在这一节将会介绍S3C2440 I2C适配器的注册，以及AT24C08、SSD1606 OLED I2C设备驱动的编写。
一、I2C适配器注册
在Mini2440裸机开发之I2C（AT24C08）我们介绍了S3C2440这款SOC的I2C结构，其内部只有一个I2C控制器，其中SCL连接GPE14引脚，SDA连接GPE15引脚。
1.1 platform设备注册(s3c2410-i2c)
1.1.1 s3c_device_i2c0
向往常一样，我们依然是定位到arch/arm/mach-s3c24xx/mach-smdk2440.c文件，在该文我们可以找到platform设备s3c_device_i2c0变量，其定义在arch/arm/plat-samsung/devs.c文件：
/* I2C */
static struct resource s3c_i2c0_resource[] = {
[0] = DEFINE_RES_MEM(S3C_PA_IIC, SZ_4K),
[1] = DEFINE_RES_IRQ(IRQ_IIC),
};
struct platform_device s3c_device_i2c0 = { // platform设备信息
.name = "s3c2410-i2c",
.id = 0,
.num_resources = ARRAY_SIZE(s3c_i2c0_resource),
.resource = s3c_i2c0_resource,
};
struct s3c2410_platform_i2c default_i2c_data __initdata = { // 用于初始化&s3c_device_i2c0->dev.platform_data
.flags = 0,
.slave_addr = 0x10, // 从设备地址
.frequency = 100*1000, // 频率 100kb
.sda_delay = 100,
};
void __init s3c_i2c0_set_platdata(struct s3c2410_platform_i2c *pd) // 用于绑定s3c_device_i2c0->dev.platform_data和default_i2c_data的关系
{
struct s3c2410_platform_i2c *npd;
if (!pd) {
pd = &default_i2c_data;
pd->bus_num = 0;
}
npd = s3c_set_platdata(pd, sizeof(*npd), &s3c_device_i2c0); // &s3c_device_i2c0->dev.platform_data = default_i2c_data
if (!npd->cfg_gpio)：
npd->cfg_gpio = s3c_i2c0_cfg_gpio;
}
我们重点关注一下platform设备资源定义，这里定义了2个资源，第1个是内存资源、第2个是中断资源：
- 第一个资源是IO内存资源，起始地址是I2C寄存器寄基地址，即0x54000000，大小位4Kb；
- 第二个资源必须是中断资源，中断号位IRQ_IIC，即27；
我们已经定义了I2C控制器相关的platform_device设备s3c_device_i2c0，并进行了初始化，那platform设备啥时候注册的呢？
linux内核启动的时候会根据uboot中设置的机器id执行相应的初始化工作，比如.init_machine、.init_irq，我们首先定位到arch/arm/mach-s3c24xx/mach-smdk2440.c：
MACHINE_START(S3C2440, "SMDK2440")
/* Maintainer: Ben Dooks <[email protected]> */
.atag_offset = 0x100,
.init_irq = s3c2440_init_irq,
.map_io = smdk2440_map_io,
.init_machine = smdk2440_machine_init,
.init_time = smdk2440_init_time,
MACHINE_END
重点关注init_machine，init_machine中保存的是开发板资源注册的初始化代码。
1.1.2 smdk2440_machine_init
static void __init smdk2440_machine_init(void)
{
s3c24xx_fb_set_platdata(&smdk2440_fb_info);
s3c_i2c0_set_platdata(NULL); // 初始化s3c_device_i2c0->dev.platform_data
platform_add_devices(smdk2440_devices, ARRAY_SIZE(smdk2440_devices)); // s3c2440若干个platform设备注册 usb host controller、lcd、wdt等
smdk_machine_init(); // s3c24x0系列若干个platform设备注册（通用）
}
这里利用platform_add_devices进行若干个platform设备的注册，该函数通过调用platform_device_register实现platform设备注册。
static struct platform_device *smdk2440_devices[] __initdata = {
&s3c_device_ohci,
&s3c_device_lcd,
&s3c_device_wdt,
&s3c_device_i2c0,
&s3c_device_iis,
&smdk2440_device_eth,
};
1.2 platform驱动注册(s3c2410-i2c)
I2C控制器platform驱动定义位于drivers/i2c/busses/i2c-s3c2410.c文件中。
1.2.1 入口和出口函数
我们在i2c-s3c2410.c文件定位到驱动模块的入口和出口：
static struct platform_driver s3c24xx_i2c_driver = {
.probe = s3c24xx_i2c_probe,
.remove = s3c24xx_i2c_remove,
.id_table = s3c24xx_driver_ids,
.driver = {
.name = "s3c-i2c",
.pm = S3C24XX_DEV_PM_OPS,
.of_match_table = of_match_ptr(s3c24xx_i2c_match),
},
};
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);
在plaftrom总线设备驱动模型中，我们知道当内核中有platform设备platform驱动匹配，会调用到platform_driver里的成员.probe，在这里就是s3c24xx_i2c_probe函数。
1.2.2 I2C相关数据结构
在介绍s3c24xx_i2c_probe之前，先来看一下s3c24xx_i2c结构体定义：
struct s3c24xx_i2c { // 用来表示SOC的一个I2C控制器
wait_queue_head_t wait; // 等待队列
kernel_ulong_t quirks;
struct i2c_msg *msg; // 存放要发送的I2C数据包
unsigned int msg_num; // 数据包个数 实际只有1个
unsigned int msg_idx; // 当前发送的数据包索引
unsigned int msg_ptr; // 当前传输的字节在数据包的索引
unsigned int tx_setup; // 用来延时，等待SCL被释放
unsigned int irq; // 中断号
enum s3c24xx_i2c_state state; // I2C传输状态 STATE_START、STATE_IDEL、STATE_STOP、STATE_WRITE、STATE_READ
unsigned long clkrate;
void __iomem *regs;
struct clk *clk; // 时钟
struct device *dev; // 存储platform设备的dev成员
struct i2c_adapter adap; // 描述该I2C控制器的适配器
struct s3c2410_platform_i2c *pdata; // 私有数据 默认初始化为&default_i2c_data
int gpios[2];
struct pinctrl *pctrl;
#if defined(CONFIG_ARM_S3C24XX_CPUFREQ)
struct notifier_block freq_transition;
#endif
struct regmap *sysreg;
unsigned int sys_i2c_cfg;
};
s3c2410_platform_i2c定义在include/linux/platform_data/i2c-s3c2410.h文件：
/**
* struct s3c2410_platform_i2c - Platform data for s3c I2C.
* @bus_num: The bus number to use (if possible).
* @flags: Any flags for the I2C bus (E.g. S3C_IICFLK_FILTER).
* @slave_addr: The I2C address for the slave device (if enabled).
* @frequency: The desired frequency in Hz of the bus. This is
* guaranteed to not be exceeded. If the caller does
* not care, use zero and the driver will select a
* useful default.
* @sda_delay: The delay (in ns) applied to SDA edges.
* @cfg_gpio: A callback to configure the pins for I2C operation.
*/
struct s3c2410_platform_i2c {
int bus_num;
unsigned int flags;
unsigned int slave_addr;
unsigned long frequency;
unsigned int sda_delay;
void (*cfg_gpio)(struct platform_device *dev); // 配置gpio口
};
1.2.3 s3c24xx_i2c_probe
static int s3c24xx_i2c_probe(struct platform_device *pdev)
{
struct s3c24xx_i2c *i2c;
struct s3c2410_platform_i2c *pdata = NULL;
struct resource *res;
int ret;
if (!pdev->dev.of_node) {
pdata = dev_get_platdata(&pdev->dev); // &pdev->dev.platform_data即default_i2c_data
if (!pdata) {
dev_err(&pdev->dev, "no platform data\n");
return -EINVAL;
}
}
i2c = devm_kzalloc(&pdev->dev, sizeof(struct s3c24xx_i2c), GFP_KERNEL); // 为i2c动态申请内存，&pdev->dev卸载时释放
if (!i2c)
return -ENOMEM;
i2c->pdata = devm_kzalloc(&pdev->dev, sizeof(*pdata), GFP_KERNEL); // 为i2c->pdata动态申请内存，&pdev->dev卸载时释放
if (!i2c->pdata)
return -ENOMEM;
i2c->quirks = s3c24xx_get_device_quirks(pdev);
i2c->sysreg = ERR_PTR(-ENOENT);
if (pdata)
memcpy(i2c->pdata, pdata, sizeof(*pdata)); // 走这里，初始化i2c->pdata
else
s3c24xx_i2c_parse_dt(pdev->dev.of_node, i2c); // 解析设备树
strlcpy(i2c->adap.name, "s3c2410-i2c", sizeof(i2c->adap.name)); // 设置I2C适配器名称
i2c->adap.owner = THIS_MODULE;
i2c->adap.algo = &s3c24xx_i2c_algorithm; // 设置I2C适配器通信算法
i2c->adap.retries = 2; // 重试次数
i2c->adap.class = I2C_CLASS_DEPRECATED; // 设置成这个？？是是有问题 I2C_CLASS_HWMON
i2c->tx_setup = 50;
init_waitqueue_head(&i2c->wait); // 初始化等待队列
/* find the clock and enable it */
i2c->dev = &pdev->dev;
i2c->clk = devm_clk_get(&pdev->dev, "i2c"); // 获取i2c时钟
if (IS_ERR(i2c->clk)) {
dev_err(&pdev->dev, "cannot get clock\n");
return -ENOENT;
}
dev_dbg(&pdev->dev, "clock source %p\n", i2c->clk);
/* map the registers */
res = platform_get_resource(pdev, IORESOURCE_MEM, 0); // 获取第一个IO内存资源
i2c->regs = devm_ioremap_resource(&pdev->dev, res); // 物理地址->虚拟地址映射 映射是I2C控制器寄存器地址
if (IS_ERR(i2c->regs))
return PTR_ERR(i2c->regs);
dev_dbg(&pdev->dev, "registers %p (%p)\n",
i2c->regs, res);
/* setup info block for the i2c core */
i2c->adap.algo_data = i2c; // 私有数据指向i2c
i2c->adap.dev.parent = &pdev->dev; // 设置I2C适配器dev.parent为&pdev->dev
i2c->pctrl = devm_pinctrl_get_select_default(i2c->dev);
/* inititalise the i2c gpio lines */
if (i2c->pdata->cfg_gpio) // 配置gpio
i2c->pdata->cfg_gpio(to_platform_device(i2c->dev));
else if (IS_ERR(i2c->pctrl) && s3c24xx_i2c_parse_dt_gpio(i2c))
return -EINVAL;
/* initialise the i2c controller */
ret = clk_prepare_enable(i2c->clk); // 使能时钟 CLKCON寄存器的bit[66]对应着I2C模块
if (ret) {
dev_err(&pdev->dev, "I2C clock enable failed\n");
return ret;
}
ret = s3c24xx_i2c_init(i2c); // 初始化I2C相关的寄存器
clk_disable(i2c->clk); // 禁止时钟
if (ret != 0) {
dev_err(&pdev->dev, "I2C controller init failed\n");
clk_unprepare(i2c->clk);
return ret;
}
/*
* find the IRQ for this unit (note, this relies on the init call to
* ensure no current IRQs pending
*/
if (!(i2c->quirks & QUIRK_POLL)) {
i2c->irq = ret = platform_get_irq(pdev, 0); // 获取中断资源
if (ret <= 0) {
dev_err(&pdev->dev, "cannot find IRQ\n");
clk_unprepare(i2c->clk);
return ret;
}
ret = devm_request_irq(&pdev->dev, i2c->irq, s3c24xx_i2c_irq, // 注册中断服务
0, dev_name(&pdev->dev), i2c);
if (ret != 0) {
dev_err(&pdev->dev, "cannot claim IRQ %d\n", i2c->irq);
clk_unprepare(i2c->clk);
return ret;
}
}
ret = s3c24xx_i2c_register_cpufreq(i2c);
if (ret < 0) {
dev_err(&pdev->dev, "failed to register cpufreq notifier\n");
clk_unprepare(i2c->clk);
return ret;
}
/*
* 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 = i2c->pdata->bus_num; // 设置I2C适配器编号
i2c->adap.dev.of_node = pdev->dev.of_node;
platform_set_drvdata(pdev, i2c); // 设置pdev.dev.plat_data = i2c
pm_runtime_enable(&pdev->dev);
ret = i2c_add_numbered_adapter(&i2c->adap); // 注册I2C适配器
if (ret < 0) {
pm_runtime_disable(&pdev->dev);
s3c24xx_i2c_deregister_cpufreq(i2c);
clk_unprepare(i2c->clk);
return ret;
}
dev_info(&pdev->dev, "%s: S3C I2C adapter\n", dev_name(&i2c->adap.dev));
return 0;
}
这段代码属实有点长了，让人一眼看过去，就有点想放弃去读的想法，既然都学习到了这一步，我们还是耐着性去分析吧。这里代码理解起来还是比较简单的，主要流程如下：
- 设置i2c_adapter适配器结构体；
- 设置name为s3c2410-i2c；
- 设置algo为s3c24xx_i2c_algorithm；
- 设置retries为2；
- 设置algo_data 为i2c；
- 设置dev.parent为&pdev->dev；
- 设置nr为i2c->pdata->bus_num;
- ...
- 调用s3c24xx_i2c_init初始化S3C2440 I2C相关的寄存器；
- 调用devm_request_irq注册I2C中断，中断处理服务函数为s3c24xx_i2c_irq；
- 调用i2c_add_numbered_adapter注册i2c_adapter适配器结构体；
1.2.4 s3c24xx_i2c_algorithm
/* i2c bus registration info */
static const struct i2c_algorithm s3c24xx_i2c_algorithm = {
.master_xfer = s3c24xx_i2c_xfer, /* 数据传输，这个上一节已经介绍了 */
.functionality = s3c24xx_i2c_func,
};
s3c24xx_i2c_xfer函数在u上一节已经介绍了，与SOC的I2C控制器寄存器设置相关了，基本是裸机相关的内容，无非就是产生 I2C 通信时序，如开始信号，停止信号、应答信号等。
1.2.5 s3c24xx_i2c_init
s3c24xx_i2c_init函数主要就是进行I2C控制器的初始化工作：
/*
* initialise the controller, set the IO lines and frequency
*/
static int s3c24xx_i2c_init(struct s3c24xx_i2c *i2c)
{
struct s3c2410_platform_i2c *pdata;
unsigned int freq;
/* get the plafrom data */
pdata = i2c->pdata;
/* write slave address */
writeb(pdata->slave_addr, i2c->regs + S3C2410_IICADD); // 写入从设备地址
dev_info(i2c->dev, "slave address 0x%02x\n", pdata->slave_addr);
writel(0, i2c->regs + S3C2410_IICCON); // 初始化IICCON=0
writel(0, i2c->regs + S3C2410_IICSTAT); // 初始化IICSTAT=0
/* we need to work out the divisors for the clock... */
if (s3c24xx_i2c_clockrate(i2c, &freq) != 0) { // 这个函数主要就是根据当前i2c时钟频率以及预设的I2C控制器目标频率，计算IIC总线发送时钟预分频系数，freq为设置的实际频率
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%02x\n",
readl(i2c->regs + S3C2410_IICCON));
return 0;
}
1.2.6 s3c24xx_i2c_irq
s3c24xx_i2c_irq调用下一个字节传输函数i2s_s3c_irq_nextbyte()来传输数据。
/*
* top level IRQ servicing routine
*/
static irqreturn_t s3c24xx_i2c_irq(int irqno, void *dev_id)
{
struct s3c24xx_i2c *i2c = dev_id;
unsigned long status;
unsigned long tmp;
status = readl(i2c->regs + S3C2410_IICSTAT);
if (status & S3C2410_IICSTAT_ARBITR) { // 仲裁失败
/* deal with arbitration loss */
dev_err(i2c->dev, "deal with arbitration loss\n");
}
if (i2c->state == STATE_IDLE) { // 空闲状态
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); // 清I2C中断挂起 IICCON位[4]
goto out;
}
/*
* pretty much this leaves us with the fact that we've
* transmitted or received whatever byte we last sent
*/
i2c_s3c_irq_nextbyte(i2c, status); // 继续数据传输
out:
return IRQ_HANDLED;
}
二、AT24C08设备驱动注册
标签：I2C,s3c24xx,dev,platform,OLED,pdev,驱动,i2c,移植 From： https://www.cnblogs.com/zyly/p/17133091.html