Linux内核I2C子系统驱动
来源：互联网 发布：淘宝上架员招聘 编辑：程序博客网 时间：2024/05/15 10:01
一、I2C体系结构
Linux的I2C体系结构分为3个组成部分：I2C核心、I2C总线驱动、I2C设备驱动，如下图所示。I2C核心提供总线驱动和设备驱动的注册、注销方法，algorithm；I2C总线驱动对硬件体系结构中适配器的实现，主要包括适配器i2c_adapter、适配器通信算法i2c_algorithm，如果CPU集成了I2C控制器并且linux内核支持这个CPU，那么总线驱动就不用管，比如S3C2440就属于这类情况，在后文中我们将分析它的总线驱动；I2C设备驱动是具体的一个设备(如AT24C02)，挂接在CPU控制的I2C适配器的设备驱动，有了这部分驱动才能使用控制器操作该设备，设备驱动主要包括i2c_driver 和i2c_client数据结构。
在linux-2.6.32.2的include/linux/i2c.h中定义了i2c_adapter、i2c_algorithm、i2c_driver、i2c_client数据结构如下所示，这4个结构体相互之间的关系。
- struct i2c_adapter {
- struct module *owner;
- unsigned int id;
- unsigned int class; /* classes to allow probing for */
- const struct i2c_algorithm *algo; /* the algorithm to access the bus总线通信方法结构体指针 */
- void *algo_data; /* algorithm数据 */
- /* data fields that are valid for all devices */
- u8 level; /* nesting level for lockdep */
- struct mutex bus_lock;
- int timeout; /* in jiffies */
- int retries; /* 重试次数 */
- struct device dev; /* the adapter device */
- int nr;
- char name[48];
- struct completion dev_released;
- };
- struct i2c_algorithm {
- int (*master_xfer)(struct i2c_adapter *adap, struct i2c_msg *msgs,
- int num); /*i2c传输函数指针*/
- int (*smbus_xfer) (struct i2c_adapter *adap, u16 addr,
- unsigned short flags, char read_write,
- u8 command, int size, union i2c_smbus_data *data); /*smbus传输函数指针*/
- /* To determine what the adapter supports */
- u32 (*functionality) (struct i2c_adapter *); /*返回适配器支持的功能*/
- };
- struct i2c_driver {
- unsigned int class;
- int (*attach_adapter)(struct i2c_adapter *); /*依附i2c_adapter函数指针*/
- int (*detach_adapter)(struct i2c_adapter *); /*脱离i2c_adapter函数指针*/
- /* Standard driver model interfaces */
- int (*probe)(struct i2c_client *, const struct i2c_device_id *);
- int (*remove)(struct i2c_client *);
- /* driver model interfaces that don't relate to enumeration */
- void (*shutdown)(struct i2c_client *);
- int (*suspend)(struct i2c_client *, pm_message_t mesg);
- int (*resume)(struct i2c_client *); /* probe，remove，suspend，resume驱动方法重要成员函数 */
- /* a ioctl like command that can be used to perform specific functions
- * with the device.
- */
- int (*command)(struct i2c_client *client, unsigned int cmd, void *arg); /*类似ioctl*/
- struct device_driver driver;
- const struct i2c_device_id *id_table; /* 驱动支持多个设备，这里面就要包含这些设备的ID */
- /* Device detection callback for automatic device creation */
- int (*detect)(struct i2c_client *, int kind, struct i2c_board_info *); /*i2c client脱离函数指针*/
- const struct i2c_client_address_data *address_data;
- struct list_head clients;
- };
- struct i2c_client {
- unsigned short flags; /* div., see below */
- unsigned short addr; /* chip address - NOTE: 7bit 芯片地址 */
- /* addresses are stored in the */
- /* _LOWER_ 7 bits */
- char name[I2C_NAME_SIZE];
- struct i2c_adapter *adapter; /* the adapter we sit on 依附的i2c_adapter */
- struct i2c_driver *driver; /* and our access routines 依附的i2c_driver */
- struct device dev; /* the device structure */
- int irq; /* irq issued by device */
- struct list_head detected;
- };
1、i2c_adapter 与i2c_algorithm，i2c_adapter 对应于物理上的一个适配器，而i2c_algorithm对应一套通信方法。一个I2C适配器需要i2c_algorithm中提供的通信函数来控制适配器上产生特定的访问周期。缺少i2c_algorithm 的i2c_adapter 什么也做不了，因此i2c_adapter 中包含其使用的i2c_algorithm的指针。i2c_algorithm 中的关键函数master_xfer()用于产生I2C 访问周期需要的信号，以i2c_msg（即I2C消息）为单位。i2c_msg结构体也非常关键。
struct i2c_msg {
__u16 addr; /* slave address */
__u16 flags;
#define I2C_M_TEN 0x0010 /* this is a ten bit chip address */
#define I2C_M_RD 0x0001 /* read data, from slave to master */
#define I2C_M_NOSTART 0x4000 /* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_REV_DIR_ADDR 0x2000 /* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_IGNORE_NAK 0x1000 /* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_NO_RD_ACK 0x0800 /* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_RECV_LEN 0x0400 /* length will be first received byte */
__u16 len; /* msg length */
__u8 *buf; /* pointer to msg data */
};
2、i2c_driver 与i2c_client，i2c_driver 对应一套驱动方法，是纯粹的用于辅助作用的数据结构，它不对应于任何的物理实体。i2c_client对应于真实的物理设备，每个I2C设备都需要一个i2c_client来描述。i2c_client一般被包含在I2C字符设备的私有信息结构体中。
3、i2c_adpater 与i2c_client，i2c_adpater 与i2c_client 的关系与I2C 硬件体系中适配器和设备的关系一致，即i2c_client 依附于i2c_adpater。
二、I2C核心
I2C核心是总线驱动和设备驱动的纽带，源码位于drivers/i2c/i2c-core.c,它并不依赖于硬件平台的接口函数，I2C核心中一些重要函数如下：
增加/删除i2c_adapter
int i2c_add_adapter(struct i2c_adapter *adapter)
int i2c_del_adapter(struct i2c_adapter *adapter)
增加/删除i2c_driver
int i2c_register_driver(struct module *owner, struct i2c_driver *driver)
int i2c_add_driver(struct i2c_driver *driver) //调用i2c_register_driver
void i2c_del_driver(struct i2c_driver *driver)
增加/删除i2c_client
struct i2c_client *i2c_new_device(struct i2c_adapter *adap, struct i2c_board_info const *info)
void i2c_unregister_device(struct i2c_client *client)
注：在2.6.30版本之前使用的是i2c_attach_client()和i2c_detach_client()函数。之后attach被merge到了i2c_new_device中，而detach直接被unresister取代。实际上这两个函数内部都是调用了device_register()和device_unregister()
I2C传输、发送接收
int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
int i2c_master_send(struct i2c_client *client,const char *buf ,int count)
int i2c_master_recv(struct i2c_client *client, char *buf ,int count)
i2c_transfer()函数用于进行I2C 适配器和I2C 设备之间的一组消息交互，i2c_master_send()函数和i2c_master_recv()函数内部会调用i2c_transfer()函数分别完成一条写消息和一条读消息，i2c_transfer()本身不能喝硬件完成消息交互，它寻找i2c_adapter对应的i2c_algorithm，要实现数据传送就要实现i2c_algorithm的master_xfer()，在总线驱动中就是重点。
上一篇文章讲述了I2C子系统体系结构，总线驱动、设备驱动的知识点，下面就S3C2440 I2C总线驱动的实现详细讲解，它的源码位于drivers/i2c/busses/i2c-s3c2410.c
一、I2C平台设备资源
IIC驱动中使用的平台设备与前面看门狗、rtc等方式原理相同，但定义路径有所不同，并且设置了额外一些参数。mach_smdk2440.c文件中smdk2440_machine_init函数初始化了平台设备，还对s3c_device_i2c0平台设备进行额外的设置(s3c_i2c0_set_platdata)，s3c_device_i2c0平台设备定义在arch/arm/plat-s3c/dev-i2c0.c。
static void __init smdk2440_machine_init(void)
{
s3c24xx_fb_set_platdata(&smdk2440_fb_info);
s3c_i2c0_set_platdata(NULL);
platform_add_devices(smdk2440_devices, ARRAY_SIZE(smdk2440_devices));
smdk_machine_init();
}
下面是s3c_device_i2c0平台设备相关部分，s3c_i2c0_set_platdata初始化s3c_device_i2c0.dev.platform_data为default_i2c_data0
static struct resource s3c_i2c_resource[] = {
[0] = {
.start = S3C_PA_IIC,
.end = S3C_PA_IIC + SZ_4K - 1,
.flags = IORESOURCE_MEM,
},
[1] = {
.start = IRQ_IIC,
.end = IRQ_IIC,
.flags = IORESOURCE_IRQ,
},
};
struct platform_device s3c_device_i2c0 = {
.name = "s3c2410-i2c",
#ifdef CONFIG_S3C_DEV_I2C1
.id = 0,
#else
.id = -1,
#endif
.num_resources = ARRAY_SIZE(s3c_i2c_resource),
.resource = s3c_i2c_resource,
};
static struct s3c2410_platform_i2c default_i2c_data0 __initdata = {
.flags = 0,
.slave_addr = 0x10,
.frequency = 100*1000,
.sda_delay = 100,
};
void __init s3c_i2c0_set_platdata(struct s3c2410_platform_i2c *pd)
{
struct s3c2410_platform_i2c *npd;
if (!pd)
pd = &default_i2c_data0;
npd = kmemdup(pd, sizeof(struct s3c2410_platform_i2c), GFP_KERNEL);
if (!npd)
printk(KERN_ERR "%s: no memory for platform data\n", __func__);
else if (!npd->cfg_gpio)
npd->cfg_gpio = s3c_i2c0_cfg_gpio;
s3c_device_i2c0.dev.platform_data = npd;
}
void s3c_i2c0_cfg_gpio(struct platform_device *dev)
{ // 位于arch/arm/plat-s3c24xx/setup-i2c.c
s3c2410_gpio_cfgpin(S3C2410_GPE(15), S3C2410_GPE15_IICSDA);
s3c2410_gpio_cfgpin(S3C2410_GPE(14), S3C2410_GPE14_IICSCL);
}
二、总线驱动实现
1.I2C适配器驱动加载卸载
- static int s3c24xx_i2c_calcdivisor(unsigned long clkin, unsigned int wanted,
- unsigned int *div1, unsigned int *divs)
- {
- unsigned int calc_divs = clkin / wanted;
- unsigned int calc_div1;
- if (calc_divs > (16*16))
- calc_div1 = 512;
- else
- calc_div1 = 16;
- calc_divs += calc_div1-1;
- calc_divs /= calc_div1;
- if (calc_divs == 0)
- calc_divs = 1;
- if (calc_divs > 17)
- calc_divs = 17;
- *divs = calc_divs;
- *div1 = calc_div1;
- return clkin / (calc_divs * calc_div1);
- }
- /* s3c24xx_i2c_clockrate
- *
- * work out a divisor for the user requested frequency setting,
- * either by the requested frequency, or scanning the acceptable
- * range of frequencies until something is found
- */
- static int s3c24xx_i2c_clockrate(struct s3c24xx_i2c *i2c, unsigned int *got)
- {
- struct s3c2410_platform_i2c *pdata = i2c->dev->platform_data;
- unsigned long clkin = clk_get_rate(i2c->clk); /* PCLK */
- unsigned int divs, div1;
- unsigned long target_frequency; /* 需要设置速率默认100khz */
- u32 iiccon;
- int freq;
- i2c->clkrate = clkin;
- clkin /= 1000; /* clkin now in KHz */
- dev_dbg(i2c->dev, "pdata desired frequency %lu\n", pdata->frequency);
- target_frequency = pdata->frequency ? pdata->frequency : 100000;
- target_frequency /= 1000; /* Target frequency now in KHz */
- freq = s3c24xx_i2c_calcdivisor(clkin, target_frequency, &div1, &divs); /* 计算出IICCON中Tx clock source selection和Transmit clock value */
- if (freq > target_frequency) {
- dev_err(i2c->dev,
- "Unable to achieve desired frequency %luKHz." \
- " Lowest achievable %dKHz\n", target_frequency, freq);
- return -EINVAL;
- }
- *got = freq;
- iiccon = readl(i2c->regs + S3C2410_IICCON);
- iiccon &= ~(S3C2410_IICCON_SCALEMASK | S3C2410_IICCON_TXDIV_512);
- iiccon |= (divs-1);
- if (div1 == 512)
- iiccon |= S3C2410_IICCON_TXDIV_512;
- writel(iiccon, i2c->regs + S3C2410_IICCON);
- if (s3c24xx_i2c_is2440(i2c)) { /* 2440设置IICLC */
- unsigned long sda_delay;
- if (pdata->sda_delay) {
- sda_delay = (freq / 1000) * pdata->sda_delay;
- sda_delay /= 1000000;
- sda_delay = DIV_ROUND_UP(sda_delay, 5);
- if (sda_delay > 3)
- sda_delay = 3;
- sda_delay |= S3C2410_IICLC_FILTER_ON;
- } else
- sda_delay = 0;
- dev_dbg(i2c->dev, "IICLC=%08lx\n", sda_delay);
- writel(sda_delay, i2c->regs + S3C2440_IICLC);
- }
- return 0;
- }
- #ifdef CONFIG_CPU_FREQ
- #define freq_to_i2c(_n) container_of(_n, struct s3c24xx_i2c, freq_transition)
- static int s3c24xx_i2c_cpufreq_transition(struct notifier_block *nb,
- unsigned long val, void *data)
- {
- struct s3c24xx_i2c *i2c = freq_to_i2c(nb);
- unsigned long flags;
- unsigned int got;
- int delta_f;
- int ret;
- delta_f = clk_get_rate(i2c->clk) - i2c->clkrate;
- /* if we're post-change and the input clock has slowed down
- * or at pre-change and the clock is about to speed up, then
- * adjust our clock rate. <0 is slow, >0 speedup.
- */
- if ((val == CPUFREQ_POSTCHANGE && delta_f < 0) ||
- (val == CPUFREQ_PRECHANGE && delta_f > 0)) {
- spin_lock_irqsave(&i2c->lock, flags);
- ret = s3c24xx_i2c_clockrate(i2c, &got);
- spin_unlock_irqrestore(&i2c->lock, flags);
- if (ret < 0)
- dev_err(i2c->dev, "cannot find frequency\n");
- else
- dev_info(i2c->dev, "setting freq %d\n", got);
- }
- return 0;
- }
- static inline int s3c24xx_i2c_register_cpufreq(struct s3c24xx_i2c *i2c)
- {
- i2c->freq_transition.notifier_call = s3c24xx_i2c_cpufreq_transition;
- return cpufreq_register_notifier(&i2c->freq_transition,
- CPUFREQ_TRANSITION_NOTIFIER);
- }
- static inline void s3c24xx_i2c_deregister_cpufreq(struct s3c24xx_i2c *i2c)
- {
- cpufreq_unregister_notifier(&i2c->freq_transition,
- CPUFREQ_TRANSITION_NOTIFIER);
- }
- #else
- static inline int s3c24xx_i2c_register_cpufreq(struct s3c24xx_i2c *i2c)
- {
- return 0;
- }
- static inline void s3c24xx_i2c_deregister_cpufreq(struct s3c24xx_i2c *i2c)
- {
- }
- #endif
- /* s3c24xx_i2c_init
- *
- * initialise the controller, set the IO lines and frequency
- */
- static int s3c24xx_i2c_init(struct s3c24xx_i2c *i2c)
- {
- unsigned long iicon = S3C2410_IICCON_IRQEN | S3C2410_IICCON_ACKEN;
- struct s3c2410_platform_i2c *pdata;
- unsigned int freq;
- /* get the plafrom data */
- pdata = i2c->dev->platform_data; /* 获取platform_data */
- /* inititalise the gpio */
- if (pdata->cfg_gpio)
- pdata->cfg_gpio(to_platform_device(i2c->dev));
- /* write slave address */
- writeb(pdata->slave_addr, i2c->regs + S3C2410_IICADD);
- dev_info(i2c->dev, "slave address 0x%02x\n", pdata->slave_addr);
- writel(iicon, i2c->regs + S3C2410_IICCON);
- /* we need to work out the divisors for the clock... */
- if (s3c24xx_i2c_clockrate(i2c, &freq) != 0) { /* 设置i2c速率 */
- writel(0, i2c->regs + S3C2410_IICCON);
- dev_err(i2c->dev, "cannot meet bus frequency required\n");
- return -EINVAL;
- }
- /* todo - check that the i2c lines aren't being dragged anywhere */
- dev_info(i2c->dev, "bus frequency set to %d KHz\n", freq);
- dev_dbg(i2c->dev, "S3C2410_IICCON=0x%02lx\n", iicon);
- return 0;
- }
- /* s3c24xx_i2c_probe
- *
- * called by the bus driver when a suitable device is found
- */
- static int s3c24xx_i2c_probe(struct platform_device *pdev)
- {
- struct s3c24xx_i2c *i2c;
- struct s3c2410_platform_i2c *pdata;
- struct resource *res;
- int ret;
- pdata = pdev->dev.platform_data; /* 在平台设备资源中初始化了platform_data，关于platform_data参考前一节 */
- if (!pdata) {
- dev_err(&pdev->dev, "no platform data\n");
- return -EINVAL;
- }
- i2c = kzalloc(sizeof(struct s3c24xx_i2c), GFP_KERNEL); /* s3c24xx_i2c分配空间 */
- if (!i2c) {
- dev_err(&pdev->dev, "no memory for state\n");
- return -ENOMEM;
- }
- strlcpy(i2c->adap.name, "s3c2410-i2c", sizeof(i2c->adap.name)); /* s3c24xx_i2c初始化 */
- i2c->adap.owner = THIS_MODULE;
- i2c->adap.algo = &s3c24xx_i2c_algorithm; /* 通信方法，下一节重点介绍 */
- i2c->adap.retries = 2;
- i2c->adap.class = I2C_CLASS_HWMON | I2C_CLASS_SPD;
- i2c->tx_setup = 50;
- spin_lock_init(&i2c->lock);
- init_waitqueue_head(&i2c->wait);
- /* find the clock and enable it */
- i2c->dev = &pdev->dev;
- i2c->clk = clk_get(&pdev->dev, "i2c"); /* 时钟 */
- if (IS_ERR(i2c->clk)) {
- dev_err(&pdev->dev, "cannot get clock\n");
- ret = -ENOENT;
- goto err_noclk;
- }
- dev_dbg(&pdev->dev, "clock source %p\n", i2c->clk);
- clk_enable(i2c->clk);
- /* map the registers */
- res = platform_get_resource(pdev, IORESOURCE_MEM, 0); /* 寄存器映射 */
- if (res == NULL) {
- dev_err(&pdev->dev, "cannot find IO resource\n");
- ret = -ENOENT;
- goto err_clk;
- }
- i2c->ioarea = request_mem_region(res->start, resource_size(res),
- pdev->name);
- if (i2c->ioarea == NULL) {
- dev_err(&pdev->dev, "cannot request IO\n");
- ret = -ENXIO;
- goto err_clk;
- }
- i2c->regs = ioremap(res->start, resource_size(res));
- if (i2c->regs == NULL) {
- dev_err(&pdev->dev, "cannot map IO\n");
- ret = -ENXIO;
- goto err_ioarea;
- }
- dev_dbg(&pdev->dev, "registers %p (%p, %p)\n",
- i2c->regs, i2c->ioarea, res);
- /* setup info block for the i2c core */
- i2c->adap.algo_data = i2c;
- i2c->adap.dev.parent = &pdev->dev;
- /* initialise the i2c controller */
- ret = s3c24xx_i2c_init(i2c); /* 初始化 */
- if (ret != 0)
- goto err_iomap;
- /* find the IRQ for this unit (note, this relies on the init call to
- * ensure no current IRQs pending
- */
- i2c->irq = ret = platform_get_irq(pdev, 0); /* 中断申请 */
- if (ret <= 0) {
- dev_err(&pdev->dev, "cannot find IRQ\n");
- goto err_iomap;
- }
- ret = request_irq(i2c->irq, s3c24xx_i2c_irq, IRQF_DISABLED,
- dev_name(&pdev->dev), i2c);
- if (ret != 0) {
- dev_err(&pdev->dev, "cannot claim IRQ %d\n", i2c->irq);
- goto err_iomap;
- }
- ret = s3c24xx_i2c_register_cpufreq(i2c); /* 关于cpufreq没明白，有关cpufreq可以暂时不管 */
- if (ret < 0) {
- dev_err(&pdev->dev, "failed to register cpufreq notifier\n");
- goto err_irq;
- }
- /* Note, previous versions of the driver used i2c_add_adapter()
- * to add the bus at any number. We now pass the bus number via
- * the platform data, so if unset it will now default to always
- * being bus 0.
- */
- i2c->adap.nr = pdata->bus_num;
- /*调用了i2c-core中的i2c_add_adapter函数来添加一个i2c控制器,i2c_add_numbered_adapter和i2c_add_adapter的
- 区别在于前者用来添加一个在CPU内部集成的适配器，而后者用来添加一个CPU外部的适配器。显然这里应该用前者 */
- ret = i2c_add_numbered_adapter(&i2c->adap);
- if (ret < 0) {
- dev_err(&pdev->dev, "failed to add bus to i2c core\n");
- goto err_cpufreq;
- }
- platform_set_drvdata(pdev, i2c);
- dev_info(&pdev->dev, "%s: S3C I2C adapter\n", dev_name(&i2c->adap.dev));
- return 0;
- err_cpufreq:
- s3c24xx_i2c_deregister_cpufreq(i2c);
- err_irq:
- free_irq(i2c->irq, i2c);
- err_iomap:
- iounmap(i2c->regs);
- err_ioarea:
- release_resource(i2c->ioarea);
- kfree(i2c->ioarea);
- err_clk:
- clk_disable(i2c->clk);
- clk_put(i2c->clk);
- err_noclk:
- kfree(i2c);
- return ret;
- }
- /* s3c24xx_i2c_remove
- *
- * called when device is removed from the bus
- */
- static int s3c24xx_i2c_remove(struct platform_device *pdev)
- {
- struct s3c24xx_i2c *i2c = platform_get_drvdata(pdev);
- s3c24xx_i2c_deregister_cpufreq(i2c);
- i2c_del_adapter(&i2c->adap); /* 删除adapter*/
- free_irq(i2c->irq, i2c);
- clk_disable(i2c->clk);
- clk_put(i2c->clk);
- iounmap(i2c->regs);
- release_resource(i2c->ioarea);
- kfree(i2c->ioarea);
- kfree(i2c);
- return 0;
- }
- #ifdef CONFIG_PM
- static int s3c24xx_i2c_suspend_noirq(struct device *dev)
- {
- struct platform_device *pdev = to_platform_device(dev);
- struct s3c24xx_i2c *i2c = platform_get_drvdata(pdev);
- i2c->suspended = 1;
- return 0;
- }
- static int s3c24xx_i2c_resume(struct device *dev)
- {
- struct platform_device *pdev = to_platform_device(dev);
- struct s3c24xx_i2c *i2c = platform_get_drvdata(pdev);
- i2c->suspended = 0;
- s3c24xx_i2c_init(i2c);
- return 0;
- }
- static struct dev_pm_ops s3c24xx_i2c_dev_pm_ops = {
- .suspend_noirq = s3c24xx_i2c_suspend_noirq,
- .resume = s3c24xx_i2c_resume,
- };
- #define S3C24XX_DEV_PM_OPS (&s3c24xx_i2c_dev_pm_ops)
- #else
- #define S3C24XX_DEV_PM_OPS NULL
- #endif
- /* device driver for platform bus bits */
- static struct platform_device_id s3c24xx_driver_ids[] = {
- {
- .name = "s3c2410-i2c",
- .driver_data = TYPE_S3C2410,
- }, {
- .name = "s3c2440-i2c",
- .driver_data = TYPE_S3C2440,
- }, { },
- };
- MODULE_DEVICE_TABLE(platform, s3c24xx_driver_ids);
- static struct platform_driver s3c24xx_i2c_driver = {
- .probe = s3c24xx_i2c_probe,
- .remove = s3c24xx_i2c_remove,
- .id_table = s3c24xx_driver_ids, //解释参见代码后面说明
- .driver = {
- .owner = THIS_MODULE,
- .name = "s3c-i2c",
- .pm = S3C24XX_DEV_PM_OPS,
- },
- };
- static int __init i2c_adap_s3c_init(void)
- {
- return platform_driver_register(&s3c24xx_i2c_driver);
- }
- subsys_initcall(i2c_adap_s3c_init);
- static void __exit i2c_adap_s3c_exit(void)
- {
- platform_driver_unregister(&s3c24xx_i2c_driver);
- }
- module_exit(i2c_adap_s3c_exit);
- MODULE_DESCRIPTION("S3C24XX I2C Bus driver");
- MODULE_AUTHOR("Ben Dooks, <ben@simtec.co.uk>");
- MODULE_LICENSE("GPL");
i2c_adap_s3c_init注册i2c平台驱动s3c24xx_i2c_driver，它是platform_driver结构体，不要误解为i2c_driver。同时还实现了probe、remove、id_table、driver，其中suspend、resume在driver中实现。i2c_adap_s3c_exit注销s3c24xx_i2c_driver。
关于平台驱动s3c24xx_i2c_driver中名字为s3c_i2c与平台设备中名字s3c2410-i2c不一样，怎么匹配？这里主要在于id_table，s3c24xx_driver_ids包含了驱动所支持的设备ID表，判断这个表中的名字与平台设备中名字一致，则匹配成功。
2.I2C通信方法
- #include <linux/kernel.h>
- #include <linux/module.h>
- #include <linux/i2c.h>
- #include <linux/i2c-id.h>
- #include <linux/init.h>
- #include <linux/time.h>
- #include <linux/interrupt.h>
- #include <linux/delay.h>
- #include <linux/errno.h>
- #include <linux/err.h>
- #include <linux/platform_device.h>
- #include <linux/clk.h>
- #include <linux/cpufreq.h>
- #include <asm/irq.h>
- #include <asm/io.h>
- #include <plat/regs-iic.h>
- #include <plat/iic.h>
- /* i2c controller state */
- enum s3c24xx_i2c_state {
- STATE_IDLE,
- STATE_START,
- STATE_READ,
- STATE_WRITE,
- STATE_STOP
- };
- enum s3c24xx_i2c_type {
- TYPE_S3C2410,
- TYPE_S3C2440,
- };
- struct s3c24xx_i2c {
- spinlock_t lock;
- wait_queue_head_t wait;
- unsigned int suspended:1;
- struct i2c_msg *msg;
- unsigned int msg_num;
- unsigned int msg_idx;
- unsigned int msg_ptr;
- unsigned int tx_setup;
- unsigned int irq;
- enum s3c24xx_i2c_state state;
- unsigned long clkrate;
- void __iomem *regs;
- struct clk *clk;
- struct device *dev;
- struct resource *ioarea;
- struct i2c_adapter adap;
- #ifdef CONFIG_CPU_FREQ
- struct notifier_block freq_transition;
- #endif
- };
- /* default platform data removed, dev should always carry data. */
- /* s3c24xx_i2c_is2440()
- *
- * return true is this is an s3c2440
- */
- static inline int s3c24xx_i2c_is2440(struct s3c24xx_i2c *i2c)
- {
- struct platform_device *pdev = to_platform_device(i2c->dev);
- enum s3c24xx_i2c_type type;
- type = platform_get_device_id(pdev)->driver_data;
- return type == TYPE_S3C2440;
- }
- /* s3c24xx_i2c_master_complete
- *
- * complete the message and wake up the caller, using the given return code,
- * or zero to mean ok.
- */
- static inline void s3c24xx_i2c_master_complete(struct s3c24xx_i2c *i2c, int ret)
- {
- dev_dbg(i2c->dev, "master_complete %d\n", ret);
- i2c->msg_ptr = 0;
- i2c->msg = NULL;
- i2c->msg_idx++;
- i2c->msg_num = 0;
- if (ret)
- i2c->msg_idx = ret;
- wake_up(&i2c->wait);
- }
- static inline void s3c24xx_i2c_disable_ack(struct s3c24xx_i2c *i2c)
- {
- unsigned long tmp;
- tmp = readl(i2c->regs + S3C2410_IICCON);
- writel(tmp & ~S3C2410_IICCON_ACKEN, i2c->regs + S3C2410_IICCON);
- }
- static inline void s3c24xx_i2c_enable_ack(struct s3c24xx_i2c *i2c)
- {
- unsigned long tmp;
- tmp = readl(i2c->regs + S3C2410_IICCON);
- writel(tmp | S3C2410_IICCON_ACKEN, i2c->regs + S3C2410_IICCON);
- }
- /* irq enable/disable functions */
- static inline void s3c24xx_i2c_disable_irq(struct s3c24xx_i2c *i2c)
- {
- unsigned long tmp;
- tmp = readl(i2c->regs + S3C2410_IICCON);
- writel(tmp & ~S3C2410_IICCON_IRQEN, i2c->regs + S3C2410_IICCON);
- }
- static inline void s3c24xx_i2c_enable_irq(struct s3c24xx_i2c *i2c)
- {
- unsigned long tmp;
- tmp = readl(i2c->regs + S3C2410_IICCON);
- writel(tmp | S3C2410_IICCON_IRQEN, i2c->regs + S3C2410_IICCON);
- }
- /* s3c24xx_i2c_message_start
- *
- * put the start of a message onto the bus
- */
- static void s3c24xx_i2c_message_start(struct s3c24xx_i2c *i2c,
- struct i2c_msg *msg)
- {
- unsigned int addr = (msg->addr & 0x7f) << 1;
- unsigned long stat;
- unsigned long iiccon;
- stat = 0;
- stat |= S3C2410_IICSTAT_TXRXEN; /* 使能TXRX */
- if (msg->flags & I2C_M_RD) { /* 设备地址 */
- stat |= S3C2410_IICSTAT_MASTER_RX;
- addr |= 1;
- } else
- stat |= S3C2410_IICSTAT_MASTER_TX;
- if (msg->flags & I2C_M_REV_DIR_ADDR)
- addr ^= 1;
- /* todo - check for wether ack wanted or not */
- s3c24xx_i2c_enable_ack(i2c); /* 使能ack */
- iiccon = readl(i2c->regs + S3C2410_IICCON);
- writel(stat, i2c->regs + S3C2410_IICSTAT);
- dev_dbg(i2c->dev, "START: %08lx to IICSTAT, %02x to DS\n", stat, addr);
- writeb(addr, i2c->regs + S3C2410_IICDS); /* 写设备地址 */
- /* delay here to ensure the data byte has gotten onto the bus
- * before the transaction is started */
- ndelay(i2c->tx_setup);
- dev_dbg(i2c->dev, "iiccon, %08lx\n", iiccon);
- writel(iiccon, i2c->regs + S3C2410_IICCON);
- stat |= S3C2410_IICSTAT_START; /* 启动i2c，当设备地址发送后就会进入中断，在中断中根据不同状态进行读写操作 */
- writel(stat, i2c->regs + S3C2410_IICSTAT);
- }
- static inline void s3c24xx_i2c_stop(struct s3c24xx_i2c *i2c, int ret)
- {
- unsigned long iicstat = readl(i2c->regs + S3C2410_IICSTAT);
- dev_dbg(i2c->dev, "STOP\n");
- /* stop the transfer */
- iicstat &= ~S3C2410_IICSTAT_START;
- writel(iicstat, i2c->regs + S3C2410_IICSTAT);
- i2c->state = STATE_STOP;
- s3c24xx_i2c_master_complete(i2c, ret);
- s3c24xx_i2c_disable_irq(i2c);
- }
- /* helper functions to determine the current state in the set of
- * messages we are sending */
- /* 关于以下三个函数功能区别，后文详解 */
- /* is_lastmsg()
- *
- * returns TRUE if the current message is the last in the set
- */
- static inline int is_lastmsg(struct s3c24xx_i2c *i2c)
- {
- return i2c->msg_idx >= (i2c->msg_num - 1);
- }
- /* is_msglast
- *
- * returns TRUE if we this is the last byte in the current message
- */
- static inline int is_msglast(struct s3c24xx_i2c *i2c)
- {
- return i2c->msg_ptr == i2c->msg->len-1;
- }
- /* is_msgend
- *
- * returns TRUE if we reached the end of the current message
- */
- static inline int is_msgend(struct s3c24xx_i2c *i2c)
- {
- return i2c->msg_ptr >= i2c->msg->len;
- }
- /* i2s_s3c_irq_nextbyte
- *
- * process an interrupt and work out what to do
- */
- static int i2s_s3c_irq_nextbyte(struct s3c24xx_i2c *i2c, unsigned long iicstat)
- {
- /* 此函数比较复杂，在后文中将举一个具体例子来说明整个过程 */
- unsigned long tmp;
- unsigned char byte;
- int ret = 0;
- switch (i2c->state) {
- case STATE_IDLE:
- dev_err(i2c->dev, "%s: called in STATE_IDLE\n", __func__);
- goto out;
- break;
- case STATE_STOP:
- dev_err(i2c->dev, "%s: called in STATE_STOP\n", __func__);
- s3c24xx_i2c_disable_irq(i2c);
- goto out_ack;
- case STATE_START:
- /* last thing we did was send a start condition on the
- * bus, or started a new i2c message
- */
- if (iicstat & S3C2410_IICSTAT_LASTBIT &&
- !(i2c->msg->flags & I2C_M_IGNORE_NAK)) {
- /* ack was not received... */
- dev_dbg(i2c->dev, "ack was not received\n");
- s3c24xx_i2c_stop(i2c, -ENXIO);
- goto out_ack;
- }
- if (i2c->msg->flags & I2C_M_RD)
- i2c->state = STATE_READ;
- else
- i2c->state = STATE_WRITE;
- /* terminate the transfer if there is nothing to do
- * as this is used by the i2c probe to find devices. */
- if (is_lastmsg(i2c) && i2c->msg->len == 0) {
- s3c24xx_i2c_stop(i2c, 0);
- goto out_ack;
- }
- if (i2c->state == STATE_READ)
- goto prepare_read;
- /* fall through to the write state, as we will need to
- * send a byte as well */
- case STATE_WRITE:
- /* we are writing data to the device... check for the
- * end of the message, and if so, work out what to do
- */
- if (!(i2c->msg->flags & I2C_M_IGNORE_NAK)) {
- if (iicstat & S3C2410_IICSTAT_LASTBIT) {
- dev_dbg(i2c->dev, "WRITE: No Ack\n");
- s3c24xx_i2c_stop(i2c, -ECONNREFUSED);
- goto out_ack;
- }
- }
- retry_write:
- if (!is_msgend(i2c)) {
- byte = i2c->msg->buf[i2c->msg_ptr++];
- writeb(byte, i2c->regs + S3C2410_IICDS);
- /* delay after writing the byte to allow the
- * data setup time on the bus, as writing the
- * data to the register causes the first bit
- * to appear on SDA, and SCL will change as
- * soon as the interrupt is acknowledged */
- ndelay(i2c->tx_setup);
- } else if (!is_lastmsg(i2c)) {
- /* we need to go to the next i2c message */
- dev_dbg(i2c->dev, "WRITE: Next Message\n");
- i2c->msg_ptr = 0;
- i2c->msg_idx++;
- i2c->msg++;
- /* check to see if we need to do another message */
- if (i2c->msg->flags & I2C_M_NOSTART) {
- if (i2c->msg->flags & I2C_M_RD) {
- /* cannot do this, the controller
- * forces us to send a new START
- * when we change direction */
- s3c24xx_i2c_stop(i2c, -EINVAL);
- }
- goto retry_write;
- } else {
- /* send the new start */
- s3c24xx_i2c_message_start(i2c, i2c->msg);
- i2c->state = STATE_START;
- }
- } else {
- /* send stop */
- s3c24xx_i2c_stop(i2c, 0);
- }
- break;
- case STATE_READ:
- /* we have a byte of data in the data register, do
- * something with it, and then work out wether we are
- * going to do any more read/write
- */
- byte = readb(i2c->regs + S3C2410_IICDS);
- i2c->msg->buf[i2c->msg_ptr++] = byte;
- prepare_read:
- if (is_msglast(i2c)) {
- /* last byte of buffer */
- if (is_lastmsg(i2c))
- s3c24xx_i2c_disable_ack(i2c);
- } else if (is_msgend(i2c)) {
- /* ok, we've read the entire buffer, see if there
- * is anything else we need to do */
- if (is_lastmsg(i2c)) {
- /* last message, send stop and complete */
- dev_dbg(i2c->dev, "READ: Send Stop\n");
- s3c24xx_i2c_stop(i2c, 0);
- } else {
- /* go to the next transfer */
- dev_dbg(i2c->dev, "READ: Next Transfer\n");
- i2c->msg_ptr = 0;
- i2c->msg_idx++;
- i2c->msg++;
- }
- }
- break;
- }
- /* acknowlegde the IRQ and get back on with the work */
- out_ack: /* 退出时请pend flag */
- tmp = readl(i2c->regs + S3C2410_IICCON);
- tmp &= ~S3C2410_IICCON_IRQPEND;
- writel(tmp, i2c->regs + S3C2410_IICCON);
- out:
- return ret;
- }
- /* s3c24xx_i2c_irq
- *
- * top level IRQ servicing routine
- */
- static irqreturn_t s3c24xx_i2c_irq(int irqno, void *dev_id)
- {
- /* 中断第一次进入在调用s3c24xx_i2c_message_start写入设备地址后 */
- struct s3c24xx_i2c *i2c = dev_id;
- unsigned long status;
- unsigned long tmp;
- status = readl(i2c->regs + S3C2410_IICSTAT);
- if (status & S3C2410_IICSTAT_ARBITR) {
- /* deal with arbitration loss */
- dev_err(i2c->dev, "deal with arbitration loss\n");
- }
- if (i2c->state == STATE_IDLE) {
- dev_dbg(i2c->dev, "IRQ: error i2c->state == IDLE\n");
- tmp = readl(i2c->regs + S3C2410_IICCON);
- tmp &= ~S3C2410_IICCON_IRQPEND;
- writel(tmp, i2c->regs + S3C2410_IICCON);
- goto out;
- }
- /* pretty much this leaves us with the fact that we've
- * transmitted or received whatever byte we last sent */
- i2s_s3c_irq_nextbyte(i2c, status); /* 根据不同状态步步推进读写操作，i2s_s3c_irq_nextbyte难点 */
- out:
- return IRQ_HANDLED;
- }
- /* s3c24xx_i2c_set_master
- *
- * get the i2c bus for a master transaction
- */
- static int s3c24xx_i2c_set_master(struct s3c24xx_i2c *i2c)
- {
- unsigned long iicstat;
- int timeout = 400;
- while (timeout-- > 0) {
- iicstat = readl(i2c->regs + S3C2410_IICSTAT);
- if (!(iicstat & S3C2410_IICSTAT_BUSBUSY))
- return 0;
- msleep(1);
- }
- return -ETIMEDOUT;
- }
- /* s3c24xx_i2c_doxfer
- *
- * this starts an i2c transfer
- */
- static int s3c24xx_i2c_doxfer(struct s3c24xx_i2c *i2c,
- struct i2c_msg *msgs, int num)
- {
- unsigned long timeout;
- int ret;
- if (i2c->suspended)
- return -EIO;
- ret = s3c24xx_i2c_set_master(i2c); /* 检查i2c总线状态 */
- if (ret != 0) {
- dev_err(i2c->dev, "cannot get bus (error %d)\n", ret);
- ret = -EAGAIN;
- goto out;
- }
- spin_lock_irq(&i2c->lock);
- i2c->msg = msgs; /* 把消息写入i2c结构体 */
- i2c->msg_num = num;
- i2c->msg_ptr = 0;
- i2c->msg_idx = 0;
- i2c->state = STATE_START;
- s3c24xx_i2c_enable_irq(i2c); /* 使能中断*/
- s3c24xx_i2c_message_start(i2c, msgs); /* 写设备地址，启动i2c */
- spin_unlock_irq(&i2c->lock);
- timeout = wait_event_timeout(i2c->wait, i2c->msg_num == 0, HZ * 5); /* 等待消息传输完成，否则超时 */
- ret = i2c->msg_idx; /* 成功传输消息条数 */
- /* having these next two as dev_err() makes life very
- * noisy when doing an i2cdetect */
- if (timeout == 0)
- dev_dbg(i2c->dev, "timeout\n");
- else if (ret != num) /* 如果ret不等于原有消息条数，传输失败 */
- dev_dbg(i2c->dev, "incomplete xfer (%d)\n", ret);
- /* ensure the stop has been through the bus */
- msleep(1);
- out:
- return ret;
- }
- /* s3c24xx_i2c_xfer
- *
- * first port of call from the i2c bus code when an message needs
- * transferring across the i2c bus.
- */
- static int s3c24xx_i2c_xfer(struct i2c_adapter *adap,
- struct i2c_msg *msgs, int num)
- {
- struct s3c24xx_i2c *i2c = (struct s3c24xx_i2c *)adap->algo_data;
- int retry;
- int ret;
- for (retry = 0; retry < adap->retries; retry++) { /* 传输不成功重复次数 */
- ret = s3c24xx_i2c_doxfer(i2c, msgs, num); /* 重点在这里实现 */
- if (ret != -EAGAIN)
- return ret;
- dev_dbg(i2c->dev, "Retrying transmission (%d)\n", retry);
- udelay(100);
- }
- return -EREMOTEIO;
- }
- /* declare our i2c functionality */
- static u32 s3c24xx_i2c_func(struct i2c_adapter *adap)
- { /* 支持的功能，定义在i2c.h */
- return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL | I2C_FUNC_PROTOCOL_MANGLING;
- }
- /* i2c bus registration info */
- static const struct i2c_algorithm s3c24xx_i2c_algorithm = {
- .master_xfer = s3c24xx_i2c_xfer,
- .functionality = s3c24xx_i2c_func,
- };
I2C适配器的通信方法整个驱动的重点，主要实现i2c_algorithm的master_xfer()和functionality()。s3c24xx_i2c_xfer中调用了s3c24xx_i2c_doxfer，然后启动i2c，并且通过中断s3c24xx_i2c_irq和i2s_s3c_irq_nextbyte来一步步推进传输工作。
通信方法传输是以消息为单位的，所有先了解消息结构体。消息i2c_msg包括地址、标志、一条消息包含的数据及长度。
struct i2c_msg {
__u16 addr; /* slave address */
__u16 flags;
#define I2C_M_TEN 0x0010 /* this is a ten bit chip address */
#define I2C_M_RD 0x0001 /* read data, from slave to master */
#define I2C_M_NOSTART 0x4000 /* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_REV_DIR_ADDR 0x2000 /* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_IGNORE_NAK 0x1000 /* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_NO_RD_ACK 0x0800 /* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_RECV_LEN 0x0400 /* length will be first received byte */
__u16 len; /* msg length */
__u8 *buf; /* pointer to msg data */
};
代码中提到的is_lastmsg、is_msglast、is_msgend到底判断是什么？在s3c24xx_i2c中定义的struct i2c_msg *msg看出可以包含多条消息，而一条消息有可能包含多个数据，比如对于AT24c02页写就包含多个数据。is_lastmsg判断是否是消息中最后一条，使用了变量msg_idx；is_msglast判断是否一条消息中最后一个数据，is_msgend判断是否是一条消息全部完成，所以这两个函数使用变量时msg_ptr。
下面就根据AT24C02具体的讲解s3c24xx_i2c_irq和i2s_s3c_irq_nextbyte如何实现传输。
任意地址字节写时序如上所示，只需要一条消息即可。其中flag位为写，写0即可，消息包括两个数据目标地址、数据，消息如下所示。
struct i2c_msg *msg;
msg=malloc(sizeof(struct i2c_msg));
msg.len=2; // 1个目标地址和1个数据
msg.addr=0x50; // 设备地址
msg.flags=0; // write
msg.buf=(unsigned char*)malloc(2);
msg.buf[0]=0x10;// 目标地址
msg.buf[1]=0x58;// the data to write
s3c24xx_i2c_xfer中调用了s3c24xx_i2c_doxfer，在s3c24xx_i2c_doxfer中把消息传入i2c->msg，使能中断，置i2c->state 为STATE_START，调用s3c24xx_i2c_message_start启动i2c发送设备地址，就等待中断来做后续工作。当设备地址发送后就会进入中断，继续进入i2s_s3c_irq_nextbyte的STATE_START，判断消息为写，置i2c->state 为STATE_WRITE，跳入STATE_WRITE，在retry_write这一段中，if先判断是否一条消息所有数据发送完，没发送完，则每次发送一条等待下次中断进入，每发送一个数据都要清pend位；发送完else if判断是否最后一条消息，如果不是则要指针指向下一条消息继续if的步骤；最后else为发送完成，停止i2c。针对任意字节写只有一条消息，if中发送两次就完成本条消息传输。
任意地址字节读时序如上所示，需两条消息。第一条，写目标地址，flag位为写；第二条，读取数据，flag位为读，第一条与第二条消息之间要发送START。
struct i2c_msg *msgs;
msgs=malloc(2*sizeof(struct i2c_msg));
msgs[0].len=1; // 目标地址
msgs[0].addr=0x50; // 设备地址
msgs[0].flags=0; // write
msgs[0].buf=(unsigned char*)malloc(1);
msgs[0].buf[0]=0x10; // 目标地址
msgs[1].len=1; // 读出的数据
msgs[1].addr=0x50; // 设备地址
msgs[1].flags=I2C_M_RD; // read
msgs[1].buf=(unsigned char*)malloc(1);
msgs[1].buf[0]=0;// 初始化读缓冲
直接从中断开始讲，发送设备地址后，进入STATE_START，判断第一条消息为写，置i2c->state 为STATE_WRITE，跳入STATE_WRITE，第一条消息有一个数据，发送完成后，在else if中判断不是此条消息不是最后一条，就会执行else if中指向下一条消息，s3c24xx_i2c_message_start重新发送START，置i2c->state 为STATE_START。下次进入中跳到STATE_START，判断第二条消息为读，置i2c->state 为STATE_READ跳入STATE_READ，第二条消息只有一个数据，关闭ack，接收一个字节，停止i2c。看完这两个例子，再看
当适配器加载到内核后，就针对具体设备编写I2C设备驱动。编写设备驱动有两种方法，一种是利用系统提供的i2c-dev.c实现，另一种为i2c编写一个独立的设备驱动。
一、i2c-dev.c控制i2c设备
i2c-dev.c没有针对具体设备来设计，提供了通用i2cdev_read()、i2cdev_write()函数来对应用户空间要使用的read()和write()文件操作接口，这两个函数分别调用I2C 核心的i2c_master_recv()和i2c_master_send()函数来构造一条I2C 消息并引发适配器algorithm 通信函数的调用，完成消息的传输。但是i2c_read()、i2c_write()对于一些复杂消息(eeprom字节读ReStart模式)并不太适用，针对以上情况，可以使用i2cdev_ioctl()实现消息组的传输，通过I2C_RDWR IOCTL命令实现。
常用的IOCTL包括包括I2C_SLAVE（设置从设备地址）、I2C_RETRIES（没有收到设备ACK 情况下的重试次数，默认为1）、I2C_TIMEOUT（超时）以及I2C_RDWR等。应用程序通过i2c_rdwr_ioctl_data结构体来给内核传递消息，结构体定义如下
struct i2c_rdwr_ioctl_data {
struct i2c_msg __user *msgs; /* pointers to i2c_msgs */
__u32 nmsgs; /* number of i2c_msgs */
};
下面是利用i2c_dev.c操作i2c设备AT24C02具体的代码，这种方法是从应用层完成i2c设备驱动，代码摘自http://blog.csdn.net/hongtao_liu/article/details/4964244
- #include <stdio.h>
- #include <linux/types.h>
- #include <stdlib.h>
- #include <fcntl.h>
- #include <unistd.h>
- #include <sys/types.h>
- #include <sys/ioctl.h>
- #include <errno.h>
- #define I2C_RETRIES 0x0701
- #define I2C_TIMEOUT 0x0702
- #define I2C_RDWR 0x0707
- /*********参数定义与内核一致，路径include/linux/i2c-dev.h*******/
- struct i2c_msg
- {
- unsigned short addr;
- nsigned short flags;
- #define I2C_M_TEN 0x0010
- #define I2C_M_RD 0x0001
- unsigned short len;
- unsigned char *buf;
- };
- struct i2c_rdwr_ioctl_data
- {
- struct i2c_msg *msgs;
- int nmsgs;
- /* nmsgs这个数量决定了有多少开始信号，对于“单开始时序”，取1*/
- };
- int main()
- {
- int fd,ret;
- struct i2c_rdwr_ioctl_data e2prom_data;
- fd=open("/dev/i2c-0",O_RDWR);
- /*
- */dev/i2c-0是在注册i2c-dev.c后产生的，代表一个可操作的适配器。如果不使用i2c-dev.c
- *的方式，就没有，也不需要这个节点。
- */
- if(fd<0)
- {
- perror("open error");
- }
- e2prom_data.nmsgs=2;
- /*
- *因为操作时序中，最多是用到2个开始信号（字节读操作中），所以此将
- *e2prom_data.nmsgs配置为2
- */
- e2prom_data.msgs=(struct i2c_msg*)malloc(e2prom_data.nmsgs*sizeof(struct i2c_msg));
- if(!e2prom_data.msgs)
- {
- perror("malloc error");
- exit(1);
- }
- ioctl(fd,I2C_TIMEOUT,1);/*超时时间*/
- ioctl(fd,I2C_RETRIES,2);/*重复次数*/
- /***write data to e2prom**/
- e2prom_data.nmsgs=1;
- (e2prom_data.msgs[0]).len=2; //1个 e2prom 写入目标的地址和1个数据
- (e2prom_data.msgs[0]).addr=0x50;//e2prom 设备地址
- (e2prom_data.msgs[0]).flags=0; //write
- (e2prom_data.msgs[0]).buf=(unsigned char*)malloc(2);
- (e2prom_data.msgs[0]).buf[0]=0x10;// e2prom 写入目标的地址
- (e2prom_data.msgs[0]).buf[1]=0x58;//the data to write
- ret=ioctl(fd,I2C_RDWR,(unsigned long)&e2prom_data);
- if(ret<0)
- {
- perror("ioctl error1");
- }
- sleep(1);
- /******read data from e2prom*******/
- e2prom_data.nmsgs=2;
- (e2prom_data.msgs[0]).len=1; //e2prom 目标数据的地址
- (e2prom_data.msgs[0]).addr=0x50; // e2prom 设备地址
- (e2prom_data.msgs[0]).flags=0;//write
- (e2prom_data.msgs[0]).buf[0]=0x10;//e2prom数据地址
- (e2prom_data.msgs[1]).len=1;//读出的数据
- (e2prom_data.msgs[1]).addr=0x50;// e2prom 设备地址
- (e2prom_data.msgs[1]).flags=I2C_M_RD;//read
- (e2prom_data.msgs[1]).buf=(unsigned char*)malloc(1);//存放返回值的地址。
- (e2prom_data.msgs[1]).buf[0]=0;//初始化读缓冲
- ret=ioctl(fd,I2C_RDWR,(unsigned long)&e2prom_data);
- if(ret<0)
- {
- perror("ioctl error2");
- }
- printf("buff[0]=%x/n",(e2prom_data.msgs[1]).buf[0]);
- /***打印读出的值，没错的话，就应该是前面写的0x58了***/
- close(fd);
- return 0;
- }
二、内核中编写i2c设备驱动
内核编写i2c设备驱动支持两种方式：Adapter方式（LEGACY）和Probe方式（new style）。
1.legacy方式
此方法驱动需要自己创建i2c_client，并且要知道芯片的地址，在内核目录documentation/i2c/upgrading-clients中有一个例程。
i2c_driver构建
static struct i2c_driver at24c02_driver = {
.driver = {
.name = "at24c02",
},
.id = I2C_DRIVERID_EEPROM,
.attach_adapter = at24c02_attach_adapter,
.detach_client = at24c02_detach_client,
};
I2C设备驱动的加载与卸载函数模板
static int __init at24c02_init(void)
{
return i2c_add_driver(&at24c02_driver);
}
i2c_add_driver的执行回引发i2c_driver结构体at24c02_attach_adapter的执行，若内核中注册了i2c适配器，就顺序调用这些适配器来连接i2c设备，at24c02_attach_adapter调用i2c核心i2c_probe探测设备
static int at24c02_attach_adapter(struct i2c_adapter *adapter)
{
return i2c_probe(adapter, &addr_data, at24c02_detect);
}
static unsigned short normal_i2c[] = { 0x50, 0x51, 0x52, 0x53, 0x54,
0x55, 0x56, 0x57, I2C_CLIENT_END };
/* Insmod parameters */
I2C_CLIENT_INSMOD_1(at24c02);
其中第二个参数add_data是i2c_client_address_data类型的变量，由normal_i2c[]通过宏I2C_CLIENT_INSMOD_1构建而成，具体方法参考i2c.h文件。normal_i2c是i2c芯片的地址，如果地址与芯片对应不上，无法探测到设备，当探测到目标设备后，调用at24c02_detect，把探测到得地址address作为参数传入。
#define AT24C02_MAJOR 250
static int at24c02_major = AT24C02_MAJOR;
struct at24c02_data {
struct cdev cdev;
struct i2c_client client;
struct mutex update_lock;
u8 data[EEPROM_SIZE]; /* Register values */
};
static int at24c02_detect(struct i2c_adapter *adapter, int address, int kind)
{
struct i2c_client *new_client;
struct at24c02_data *data;
int err = 0,result;
dev_t at24c02_dev=MKDEV(at24c02_major,0);
if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_READ_BYTE_DATA
| I2C_FUNC_SMBUS_BYTE)) //判断适配器功能
goto exit;
if (!(data = kzalloc(sizeof(struct at24c02_data), GFP_KERNEL))) {
err = -ENOMEM;
goto exit;
}
new_client = &data->client;
memset(data->data, 0xff, EEPROM_SIZE);
i2c_set_clientdata(new_client, data);
new_client->addr = address;
new_client->adapter = adapter;
new_client->driver = &at24c02_driver;
new_client->flags = 0;
/* Fill in the remaining client fields */
strlcpy(new_client->name, "at24c02", I2C_NAME_SIZE);
mutex_init(&data->update_lock);
/* Tell the I2C layer a new client has arrived */
if ((err = i2c_attach_client(new_client)))
goto exit_kfree;
if(at24c02_major)
{
result=register_chrdev_region(at24c02_dev,1,”at24c02”);
}
else
{
result=alloc_chrdev_region(&at24c02_dev,0,1,”at24c02”);
at24c02_major=MAJOR(at24c02_dev);
}
if(result<0)
{
printk(KERN_NOTICE “Unable to get region %d/n”,result);
err=result;
goto exit_detach;
}
at24c02_setup_cdev(data,0); //注册字符设备at24c02_fops
return 0;
exit_detach:
i2c_detach_client(new_client);
exit_kfree:
kfree(data);
exit:
return err;
}
static void at24c02_setup_cdev(struct at24c02_data *dev,int index)
{
int err,at24c02_dev=MKDEV(at24c02_major,index);
cdev_init(&dev->cdev,&at24c02_fops);
dev_cdev.owner=THIS_MODULE;
err=cdev_add(&dev->cdev,at24c02_dev,1);
if(err)
printk(KERN_NOTICE "error %d adding at24c02 %d/n",err,index);
}
i2c设备驱动卸载函数进行i2c_del_driver调用后，顺序调用内核中注册的适配器断开注册过的i2c设备，此过程是调用at24c02_detach_client实现的。
static void __exit at24c02_exit(void)
{
i2c_del_driver(&at24c02_driver);
}
static int at24c02_detach_client(struct i2c_client *client)
{
int err;
struct at24c02_data *data;
data=i2c_get_client(client);
cdev_del(&(data->cdev));
unregister_chrdev_region(MKDEV(at24c02_major, 0), 1);
err = i2c_detach_client(client);
if (err)
return err;
kfree(data);
return 0;
}
字符驱动的实现
struct file_operations at24c02_fops = {
.owner = THIS_MODULE,
.read= at24c02 _read,
.write= at24c02 _write,
.open= at24c02 _open,
.release = at24c02_release,
};
字符设备驱动不在详述，主要说明如何调用适配器完成数据传输。首先构造消息，通过i2c_transfer来传递，i2c_transfer找到对应适配器algorithm通信方法master_xfer最终完成i2c消息处理。下面是一个关于设备驱动的读函数，其他类似。
static int at24c02_open(struct inode *inode, struct file *file)
{
struct at24c02_data *data;
data=container_of(inode->i_cdev,struct at24c02_data,cdev);
file->private_data = data;
return 0;
}
static int at24c02_read(struct file *filp, char __user *buff,size_t count, loff_t *offp)
{
int ret;
struct i2c_msg msg[2];
char addr = 0;
struct at24c02_data *data=file->private_data;
if (count > 1024)
{
return -EINVAL;
}
msg[0].addr = data->client->addr;
msg[0].flags = 0; /* write */
msg[0].len = 1; /* 1个地址 */
msg[0].buf = &addr;
msg[1].addr = data->client->addr;
msg[1].flags = I2C_M_RD; /* read */
msg[1].len = count; /* 要读的数据个数 */
msg[1].buf = data->data;
ret = i2c_transfer(at24c02_client->adapter, msg, 2);
if (ret == 2)
{
copy_to_user(buff, data->data, count);
return count;
}
else
return -EIO;
}
目前适配器主要支持的传输方法有两种：master_xfer和smbus_xfer，从i2c_algorithm结构体可看出。一般来说，若适配器支持master_xfer那么它可以模拟支持smbus，但只实现smbus_xfer，则不支持master_xfer传输。当然，上面的驱动也可以采用smbus方式完成传输。采用LEGACY方式在2.6.32.2内核下编译不过去，主要是i2c核心中有些函数不存在，所以，设备驱动发展方向是new style方式。
2.new style方式
构建i2c_driver
static struct i2c_driver at24c02_driver = {
.driver = {
.name = "at24c02",
.owner = THIS_MODULE,
},
.probe = at24c02_probe,
.remove = __devexit_p(at24c02_remove),
.id_table = at24c02_id,
};
加载与注销
static int __init at24c02_init(void)
{
return i2c_add_driver(&at24c02_driver);
}
module_init(at24c02_init);
i2c_add_driver会将驱动注册到总线上，探测到i2c设备就会调用at24c02_probe，探测主要是用i2c_match_id函数比较client的名字和id_table中名字，如果相等，则探测到i2c设备，本驱动中id_table如下：
static const struct i2c_device_id at24c02_id[] = {
{ "at24c02", 0 },
{ }
};
MODULE_DEVICE_TABLE(i2c, at24c02_id);
MODULE_DEVICE_TABLE宏是用来生成i2c_device_id。在legacy方式中i2c_client是自己创建的，而此处的i2c_client如何得到？实际上是在i2c_register_board_info函数注册i2c_board_info过程中构建的，所以arch/arm/mach-s3c2440/mach-smdk2440.c中添加注册信息。
static struct i2c_board_info i2c_devices[] __initdata = {
{ I2C_BOARD_INFO("at24c02", 0x50), },
};
static void __init smdk2440_machine_init(void)
{
i2c_register_board_info(0,i2c_devices,ARRAY_SIZE(i2c_devices));
s3c24xx_fb_set_platdata(&smdk2440_fb_info);
s3c_i2c0_set_platdata(NULL);
platform_add_devices(smdk2440_devices, ARRAY_SIZE(smdk2440_devices));
smdk_machine_init();
}
如果没有注册i2c信息，就探测不到i2c设备。探测到at24c02设备后就会调用at24c02_probe函数。
static int __devinit at24c08b_probe(struct i2c_client *client,const struct i2c_device_id *id)
{
struct at24c02_data *data;
int err = 0,result;
dev_t at24c02_dev=MKDEV(at24c02_major,0);
if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_READ_BYTE_DATA
| I2C_FUNC_SMBUS_BYTE)) //判断适配器功能
goto exit;
if (!(data = kzalloc(sizeof(struct at24c02_data), GFP_KERNEL))) {
err = -ENOMEM;
goto exit;
}
memset(data, 0, sizeof(struct at24c02_data));
data->client=client;
i2c_set_clientdata(client, data);
if(at24c02_major)
{
result=register_chrdev_region(at24c02_dev,1,”at24c02”);
}
else
{
result=alloc_chrdev_region(&at24c02_dev,0,1,”at24c02”);
at24c02_major=MAJOR(at24c02_dev);
}
if(result<0)
{
printk(KERN_NOTICE “Unable to get region %d/n”,result);
err=result;
goto exit_kfree;
}
at24c02_setup_cdev(data,0); //注册字符设备at24c02_fops
return 0;
exit_kfree:
kfree(data);
exit:
return err;
}
probe函数主要注册了字符设备，通过data->client=client获得的相关信息。关于at24c02_fops结构体的完善，由于与前面一种方法类似，这里就不详述。最后就是驱动的注销。
static void __exit at24c02_exit(void)
{
i2c_del_driver(&at24c02_driver);
}
module_exit(at24c02_exit);
static int __devexit at24c02_remove(struct i2c_client *client)
{
int err;
struct at24c02_data *data;
data=i2c_get_client(client);
cdev_del(&(data->cdev));
unregister_chrdev_region(MKDEV(at24c02_major, 0), 1);
kfree(data);
return 0;
}
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