Linux驱动开发（十九）：SPI驱动

简介

SPI同样使我们在单片机开发中较为常用的通信接口，常用于诸如FLASH、OLED、SD卡的流式数据的读写，全双工总线，具体的关于协议的知识这里就不说了，我们主要讨论Linux的SPI设备驱动框架以及我们如何去编写一个SPI设备驱动
Linux下的SPI驱动和I2C驱动类似，也是分为主机控制器驱动和设备驱动

驱动框架介绍

SPI主机驱动

SOC的SPI控制器驱动，Linux内核使用spi_master表示SPI主机驱动
spi_master结构体定义在\linux\spi\spi.h
这是一个庞大的结构体定义，封装了很多操作函数以、私有标志以及锁等元素
其中有两个比较重要的函数

int (*transfer)(struct spi_device *spi,struct spi_message *mesg);
int (*transfer_one_message)(struct spi_master *master,struct spi_message *mesg);

transfer函数和i2c_algorithm中的master_xfer函数一样，是控制器的数据传输函数
transfer_one_message函数也用于SPI数据发送，用于发送一个spi_message,SPI的数据通常会打包成一个spi_message然后用队列方式发送出去
对于SPI主机驱动来说主要就是实现transfer函数，以此来实现与设备的通信
与I2C主机驱动一样，SPI主机驱动一般由SOC厂商编写
SPI主机驱动的核心就是申请spi_master，然后初始化spi_master，最后向Linux内核注册

spi_master的申请与释放

• 申请：
  struct spi_master *spi_alloc_master(struct device *dev, unsigned size)
  dev：设备，一般是platform_device中的dev成员变量
  size：私有数据大小，可以通过spi_master_get_devdata函数获取这些私有数据
• 释放：
  static inline void spi_master_put(struct spi_master *master)

spi_master的注册与注销

• 注册：
  int spi_register_master(struct spi_master *master);
• 注销：
  void spi_unregister_master(struct spi_master *master);

SPI设备驱动

与I2C设备驱动很类似，使用spi_driver结构体来表示SPI设备驱动

struct spi_driver {
	const struct spi_device_id *id_table;
	int			(*probe)(struct spi_device *spi);
	int			(*remove)(struct spi_device *spi);
	void			(*shutdown)(struct spi_device *spi);
	struct device_driver	driver;
};

与i2c_driver、platform_driver基本一样，设备和驱动匹配以后会执行probe函数

spi_driver注册与注销

• 注册：
  int spi_register_driver(struct spi_driver *sdrv);
• 注销：
  void spi_unregister_driver(struct spi_driver *sdrv)

SPI驱动和设备的匹配过程

SPI的总线为spi_bus_type，定义在\drivers\spi\spi.c

struct bus_type spi_bus_type = {
	.name		= "spi",
	.dev_groups	= spi_dev_groups,
	.match		= spi_match_device,
	.uevent		= spi_uevent,
};

可以看出匹配函数为spi_match_device

static int spi_match_device(struct device *dev, struct device_driver *drv)
{
	const struct spi_device	*spi = to_spi_device(dev);
	const struct spi_driver	*sdrv = to_spi_driver(drv);

	/* Attempt an OF style match */
	if (of_driver_match_device(dev, drv))
		return 1;

	/* Then try ACPI */
	if (acpi_driver_match_device(dev, drv))
		return 1;

	if (sdrv->id_table)
		return !!spi_match_id(sdrv->id_table, spi);

	return strcmp(spi->modalias, drv->name) == 0;
}

可以使用设备树、ACPI和通过对比id_table匹配，在我们使用设备树时一般都是使用设备树来匹配的

主机驱动分析

一般由SOC厂商编写
imx6ull.dsi文件中

ecspi3: ecspi@02010000 {
	#address-cells = <1>;
	#size-cells = <0>;
	compatible = "fsl,imx6ul-ecspi", "fsl,imx51-ecspi";
	reg = <0x02010000 0x4000>;
	interrupts = <GIC_SPI 33 IRQ_TYPE_LEVEL_HIGH>;
	clocks = <&clks IMX6UL_CLK_ECSPI3>,
		 <&clks IMX6UL_CLK_ECSPI3>;
	clock-names = "ipg", "per";
	dmas = <&sdma 7 7 1>, <&sdma 8 7 2>;
	dma-names = "rx", "tx";
	status = "disabled";
};

compatible有两个属性值"fsl,imx6ul-ecspi", “fsl,imx51-ecspi”，使用这两个属性值来查找主机驱动
主机驱动实现在\drivers\spi\spi-imx.c

static struct platform_device_id spi_imx_devtype[] = {
	{
		.name = "imx1-cspi",
		.driver_data = (kernel_ulong_t) &imx1_cspi_devtype_data,
	}, {
		.name = "imx21-cspi",
		.driver_data = (kernel_ulong_t) &imx21_cspi_devtype_data,
	}, {
		.name = "imx27-cspi",
		.driver_data = (kernel_ulong_t) &imx27_cspi_devtype_data,
	}, {
		.name = "imx31-cspi",
		.driver_data = (kernel_ulong_t) &imx31_cspi_devtype_data,
	}, {
		.name = "imx35-cspi",
		.driver_data = (kernel_ulong_t) &imx35_cspi_devtype_data,
	}, {
		.name = "imx51-ecspi",
		.driver_data = (kernel_ulong_t) &imx51_ecspi_devtype_data,
	}, {
		.name = "imx6ul-ecspi",
		.driver_data = (kernel_ulong_t) &imx6ul_ecspi_devtype_data,
	}, {
		/* sentinel */
	}
};

static const struct of_device_id spi_imx_dt_ids[] = {
	{ .compatible = "fsl,imx1-cspi", .data = &imx1_cspi_devtype_data, },
	{ .compatible = "fsl,imx21-cspi", .data = &imx21_cspi_devtype_data, },
	{ .compatible = "fsl,imx27-cspi", .data = &imx27_cspi_devtype_data, },
	{ .compatible = "fsl,imx31-cspi", .data = &imx31_cspi_devtype_data, },
	{ .compatible = "fsl,imx35-cspi", .data = &imx35_cspi_devtype_data, },
	{ .compatible = "fsl,imx51-ecspi", .data = &imx51_ecspi_devtype_data, },
	{ .compatible = "fsl,imx6ul-ecspi", .data = &imx6ul_ecspi_devtype_data, },
	{ /* sentinel */ }
};

上面的为SPI无设备树匹配表
下面的是设备树匹配表
我们看一下platform_driver驱动框架，SPI主机驱动使用了platform驱动框架

static struct platform_driver spi_imx_driver = {
	.driver = {
		   .name = DRIVER_NAME,
		   .of_match_table = spi_imx_dt_ids,
		   .pm = IMX_SPI_PM,
	},
	.id_table = spi_imx_devtype,
	.probe = spi_imx_probe,
	.remove = spi_imx_remove,
};

spi_imx_probe函数会从设备树中读取相应的节点属性值，申请并初始化spi_master，最后调用spi_bitbang_start函数（spi_bitbang_start会调用spi_register_master函数）向linux内核注册spi_master
对于I.MX6U来讲，SPI主机的最终收发函数为spi_imx_transfer，此函数通过如下层层调用实现SPI数据发送

spi_imx_transfer
		-> spi_imx_pio_transfer
			-> spi_imx_push
				-> spi_imx->tx

tx和rx这两个变量分别为SPI的数据发送和接收函数，而tx和rx这两个变量是结构体spi_imx_data 的成员
结构体 spi_imx_data定义如下

struct spi_imx_data {
	struct spi_bitbang bitbang;

	struct completion xfer_done;
	void __iomem *base;
	struct clk *clk_per;
	struct clk *clk_ipg;
	unsigned long spi_clk;

	unsigned int count;
	void (*tx)(struct spi_imx_data *);
	void (*rx)(struct spi_imx_data *);
	void *rx_buf;
	const void *tx_buf;
	unsigned int txfifo; /* number of words pushed in tx FIFO */

	/* DMA */
	unsigned int dma_is_inited;
	unsigned int dma_finished;
	bool usedma;
	u32 rx_wml;
	u32 tx_wml;
	u32 rxt_wml;
	struct completion dma_rx_completion;
	struct completion dma_tx_completion;
	struct dma_slave_config rx_config;
	struct dma_slave_config tx_config;

	const struct spi_imx_devtype_data *devtype_data;
	int chipselect[0];
};

I.MX6U SPI主机驱动会维护一个 spi_imx_data类型的变量 spi_imx，并且使用 spi_imx_setupxfer函数来设置 spi_imx的 tx和 rx函数。
可以收发8、16、32位的数据

spi_imx_buf_tx_u8 
spi_imx_buf_tx_u16 
spi_imx_buf_tx_u32
spi_imx_buf_rx_u8 
spi_imx_buf_rx_u16 
spi_imx_buf_rx_u32

这六个函数是通过如下的方式创建的

#define MXC_SPI_BUF_RX(type)						\
static void spi_imx_buf_rx_##type(struct spi_imx_data *spi_imx)		\
{									\
	unsigned int val = readl(spi_imx->base + MXC_CSPIRXDATA);	\
									\
	if (spi_imx->rx_buf) {						\
		*(type *)spi_imx->rx_buf = val;				\
		spi_imx->rx_buf += sizeof(type);			\
	}								\
}

#define MXC_SPI_BUF_TX(type)						\
static void spi_imx_buf_tx_##type(struct spi_imx_data *spi_imx)		\
{									\
	type val = 0;							\
									\
	if (spi_imx->tx_buf) {						\
		val = *(type *)spi_imx->tx_buf;				\
		spi_imx->tx_buf += sizeof(type);			\
	}								\
									\
	spi_imx->count -= sizeof(type);					\
									\
	writel(val, spi_imx->base + MXC_CSPITXDATA);			\
}

MXC_SPI_BUF_RX(u8)
MXC_SPI_BUF_TX(u8)
MXC_SPI_BUF_RX(u16)
MXC_SPI_BUF_TX(u16)
MXC_SPI_BUF_RX(u32)
MXC_SPI_BUF_TX(u32)

通过使用‘##’拼接符的方式巧妙的创建了六个函数

SPI设备驱动编写流程

SPI设备描述

pinctrl子节点的创建与修改

根据使用的IO来创建或者修改pinctrl节点，要注意检查相应的IO有没有被其他的设备所使用，如果有的话要将其删除
例子：

pinctrl_ecspi3: ecspi3grp {
        fsl,pins = <
                MX6UL_PAD_UART2_RTS_B__ECSPI3_MISO        0x100b1  /* MISO*/
                MX6UL_PAD_UART2_CTS_B__ECSPI3_MOSI        0x100b1  /* MOSI*/
                MX6UL_PAD_UART2_RX_DATA__ECSPI3_SCLK      0x100b1  /* CLK*/
                MX6UL_PAD_UART2_TX_DATA__GPIO1_IO20       0x100b0  /* CS*/
        >;
};

这里很容易理解，就是对引脚的复用和IO配置

SPI设备节点的创建和修改

例子：

&ecspi1 {
	fsl,spi-num-chipselects = <1>;
	cs-gpios = <&gpio4 9 0>;
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_ecspi1>;
	status = "okay";

	flash: m25p80@0 {
		#address-cells = <1>;
		#size-cells = <1>;
		compatible = "st,m25p32";
		spi-max-frequency = <20000000>;
		reg = <0>;
	};
};

fsl,spi-num-chipselects 属性为1，表示只有一个设备
cs-gpios 表示片选信号为gpio4_IO09
pinctrl-names就是SPI设备使用的IO名字
pinctrl-0 所使用的IO对应的pinctrl节点
status 设置为okay
m25p80@0 设备为m25p80，0表示m25p80接到了ECSPI的通道0上
compatible SPI设备用于匹配驱动的标识
spi-max-frequency 设置SPI控制器的最高频率，要根据所使用的SPI设备来设置，这里设置为了20MHZ
reg 表示使用ECSPI的通道0
我们编写ICM20608的设备树节点信息的时候就参考这个内容

SPI设备数据收发流程

SPI设备驱动的核心是spi_driver
在内核注册成功spi_driver后就可以使用SPI核心层提供的API函数来对设备进行读写操作了
首先是spi_transfer结构体，此结构体用于描述SPI传输信息

struct spi_transfer {
	/* it's ok if tx_buf == rx_buf (right?)
	 * for MicroWire, one buffer must be null
	 * buffers must work with dma_*map_single() calls, unless
	 *   spi_message.is_dma_mapped reports a pre-existing mapping
	 */
	const void	*tx_buf;
	void		*rx_buf;
	unsigned	len;

	dma_addr_t	tx_dma;
	dma_addr_t	rx_dma;
	struct sg_table tx_sg;
	struct sg_table rx_sg;

	unsigned	cs_change:1;
	unsigned	tx_nbits:3;
	unsigned	rx_nbits:3;
#define	SPI_NBITS_SINGLE	0x01 /* 1bit transfer */
#define	SPI_NBITS_DUAL		0x02 /* 2bits transfer */
#define	SPI_NBITS_QUAD		0x04 /* 4bits transfer */
	u8		bits_per_word;
	u16		delay_usecs;
	u32		speed_hz;

	struct list_head transfer_list;
};

tx_buf保存着要发送的数据
rx_buf保存接收到的数据
len是要进行传输的数据长度，SPI是全双工通信，因此在一次通信中发送和接收的字节数都是一样的，所以spi_transfer中就没有发送长度和接收长度之分

spi_transfer需要组织成spi_message，spi_message也是一个结构体

struct spi_message {
	struct list_head	transfers;

	struct spi_device	*spi;

	unsigned		is_dma_mapped:1;

	/* REVISIT:  we might want a flag affecting the behavior of the
	 * last transfer ... allowing things like "read 16 bit length L"
	 * immediately followed by "read L bytes".  Basically imposing
	 * a specific message scheduling algorithm.
	 *
	 * Some controller drivers (message-at-a-time queue processing)
	 * could provide that as their default scheduling algorithm.  But
	 * others (with multi-message pipelines) could need a flag to
	 * tell them about such special cases.
	 */

	/* completion is reported through a callback */
	void			(*complete)(void *context);
	void			*context;
	unsigned		frame_length;
	unsigned		actual_length;
	int			status;

	/* for optional use by whatever driver currently owns the
	 * spi_message ...  between calls to spi_async and then later
	 * complete(), that's the spi_master controller driver.
	 */
	struct list_head	queue;
	void			*state;
};

在使用spi_message之前需要对其进行初始化，spi_message初始化函数为spi_message_init

	void spi_message_init(struct spi_message *m)；

初始化完成后需要将spi_transfer添加到spi_message队列中，这里我们要使用

	void spi_message_add_tail(struct spi_transfer *t, struct spi_message *m)；

spi_message准备好以后就可以进行数据传输了，数据传输分为同步传输和异步传输，同步传输会阻塞的等待SPI数据传输完成，同步传输函数为 spi_sync

	int spi_sync(struct spi_device *spi, struct spi_message *message);

异步传输不会阻塞的等待SPI数据传输完成，异步传输需要设置spi_message中的complete成员变量，complete是一个回调函数，当SPI数据传输完成后此函数会被调用，SPI异步传输函数为spi_async

	int spi_async(struct spi_device *spi, struct spi_message *message);

SPI数据传输的步骤

• 1、申请并初始化 spi_transfer，设置 spi_transfer的 tx_buf成员变量， tx_buf为要发送的数据。然后设置 rx_buf成员变量， rx_buf保存着接收到的数据。最后设置 len成员变量，也就是要进行数据通信的长度。
• 2、使用 spi_message_init函数初始化 spi_message
• 3、使用 spi_message_add_tail函数将前面设置好的 spi_transfer添加到 spi_message队中。
• 4、使用 spi_sync函数完成 SPI数据同步传输。

实验程序编写

硬件介绍

我们使用的模块是正点原子开发板上板载的icm20608六轴传感器模块
可以读到的数据为温度、3轴加速度、3轴角速度数据
我们的编写的是设备驱动，所以分为修改设备树、编写驱动程序、编写应用程序三个部分

修改设备树

pinctrl

该传感器连接在SPI3上

pinctrl_ecspi3: ecspi3grp {
           fsl,pins = <
                   MX6UL_PAD_UART2_RTS_B__ECSPI3_MISO        0x100b1  /* MISO*/
                   MX6UL_PAD_UART2_CTS_B__ECSPI3_MOSI        0x100b1  /* MOSI*/
                   MX6UL_PAD_UART2_RX_DATA__ECSPI3_SCLK      0x100b1  /* CLK*/
                   MX6UL_PAD_UART2_TX_DATA__GPIO1_IO20       0x100b0  /* CS*/
           >;
   		};

ecspi3

&ecspi3 {
        fsl,spi-num-chipselects = <1>;
        cs-gpio = <&gpio1 20 GPIO_ACTIVE_LOW>;
        pinctrl-names = "default";
        pinctrl-0 = <&pinctrl_ecspi3>;
        status = "okay";

       spidev: icm20608@0 {
       compatible = "alientek,icm20608";
         spi-max-frequency = <8000000>;
         reg = <0>;
    };
};

注意：没有配置cs-gpios而是用了一个自己定义的cs-gpio（不带s），因为我们要自己控制片选引脚，如果使用cs-gpios属性点额话SPI主机驱动就会控制片选引脚
pinctrl-0引用了我们前面定义的pinctrl
spi-max-frequency为8MHZ这是因为icm20608的SPI口最大支持8M

编写驱动程序

icm20608_reg.h

这个头文件定义了一些相关的寄存器地址

#ifndef ICM20608_REG_H
#define ICM20608_REG_H

#define ICM20608G_ID			0XAF	/* ID值 */
#define ICM20608D_ID			0XAE	/* ID值 */

/* ICM20608寄存器 
 *复位后所有寄存器地址都为0，除了
 *Register 107(0X6B) Power Management 1 	= 0x40
 *Register 117(0X75) WHO_AM_I 				= 0xAF或0xAE
 */
/* 陀螺仪和加速度自测(出产时设置，用于与用户的自检输出值比较） */
#define	ICM20_SELF_TEST_X_GYRO		0x00
#define	ICM20_SELF_TEST_Y_GYRO		0x01
#define	ICM20_SELF_TEST_Z_GYRO		0x02
#define	ICM20_SELF_TEST_X_ACCEL		0x0D
#define	ICM20_SELF_TEST_Y_ACCEL		0x0E
#define	ICM20_SELF_TEST_Z_ACCEL		0x0F

/* 陀螺仪静态偏移 */
#define	ICM20_XG_OFFS_USRH			0x13
#define	ICM20_XG_OFFS_USRL			0x14
#define	ICM20_YG_OFFS_USRH			0x15
#define	ICM20_YG_OFFS_USRL			0x16
#define	ICM20_ZG_OFFS_USRH			0x17
#define	ICM20_ZG_OFFS_USRL			0x18

#define	ICM20_SMPLRT_DIV			0x19
#define	ICM20_CONFIG				0x1A
#define	ICM20_GYRO_CONFIG			0x1B
#define	ICM20_ACCEL_CONFIG			0x1C
#define	ICM20_ACCEL_CONFIG2			0x1D
#define	ICM20_LP_MODE_CFG			0x1E
#define	ICM20_ACCEL_WOM_THR			0x1F
#define	ICM20_FIFO_EN				0x23
#define	ICM20_FSYNC_INT				0x36
#define	ICM20_INT_PIN_CFG			0x37
#define	ICM20_INT_ENABLE			0x38
#define	ICM20_INT_STATUS			0x3A

/* 加速度输出 */
#define	ICM20_ACCEL_XOUT_H			0x3B
#define	ICM20_ACCEL_XOUT_L			0x3C
#define	ICM20_ACCEL_YOUT_H			0x3D
#define	ICM20_ACCEL_YOUT_L			0x3E
#define	ICM20_ACCEL_ZOUT_H			0x3F
#define	ICM20_ACCEL_ZOUT_L			0x40

/* 温度输出 */
#define	ICM20_TEMP_OUT_H			0x41
#define	ICM20_TEMP_OUT_L			0x42

/* 陀螺仪输出 */
#define	ICM20_GYRO_XOUT_H			0x43
#define	ICM20_GYRO_XOUT_L			0x44
#define	ICM20_GYRO_YOUT_H			0x45
#define	ICM20_GYRO_YOUT_L			0x46
#define	ICM20_GYRO_ZOUT_H			0x47
#define	ICM20_GYRO_ZOUT_L			0x48

#define	ICM20_SIGNAL_PATH_RESET		0x68
#define	ICM20_ACCEL_INTEL_CTRL 		0x69
#define	ICM20_USER_CTRL				0x6A
#define	ICM20_PWR_MGMT_1			0x6B
#define	ICM20_PWR_MGMT_2			0x6C
#define	ICM20_FIFO_COUNTH			0x72
#define	ICM20_FIFO_COUNTL			0x73
#define	ICM20_FIFO_R_W				0x74
#define	ICM20_WHO_AM_I 				0x75

/* 加速度静态偏移 */
#define	ICM20_XA_OFFSET_H			0x77
#define	ICM20_XA_OFFSET_L			0x78
#define	ICM20_YA_OFFSET_H			0x7A
#define	ICM20_YA_OFFSET_L			0x7B
#define	ICM20_ZA_OFFSET_H			0x7D
#define	ICM20_ZA_OFFSET_L 			0x7E


#endif

icm20608_driver.c

这个是主要的驱动文件

#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/delay.h>
#include <linux/ide.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/errno.h>
#include <linux/gpio.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/of_gpio.h>
#include <linux/semaphore.h>
#include <linux/timer.h>
#include <linux/i2c.h>
#include <linux/spi/spi.h>
#include <linux/of.h>
#include <linux/of_address.h>
#include <linux/of_gpio.h>
#include <linux/platform_device.h>
#include <asm/mach/map.h>
#include <asm/uaccess.h>
#include <asm/io.h>
//#include <linux/slab.h>
//#include <linux/gfp.h>
#include "icm20608_reg.h"

#define ICM20608_CNT 1
#define ICM20608_NAME "icm20608"

struct icm20608_dev {
    dev_t devid;
    struct cdev cdev;
    struct class *class;
    struct device *device;
    struct device_node *nd;
    int major;
    void *private_data;
    int cs_gpio;//SPI CS Pin
    signed int gyro_x_adc;
    signed int gyro_y_adc;
    signed int gyro_z_adc;
    signed int accel_x_adc;
    signed int accel_y_adc;
    signed int accel_z_adc;
    signed int temp_adc;
};

static struct icm20608_dev icm20608dev;

static int icm20608_read_regs(struct icm20608_dev *dev, u8 reg, void *buf, int len)
{
    int ret ;
    unsigned char txdata[len];
    struct spi_message m;
    struct spi_transfer *t;
    struct spi_device *spi = (struct spi_device *)dev->private_data;

    
    t = kzalloc(sizeof(struct spi_transfer), GFP_KERNEL);//alloced memory
    gpio_set_value(dev->cs_gpio, 0);

    /*first time : send reg addr to be read*/
    txdata[0] = reg | 0x80;//set reg addr bit8 to 1(write state)
    t->tx_buf = txdata;
    t->len = 1;
    spi_message_init(&m);
    spi_message_add_tail(t, &m);
    ret = spi_sync(spi, &m);

    /*second time : read data*/
    txdata[0] = 0xff;//send 0xff while read ,pointless
    t->rx_buf = buf;
    t->len = len;
    spi_message_init(&m);
    spi_message_add_tail(t, &m);
    ret = spi_sync(spi, &m);

    kfree(t);//free memory
    gpio_set_value(dev->cs_gpio, 1);
    return ret;
}

static s32 icm20608_write_regs(struct icm20608_dev *dev, u8 reg, u8 *buf, u8 len)
{
    int ret ;
    unsigned char txdata[len];
    struct spi_message m;
    struct spi_transfer *t;
    struct spi_device *spi = (struct spi_device *)dev->private_data;    

    
    t = kzalloc(sizeof(struct spi_transfer), GFP_KERNEL);//alloced memory
    gpio_set_value(dev->cs_gpio, 0);

    /*first time : send reg addr to be read */
    txdata[0] = reg & ~0x80;//set reg addr bit8 to 1(write state)
    t->tx_buf = txdata;
    t->len = 1;
    spi_message_init(&m);
    spi_message_add_tail(t, &m);
    ret = spi_sync(spi, &m);   

    /*second time : send data to write*/
    t->tx_buf = buf;
    t->len = len;
    spi_message_init(&m);
    spi_message_add_tail(t, &m);
    ret = spi_sync(spi, &m);

    kfree(t);//free memory
    gpio_set_value(dev->cs_gpio, 1);
    return ret;    
   
}

static unsigned char icm20608_read_onereg(struct icm20608_dev *dev, u8 reg)
{
    u8 data = 0;
    icm20608_read_regs(dev, reg, &data, 1);
    return data;
}

static void icm20608_write_onereg(struct icm20608_dev *dev, u8 reg, u8 value)
{
    u8 buf = value;
    icm20608_write_regs(dev, reg, &buf, 1);
}

void icm20608_readdata(struct icm20608_dev *dev)
{
    unsigned char data[14];
    icm20608_read_regs(dev, ICM20_ACCEL_XOUT_H, data, 14);

    dev->accel_x_adc = (signed short)((data[0]<<8) | data[1]);
    dev->accel_y_adc = (signed short)((data[2]<<8) | data[3]);
    dev->accel_z_adc = (signed short)((data[4]<<8) | data[5]);
    dev->temp_adc = (signed short)((data[6]<<8) | data[7]);
    dev->gyro_x_adc = (signed short)((data[8]<<8) | data[9]);
    dev->gyro_y_adc = (signed short)((data[10]<<8) | data[11]);
    dev->gyro_z_adc = (signed short)((data[12]<<8) | data[13]);
}


void icm20608_reginit(void)
{
	u8 value = 0;
	
	icm20608_write_onereg(&icm20608dev, ICM20_PWR_MGMT_1, 0x80);
	mdelay(50);
	icm20608_write_onereg(&icm20608dev, ICM20_PWR_MGMT_1, 0x01);
	mdelay(50);

	value = icm20608_read_onereg(&icm20608dev, ICM20_WHO_AM_I);
	printk("ICM20608 ID = %#X\r\n", value);	

	icm20608_write_onereg(&icm20608dev, ICM20_SMPLRT_DIV, 0x00); 	/* 输出速率是内部采样率					*/
	icm20608_write_onereg(&icm20608dev, ICM20_GYRO_CONFIG, 0x18); 	/* 陀螺仪±2000dps量程 				*/
	icm20608_write_onereg(&icm20608dev, ICM20_ACCEL_CONFIG, 0x18); 	/* 加速度计±16G量程 					*/
	icm20608_write_onereg(&icm20608dev, ICM20_CONFIG, 0x04); 		/* 陀螺仪低通滤波BW=20Hz 				*/
	icm20608_write_onereg(&icm20608dev, ICM20_ACCEL_CONFIG2, 0x04); /* 加速度计低通滤波BW=21.2Hz 			*/
	icm20608_write_onereg(&icm20608dev, ICM20_PWR_MGMT_2, 0x00); 	/* 打开加速度计和陀螺仪所有轴 				*/
	icm20608_write_onereg(&icm20608dev, ICM20_LP_MODE_CFG, 0x00); 	/* 关闭低功耗 						*/
	icm20608_write_onereg(&icm20608dev, ICM20_FIFO_EN, 0x00);		/* 关闭FIFO						*/
}


static int icm20608_open(struct inode *inode, struct file *filp)
{
    filp->private_data = &icm20608dev;
    return 0;
}

static ssize_t icm20608_read(struct file *filp, char __user *buf, size_t cnt, loff_t *off)
{
    signed int data[7];
    long err = 0;
    struct icm20608_dev *dev = (struct icm20608_dev *)filp->private_data;

    icm20608_readdata(dev);
    data[0] = dev->gyro_x_adc;
    data[1] = dev->gyro_y_adc;
    data[2] = dev->gyro_z_adc;
    data[3] = dev->accel_x_adc;
    data[4] = dev->accel_y_adc;
    data[5] = dev->accel_z_adc;
    data[6] = dev->temp_adc;

    err = copy_to_user(buf, data, sizeof(data));
    return 0;
}


static int icm20608_release(struct inode *inode, struct file *filp)
{
    return 0;
}


static const struct file_operations icm20608_ops = {
    .owner = THIS_MODULE,
    .open = icm20608_open,
    .read = icm20608_read,
    .release = icm20608_release,
};
 
static int icm20608_peobe(struct spi_device *spi)
{
    int ret = 0;
    /*1.get device id*/
    if(icm20608dev.major)
    {
        icm20608dev.devid = MKDEV(icm20608dev.major, 0);
        register_chrdev_region(icm20608dev.devid, ICM20608_CNT, ICM20608_NAME);
    }    
    else
    {
        alloc_chrdev_region(&icm20608dev.devid, 0, ICM20608_CNT, ICM20608_NAME);
        icm20608dev.major = MAJOR(icm20608dev.devid);
    }

    /*2.register device*/
    cdev_init(&icm20608dev.cdev, &icm20608_ops);
    cdev_add(&icm20608dev.cdev, icm20608dev.devid, ICM20608_CNT);
    //printk("Probe OK2!\r\n");
    /*3.create class*/
    icm20608dev.class = class_create(THIS_MODULE, ICM20608_NAME);
    if(IS_ERR(icm20608dev.class))
    {
        printk("CLASS ERROR!!\r\n");
        return PTR_ERR(icm20608dev.class);

    }
    //printk("Probe OK3!\r\n");
    /*4.create device*/
    icm20608dev.device = device_create(icm20608dev.class, NULL, icm20608dev.devid, NULL, ICM20608_NAME);
    if(IS_ERR(icm20608dev.device))
    {
        return PTR_ERR(icm20608dev.device);
    }
    //printk("Probe OK4!\r\n");
    /*5.get cs from dts*/
    //icm20608dev.nd = of_find_node_by_path("soc/aips-bus@02000000/spba-bus@02000000/ecspi@02010000");
    icm20608dev.nd = of_find_node_by_path("/soc/aips-bus@02000000/spba-bus@02000000/ecspi@02010000");
    if(icm20608dev.nd == NULL)
    {
        printk("ecspi3 node not find!\r\n");
        return -EINVAL;
    }
    //printk("Probe OK5!\r\n");
    /*6.get gpio property from dts*/
    icm20608dev.cs_gpio = of_get_named_gpio(icm20608dev.nd, "cs-gpio", 0);
    if(icm20608dev.cs_gpio <0)
    {
        printk("can't get cs-gpio!\r\n");
        return -EINVAL;
    }

    /*7.set gpio output and set high*/
    ret = gpio_direction_output(icm20608dev.cs_gpio, 1);
    if(ret < 0)
    {
        printk("can't set gpio!\r\n");
    }

    /*8.init spi_device*/
    spi->mode = SPI_MODE_0;
    spi_setup(spi);
    icm20608dev.private_data = spi;//set private_data

    /*9.init ICM20608 inside register*/
    icm20608_reginit();

    printk("Probe OK!\r\n");

    return 0;
}

static int icm20608_remove(struct spi_device *spi)
{
    /*delete device*/
    cdev_del(&icm20608dev.cdev);
    unregister_chrdev_region(icm20608dev.devid, ICM20608_CNT);

    /*unregister class and device*/
    device_destroy(icm20608dev.class, icm20608dev.devid);
    class_destroy(icm20608dev.class);
    return 0;
}

static const struct spi_device_id icm20608_id[] = {
    {"alientek,icm20608", 0},
    {}
};

static const struct of_device_id icm20608_of_match[] = {
    {.compatible = "alientek,icm20608" },
    {}
};

static struct spi_driver icm20608_driver = {
    .probe = icm20608_peobe,
    .remove = icm20608_remove,
    .driver = {
        .owner = THIS_MODULE,
        .name = "icm20608",
        .of_match_table = icm20608_of_match,
    },
    .id_table = icm20608_id,
};

static int __init icm20608_init(void)
{
    return spi_register_driver(&icm20608_driver);
}

static void __exit icm20608_exit(void)
{
    spi_unregister_driver(&icm20608_driver);
}

module_init(icm20608_init);
module_exit(icm20608_exit);
MODULE_LICENSE("GPL");
MODULE_AUTHOR("GYY");

这个代码是比较长的，接下来我们对代码进行分析

驱动代码分析

• 在icm20608_init函数中我们调用了spi_register_driver来注册了一个SPI驱动，传入了一个icm20608_driver 参数
• icm20608_driver 中定义了probe和remove函数以及设备和驱动的匹配规则，我们可以使用设备树和id_tables两种匹配方式
• 在probe函数中主要完成字符设备的注册、GPIO的获取以及初始化以及SPI设备的初始化
• 设备驱动的实现关键就是提供给应用层接口，icm20608_ops就是该设备驱动的操作函数，我们实现了icm20608_open、icm20608_read和icm20608_release函数
• icm20608_read函数中我们就实现了从模块读取温度、角速度、加速度数据，我们可以在应用层调用read函数来读取

应用层代码

#include "stdio.h"
#include "unistd.h"
#include "sys/types.h"
#include "sys/stat.h"
#include "sys/ioctl.h"
#include "fcntl.h"
#include "stdlib.h"
#include "string.h"
#include <poll.h>
#include <sys/select.h>
#include <sys/time.h>
#include <signal.h>
#include <fcntl.h>

/*
 * @description		: main主程序
 * @param - argc 	: argv数组元素个数
 * @param - argv 	: 具体参数
 * @return 			: 0 成功;其他 失败
 */
int main(int argc, char *argv[])
{
	int fd;
	char *filename;
	signed int databuf[7];
	unsigned char data[14];
	signed int gyro_x_adc, gyro_y_adc, gyro_z_adc;
	signed int accel_x_adc, accel_y_adc, accel_z_adc;
	signed int temp_adc;

	float gyro_x_act, gyro_y_act, gyro_z_act;
	float accel_x_act, accel_y_act, accel_z_act;
	float temp_act;

	int ret = 0;

	if (argc != 2) {
		printf("Error Usage!\r\n");
		return -1;
	}

	filename = argv[1];
	fd = open(filename, O_RDWR);
	if(fd < 0) {
		printf("can't open file %s\r\n", filename);
		return -1;
	}

	while (1) {
		ret = read(fd, databuf, sizeof(databuf));
		if(ret == 0) { 			/* 数据读取成功 */
			gyro_x_adc = databuf[0];
			gyro_y_adc = databuf[1];
			gyro_z_adc = databuf[2];
			accel_x_adc = databuf[3];
			accel_y_adc = databuf[4];
			accel_z_adc = databuf[5];
			temp_adc = databuf[6];

			/* 计算实际值 */
			gyro_x_act = (float)(gyro_x_adc)  / 16.4;
			gyro_y_act = (float)(gyro_y_adc)  / 16.4;
			gyro_z_act = (float)(gyro_z_adc)  / 16.4;
			accel_x_act = (float)(accel_x_adc) / 2048;
			accel_y_act = (float)(accel_y_adc) / 2048;
			accel_z_act = (float)(accel_z_adc) / 2048;
			temp_act = ((float)(temp_adc) - 25 ) / 326.8 + 25;


			printf("\r\n原始值:\r\n");
			printf("gx = %d, gy = %d, gz = %d\r\n", gyro_x_adc, gyro_y_adc, gyro_z_adc);
			printf("ax = %d, ay = %d, az = %d\r\n", accel_x_adc, accel_y_adc, accel_z_adc);
			printf("temp = %d\r\n", temp_adc);
			printf("实际值:");
			printf("act gx = %.2f°/S, act gy = %.2f°/S, act gz = %.2f°/S\r\n", gyro_x_act, gyro_y_act, gyro_z_act);
			printf("act ax = %.2fg, act ay = %.2fg, act az = %.2fg\r\n", accel_x_act, accel_y_act, accel_z_act);
			printf("act temp = %.2f°C\r\n", temp_act);
		}
		usleep(100000); /*100ms */
	}
	close(fd);	/* 关闭文件 */	
	return 0;
}

应用层的代码比较简单就是实现了从模块读取数据并打印