Linux驱动子系统之I2C(4)
4 总线驱动
4.1 概述
I2C总线驱动是I2C适配器的软件实现，提供I2C适配器与从设备间完成数据通信的能力，比如起始，停止，应答信号和master_xfer的实现函数。
I2C总线驱动由i2c_adapter和i2c_algorithm来描述
4.2 S3c2440I2C控制器的硬件描述
S3c2440处理器内部集成了一个I2C控制器，通过四个寄存器来进行控制：
IICCON I2C控制寄存器
IICSTAT I2C状态寄存器
IICDS I2C收发数据移位寄存器
IICADD I2C地址寄存器
通过IICCON,IICDS,IICADD寄存器操作，可在I2C总线上产生开始位、停止位、数据和地址，而传输的状态则通过IICSTAT寄存器来获取。
4.3 i2c-s3c2410总线驱动分析(platform_driver)
I2C总线驱动代码在drivers/i2c/busses/i2c-s3c2410.c，这个代码同样支持s3c2410,s3c6410,s5pc110等Samsung 系列的芯片。
初始化模块和卸载模块
- static int __init i2c_adap_s3c_init(void)
- {
- returnplatform_driver_register(&s3c24xx_i2c_driver);
- }
- static void __exit i2c_adap_s3c_exit(void)
- {
- platform_driver_unregister(&s3c24xx_i2c_driver);
- }
static int __init i2c_adap_s3c_init(void)
{
returnplatform_driver_register(&s3c24xx_i2c_driver);
}
static void __exit i2c_adap_s3c_exit(void)
{
platform_driver_unregister(&s3c24xx_i2c_driver);
}
总线驱动是基于platform来实现的，很符合设备驱动模型的思想。
- static struct platform_drivers3c24xx_i2c_driver = {
- .probe = s3c24xx_i2c_probe,
- .remove = s3c24xx_i2c_remove,
- .id_table = s3c24xx_driver_ids,
- .driver = {
- .owner = THIS_MODULE,
- .name = "s3c-i2c",
- .pm = S3C24XX_DEV_PM_OPS,
- .of_match_table= s3c24xx_i2c_match,
- },
- };
static struct platform_drivers3c24xx_i2c_driver = {
.probe = s3c24xx_i2c_probe,
.remove = s3c24xx_i2c_remove,
.id_table = s3c24xx_driver_ids,
.driver = {
.owner = THIS_MODULE,
.name = "s3c-i2c",
.pm = S3C24XX_DEV_PM_OPS,
.of_match_table= s3c24xx_i2c_match,
},
};
s3c24xx_i2c_probe函数
当调用platform_driver_register函数注册platform_driver结构体时，如果platformdevice 和 platform driver匹配成功后，会调用probe函数，来初始化适配器硬件。
- static int s3c24xx_i2c_probe(structplatform_device *pdev)
- {
- ……
- /*初始化适配器信息 */
- strlcpy(i2c->adap.name,"s3c2410-i2c", sizeof(i2c->adap.name));
- i2c->adap.owner = THIS_MODULE;
- i2c->adap.algo = &s3c24xx_i2c_algorithm;
- i2c->adap.retries= 2;
- i2c->adap.class = I2C_CLASS_HWMON | I2C_CLASS_SPD;
- i2c->tx_setup = 50;
- /*初始化自旋锁和等待队列头 */
- spin_lock_init(&i2c->lock);
- init_waitqueue_head(&i2c->wait);
- /*映射寄存器 */
- res= platform_get_resource(pdev, IORESOURCE_MEM, 0);
- i2c->ioarea= request_mem_region(res->start, resource_size(res),
- pdev->name);
- i2c->regs= ioremap(res->start, resource_size(res));
- /*设置I2C核心需要的信息 */
- i2c->adap.algo_data= i2c;
- i2c->adap.dev.parent= &pdev->dev;
- /*初始化I2C控制器 */
- ret= s3c24xx_i2c_init(i2c);
- /*申请中断 */
- i2c->irq= ret = platform_get_irq(pdev, 0);
- ret= request_irq(i2c->irq, s3c24xx_i2c_irq, 0,
- dev_name(&pdev->dev), i2c);
- /* 注册I2C适配器 */
- ret= i2c_add_numbered_adapter(&i2c->adap);
- ……
- }
static int s3c24xx_i2c_probe(structplatform_device *pdev)
{
……
/*初始化适配器信息 */
strlcpy(i2c->adap.name,"s3c2410-i2c", sizeof(i2c->adap.name));
i2c->adap.owner = THIS_MODULE;
i2c->adap.algo = &s3c24xx_i2c_algorithm;
i2c->adap.retries= 2;
i2c->adap.class = I2C_CLASS_HWMON | I2C_CLASS_SPD;
i2c->tx_setup = 50;
/*初始化自旋锁和等待队列头 */
spin_lock_init(&i2c->lock);
init_waitqueue_head(&i2c->wait);
/*映射寄存器 */
res= platform_get_resource(pdev, IORESOURCE_MEM, 0);
i2c->ioarea= request_mem_region(res->start, resource_size(res),
pdev->name);
i2c->regs= ioremap(res->start, resource_size(res));
/*设置I2C核心需要的信息 */
i2c->adap.algo_data= i2c;
i2c->adap.dev.parent= &pdev->dev;
/*初始化I2C控制器 */
ret= s3c24xx_i2c_init(i2c);
/*申请中断 */
i2c->irq= ret = platform_get_irq(pdev, 0);
ret= request_irq(i2c->irq, s3c24xx_i2c_irq, 0,
dev_name(&pdev->dev), i2c);
/* 注册I2C适配器 */
ret= i2c_add_numbered_adapter(&i2c->adap);
……
}
Probe主要工作是时能硬件并申请I2C适配器使用的IO地址，中断号等，然后向I2C核心添加这个适配器。I2c_adapter注册过程i2c_add_numbered_adapter->i2c_register_adapter
I2C总线通信方法
- static const struct i2c_algorithms3c24xx_i2c_algorithm = {
- .master_xfer = s3c24xx_i2c_xfer,
- .functionality = s3c24xx_i2c_func,
- };
static const struct i2c_algorithms3c24xx_i2c_algorithm = {
.master_xfer = s3c24xx_i2c_xfer,
.functionality = s3c24xx_i2c_func,
};
s3c24xx_i2c_xfer函数是总线通信方式的具体实现，依赖于s3c24xx_i2c_doxfer和s3c24xx_i2c_message_start两个函数；
- static int s3c24xx_i2c_doxfer(structs3c24xx_i2c *i2c,
- struct i2c_msg *msgs, int num)
- {
- ret =s3c24xx_i2c_set_master(i2c);
- i2c->msg = msgs;
- i2c->msg_num= num;
- i2c->msg_ptr= 0;
- i2c->msg_idx= 0;
- i2c->state = STATE_START;
- s3c24xx_i2c_message_start(i2c,msgs);
- }
static int s3c24xx_i2c_doxfer(structs3c24xx_i2c *i2c,
struct i2c_msg *msgs, int num)
{
ret =s3c24xx_i2c_set_master(i2c);
i2c->msg = msgs;
i2c->msg_num= num;
i2c->msg_ptr= 0;
i2c->msg_idx= 0;
i2c->state = STATE_START;
s3c24xx_i2c_message_start(i2c,msgs);
}
首先设置s3c I2C设备器为主设备，然后调用s3c24xx_i2c_message_start函数启动I2C消息传输。
s3c24xx_i2c_func函数返回适配器所支持的通信功能。
4.4 适配器的设备资源(platform_device)
S3c2440的I2C总线驱动是基于platform来实现，前面我们分析了platformdriver部分，再来看下platform device部分。
在arch/arm/plat-samsung/dev-i2c0.c文件中定义了platform_device结构体以及I2C控制器的资源信息：
- 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", /* 设备名 */
- #ifdef CONFIG_S3C_DEV_I2C1
- .id = 0,
- #else
- .id = -1,
- #endif
- .num_resources =ARRAY_SIZE(s3c_i2c_resource),
- .resource =s3c_i2c_resource,
- };
- struct s3c2410_platform_i2cdefault_i2c_data __initdata = {
- .flags = 0,
- .slave_addr = 0x10, /* I2C适配器的地址 */
- .frequency = 100*1000, /* 总线频率 */
- .sda_delay = 100, /* SDA边沿延迟时间ns */
- };
- void __init s3c_i2c0_set_platdata(structs3c2410_platform_i2c *pd)
- {
- structs3c2410_platform_i2c *npd;
- if(!pd)
- pd= &default_i2c_data;
- npd= s3c_set_platdata(pd, sizeof(struct s3c2410_platform_i2c),
- &s3c_device_i2c0);
- if(!npd->cfg_gpio)
- npd->cfg_gpio= s3c_i2c0_cfg_gpio;
- }
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", /* 设备名 */
#ifdef CONFIG_S3C_DEV_I2C1
.id = 0,
#else
.id = -1,
#endif
.num_resources =ARRAY_SIZE(s3c_i2c_resource),
.resource =s3c_i2c_resource,
};
struct s3c2410_platform_i2cdefault_i2c_data __initdata = {
.flags = 0,
.slave_addr = 0x10, /* I2C适配器的地址 */
.frequency = 100*1000, /* 总线频率 */
.sda_delay = 100, /* SDA边沿延迟时间ns */
};
void __init s3c_i2c0_set_platdata(structs3c2410_platform_i2c *pd)
{
structs3c2410_platform_i2c *npd;
if(!pd)
pd= &default_i2c_data;
npd= s3c_set_platdata(pd, sizeof(struct s3c2410_platform_i2c),
&s3c_device_i2c0);
if(!npd->cfg_gpio)
npd->cfg_gpio= s3c_i2c0_cfg_gpio;
}
在板文件中把platform_device注册进内核：
- static struct platform_device*mini2440_devices[] __initdata = {
- ……
- &s3c_device_i2c0,
- ……
- };
static struct platform_device*mini2440_devices[] __initdata = {
……
&s3c_device_i2c0,
……
};
调用s3c_i2c0_set_platdata 函数把适配器具体的数据赋值给dev.platform_data：
- static void __init mini2440_init(void)
- {
- ……
- s3c_i2c0_set_platdata(NULL);
- }
static void __init mini2440_init(void)
{
……
s3c_i2c0_set_platdata(NULL);
}
I2C总线驱动就分析到这里。