Linux下spi驱动开发

作者：刘洪涛,讲师。

一、概述

基于子系统去开发驱动程序已经是linux内核中普遍的做法了。前面写过基于I2C子系统的驱动开发。本文介绍另外一种常用总线SPI的开发方法。SPI子系统的开发和I2C有很多的相似性，大家可以对比学习。本主题分为两个部分叙述，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。

 

 

这四种模式中究竟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：       

 

我们以上面的这个图为思路

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_probe

static 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_transfer
                  struct spi_message m; //定义了两个spi_message
                spi_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_message
                  t[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_message
                  flash->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);

这篇博文就到这了，下篇给出一个针对m25p10完整的驱动程序。 


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 4

struct 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");