx_spi_driver, s3c64xx_spi_probe)；//注册s3c64xx_spi_driver

和平台中注册的platform_device匹配后，调用s3c64xx_spi_probe。然后根据传入的platform_device参数，构建一个用于描述SPI控制器的结构体spi_master，并注册。spi_register_master(master)。后续注册的spi_device需要选定自己的spi_master，并利用spi_master提供的传输功能传输spi数据。

和I2C类似，SPI也有一个描述控制器的对象叫spi_master。其主要成员是主机控制器的序号（系统中可能存在多个SPI主机控制器）、片选数量、SPI模式和时钟设置用到的函数、数据传输用到的函数等。

struct spi_master 

        {                struct device dev;                s16 bus_num; //表示是SPI主机控制器的编号。由平台代码决定                u16 num_chipselect; //控制器支持的片选数量，即能支持多少个spi设备                int (*setup)(struct spi_device *spi); //针对设备设置SPI的工作时钟及数据传输模式等。在spi_add_device函数中调用。                int (*transfer)(struct spi_device *spi,                struct spi_message *mesg); //实现数据的双向传输，可能会睡眠                void (*cleanup)(struct spi_device *spi); //注销时调用        };

4、Spi bus

Spi总线对应的总线类型为spi_bus_type，在内核的drivers/spi/spi.c中定义

struct bus_type spi_bus_type = {                          .name = "spi",                          .dev_attrs = spi_dev_attrs,                          .match = spi_match_device,                          .uevent = spi_uevent,                          .suspend = spi_suspend,                          .resume = spi_resume,                };

对应的匹配规则是（高版本中的匹配规则会稍有变化，引入了id_table，可以匹配多个spi设备名称）：

static int spi_match_device(struct device *dev, struct device_driver *drv)                {                          const struct spi_device *spi = to_spi_device(dev);                          return strcmp(spi->modalias, drv->name) == 0;                }

5、spi_device

下面该讲到spi_device的构建与注册了。spi_device对应的含义是挂接在spi总线上的一个设备，所以描述它的时候应该明确它自身的设备特性、传输要求、及挂接在哪个总线上。

static struct spi_board_info s3c_spi_devs[] __initdata = {                          {                                  .modalias = "m25p10",                                   .mode = SPI_MODE_0, //CPOL=0, CPHA=0 此处选择具体数据传输模式                        .max_speed_hz = 10000000, //最大的spi时钟频率                        /* Connected to SPI-0 as 1st Slave */                                  .bus_num = 0, //设备连接在spi控制器0上                        .chip_select = 0, //片选线号，在S5PC100的控制器驱动中没有使用它作为片选的依据，而是选择了下文controller_data里的方法。                        .controller_data = &smdk_spi0_csi[0],                          },                  };                  static struct s3c64xx_spi_csinfo smdk_spi0_csi[] = {                          [0] = {                                  .set_level = smdk_m25p10_cs_set_level,                                  .fb_delay = 0x3,                          },                  };                  static void smdk_m25p10_cs_set_level(int high) //spi控制器会用这个方法设置cs                  {                          u32 val;                          val = readl(S5PC1XX_GPBDAT);                          if (high)                                  val |= (1<<3);                          else                                  val &= ~(1<<3);                          writel(val, S5PC1XX_GPBDAT);                  }spi_register_board_info(s3c_spi_devs, ARRAY_SIZE(s3c_spi_devs));//注册spi_board_info。这个代码会把spi_board_info注册要链表board_list上。

事实上上文提到的spi_master的注册会在spi_register_board_info之后，spi_master注册的过程中会调用scan_boardinfo扫描board_list，找到挂接在它上面的spi设备，然后创建并注册spi_device。

static void scan_boardinfo(struct spi_master *master)                  {                          struct boardinfo *bi;                          mutex_lock(&board_lock);                          list_for_each_entry(bi, &board_list, list) {                                  struct spi_board_info *chip = bi->board_info;                                  unsigned n;                                  for (n = bi->n_board_info; n > 0; n--, chip++) {                                          if (chip->bus_num != master->bus_num)                                          continue;                                          /* NOTE: this relies on spi_new_device to                                          * issue diagnostics when given bogus inputs                                          */                                          (void) spi_new_device(master, chip); //创建并注册了spi_device                                  }                          }                          mutex_unlock(&board_lock);                }

6、spi_driver

本文先以linux内核中的/driver/mtd/devices/m25p80.c驱动为参考。

static struct spi_driver m25p80_driver = { //spi_driver的构建                .driver = {                                  .name = "m25p80",                                  .bus = &spi_bus_type,                                  .owner = THIS_MODULE,                          },                          .probe = m25p_probe,                          .remove = __devexit_p(m25p_remove),                          */                };spi_register_driver(&m25p80_driver);//spi driver的注册在有匹配的spi device时，会调用m25p_probestatic int __devinit m25p_probe(struct spi_device *spi)        {                  ……        }

根据传入的spi_device参数，可以找到对应的spi_master。接下来就可以利用spi子系统为我们完成数据交互了。可以参看m25p80_read函数。要完成传输，先理解下面几个结构的含义：（这两个结构的定义及详细注释参见include/linux/spi/spi.h）

spi_message：描述一次完整的传输，即cs信号从高->底->高的传输
        spi_transfer：多个spi_transfer够成一个spi_message
                举例说明：m25p80的读过程如下图

 

可以分解为两个spi_ transfer一个是写命令，另一个是读数据。具体实现参见m25p80.c中的m25p80_read函数。下面内容摘取之此函数。

struct spi_transfer t[2]; //定义了两个spi_transferstruct spi_message m; //定义了两个spi_messagespi_message_init(&m); //初始化其transfers链表t[0].tx_buf = flash->command;t[0].len = CMD_SIZE + FAST_READ_DUMMY_BYTE; //定义第一个transfer的写指针和长度spi_message_add_tail(&t[0], &m); //添加到spi_messaget[1].rx_buf = buf;t[1].len = len; //定义第二个transfer的读指针和长度spi_message_add_tail(&t[1], &m); //添加到spi_messageflash->command[0] = OPCODE_READ;flash->command[1] = from >> 16;flash->command[2] = from >> 8;flash->command[3] = from; //初始化前面写buf的内容spi_sync(flash->spi, &m); //调用spi_master发送spi_message// spi_sync为同步方式发送，还可以用spi_async异步方式，那样的话，需要设置回调完成函数。另外你也可以选择一些封装好的更容易使用的函数，这些函数可以在include/linux/spi/spi.h文件中找到，如：extern int spi_write_then_read(struct spi_device *spi,                          const u8 *txbuf, unsigned n_tx,                          u8 *rxbuf, unsigned n_rx);

分析就到这里，下篇给出一个针对m25p10完整的驱动程序。


Linux下spi驱动开发之m25p10驱动测试

目标：在华清远见的FS_S5PC100平台上编写一个简单的spi驱动模块，在probe阶段实现对m25p10的ID号探测、flash擦除、flash状态读取、flash写入、flash读取等操作。代码已经经过测试，运行于2.6.35内核。理解下面代码需要参照m25p10的芯片手册。其实下面的代码和处理器没有太大关系，这也是spi子系统的分层特点。

#include <linux/platform_device.h>         #include <linux/spi/spi.h>         #include <linux/init.h>        #include <linux/module.h>        #include <linux/device.h>        #include <linux/interrupt.h>        #include <linux/mutex.h>        #include <linux/slab.h> // kzalloc        #include <linux/delay.h>#define FLASH_PAGE_SIZE 256/* Flash Operating Commands */        #define CMD_READ_ID 0x9f        #define CMD_WRITE_ENABLE 0x06         #define CMD_BULK_ERASE 0xc7        #define CMD_READ_BYTES 0x03        #define CMD_PAGE_PROGRAM 0x02        #define CMD_RDSR 0x05 /* Status Register bits. */        #define SR_WIP 1 /* Write in progress */        #define SR_WEL 2 /* Write enable latch *//* ID Numbers */        #define MANUFACTURER_ID 0x20        #define DEVICE_ID 0x1120/* Define max times to check status register before we give up. */        #define MAX_READY_WAIT_COUNT 100000        #define CMD_SZ 4struct m25p10a {                struct spi_device *spi;                struct mutex lock;                char erase_opcode;                char cmd[ CMD_SZ ];        };/*        * Internal Helper functions         *//*        * Read the status register, returning its value in the location        * Return the status register value.        * Returns negative if error occurred.        */        static int read_sr(struct m25p10a *flash)        {                ssize_t retval;                u8 code = CMD_RDSR;                u8 val;        retval = spi_write_then_read(flash->spi, &code, 1, &val, 1);        if (retval < 0) {                       dev_err(&flash->spi->dev, "error %d reading SR\n", (int) retval);                       return retval;                 }        return val;        }/*        * Service routine to read status register until ready, or timeout occurs.        * Returns non-zero if error.        */        static int wait_till_ready(struct m25p10a *flash)        {                int count;                int sr;        /* one chip guarantees max 5 msec wait here after page writes,                * but potentially three seconds (!) after page erase.                */                for (count = 0; count < MAX_READY_WAIT_COUNT; count++) {                        if ((sr = read_sr(flash)) < 0)                                break;                        else if (!(sr & SR_WIP))                                return 0;                /* REVISIT sometimes sleeping would be best */                }                  printk( "in (%s): count = %d\n", count );        return 1;        }/*        * Set write enable latch with Write Enable command.        * Returns negative if error occurred.        */        static inline int write_enable( struct m25p10a *flash )        {                flash->cmd[0] = CMD_WRITE_ENABLE;                return spi_write( flash->spi, flash->cmd, 1 );        }/*        * Erase the whole flash memory        *        * Returns 0 if successful, non-zero otherwise.        */        static int erase_chip( struct m25p10a *flash )        {                /* Wait until finished previous write command. */                if (wait_till_ready(flash))                        return -1;        /* Send write enable, then erase commands. */                write_enable( flash );                flash->cmd[0] = CMD_BULK_ERASE;                return spi_write( flash->spi, flash->cmd, 1 );        }/*        * Read an address range from the flash chip. The address range        * may be any size provided it is within the physical boundaries.        */        static int m25p10a_read( struct m25p10a *flash, loff_t from, size_t len, char *buf )        {                int r_count = 0, i;        flash->cmd[0] = CMD_READ_BYTES;                flash->cmd[1] = from >> 16;                flash->cmd[2] = from >> 8;                flash->cmd[3] = from;            #if 1                struct spi_transfer st[2];                struct spi_message msg;                    spi_message_init( &msg );                memset( st, 0, sizeof(st) );        flash->cmd[0] = CMD_READ_BYTES;                flash->cmd[1] = from >> 16;                flash->cmd[2] = from >> 8;                flash->cmd[3] = from;        st[ 0 ].tx_buf = flash->cmd;                st[ 0 ].len = CMD_SZ;                spi_message_add_tail( &st[0], &msg );        st[ 1 ].rx_buf = buf;                st[ 1 ].len = len;                spi_message_add_tail( &st[1], &msg );        mutex_lock( &flash->lock );                    /* Wait until finished previous write command. */                if (wait_till_ready(flash)) {                        mutex_unlock( &flash->lock );                        return -1;                }        spi_sync( flash->spi, &msg );                r_count = msg.actual_length - CMD_SZ;                printk( "in (%s): read %d bytes\n", __func__, r_count );                for( i = 0; i < r_count; i++ ) {                        printk( "0x%02x\n", buf[ i ] );                }        mutex_unlock( &flash->lock );        #endif        return 0;        }/*        * Write an address range to the flash chip. Data must be written in        * FLASH_PAGE_SIZE chunks. The address range may be any size provided        * it is within the physical boundaries.        */        static int m25p10a_write( struct m25p10a *flash, loff_t to, size_t len, const char *buf )        {                int w_count = 0, i, page_offset;                struct spi_transfer st[2];                struct spi_message msg;        #if 1                if (wait_till_ready(flash)) { //读状态，等待ready                mutex_unlock( &flash->lock );                return -1;                }        #endif                write_enable( flash ); //写使能                     spi_message_init( &msg );                memset( st, 0, sizeof(st) );        flash->cmd[0] = CMD_PAGE_PROGRAM;                flash->cmd[1] = to >> 16;                flash->cmd[2] = to >> 8;                flash->cmd[3] = to;        st[ 0 ].tx_buf = flash->cmd;                st[ 0 ].len = CMD_SZ;                spi_message_add_tail( &st[0], &msg );        st[ 1 ].tx_buf = buf;                st[ 1 ].len = len;                spi_message_add_tail( &st[1], &msg );        mutex_lock( &flash->lock );        /* get offset address inside a page */                page_offset = to % FLASH_PAGE_SIZE;         /* do all the bytes fit onto one page? */                if( page_offset + len <= FLASH_PAGE_SIZE ) { // yes                        st[ 1 ].len = len;                         printk("%d, cmd = %d\n", st[ 1 ].len, *(char *)st[0].tx_buf);                        //while(1)                        {                        spi_sync( flash->spi, &msg );                        }                        w_count = msg.actual_length - CMD_SZ;                }                else { // no                }                printk( "in (%s): write %d bytes to flash in total\n", __func__, w_count );                mutex_unlock( &flash->lock );                return 0;        }static int check_id( struct m25p10a *flash )         {                 char buf[10] = {0};                 flash->cmd[0] = CMD_READ_ID;                spi_write_then_read( flash->spi, flash->cmd, 1, buf, 3 );                 printk( "Manufacture ID: 0x%x\n", buf[0] );                printk( "Device ID: 0x%x\n", buf[1] | buf[2] << 8 );                return buf[2] << 16 | buf[1] << 8 | buf[0];         }static int m25p10a_probe(struct spi_device *spi)         {                 int ret = 0;                struct m25p10a *flash;                char buf[ 256 ];                printk( "%s was called\n", __func__ );                flash = kzalloc( sizeof(struct m25p10a), GFP_KERNEL );                if( !flash ) {                        return -ENOMEM;                }                flash->spi = spi;                mutex_init( &flash->lock );                /* save flash as driver's private data */                spi_set_drvdata( spi, flash );                    check_id( flash ); //读取ID        #if 1                ret = erase_chip( flash ); //擦除                 if( ret < 0 ) {                        printk( "erase the entirely chip failed\n" );                }                printk( "erase the whole chip done\n" );                memset( buf, 0x7, 256 );                m25p10a_write( flash, 0, 20, buf); //0地址写入20个7                memset( buf, 0, 256 );                m25p10a_read( flash, 0, 25, buf ); //0地址读出25个数         #endif                return 0;         }static int m25p10a_remove(struct spi_device *spi)         {                 return 0;         }static struct spi_driver m25p10a_driver = {                 .probe = m25p10a_probe,                 .remove = m25p10a_remove,                 .driver = {                         .name = "m25p10a",                 },         };static int __init m25p10a_init(void)         {                 return spi_register_driver(&m25p10a_driver);         }static void __exit m25p10a_exit(void)         {                 spi_unregister_driver(&m25p10a_driver);         }module_init(m25p10a_init);         module_exit(m25p10a_exit);MODULE_DESCRIPTION("m25p10a driver for FS_S5PC100");MODULE_LICENSE("GPL");