Kernel的IIC驅動分析
涉及到的文件：
drivers/i2c/i2c-core.c
drivers/i2c/i2c-dev.c
drivers/i2c/busses/i2c-imx.c
等等
在下面分析的代碼中，不想關或者不重要的，我會省略掉。
1. 適配器設備的註冊
在Linux內核啟動的過程中，會調用到mx6_sabresd_board_init函數
static void __init mx6_sabresd_board_init(void)
{
。。。省略。。。
/*在這裏修改了i2c0適配器上設備的類型，同時添加了平臺數據，後面會分析到*/
strcpy(mxc_i2c0_board_info[0].type,
mxc_i2c0_board_info[0].platform_data = &wm8962_config_data;
/*第一步：註冊適配器設備：詳見下面分析*/
imx6q_add_imx_i2c(0, &mx6q_sabresd_i2c_data);
/*第二步：添加I2C從設備*/
i2c_register_board_info(0, mxc_i2c0_board_info,
ARRAY_SIZE(mxc_i2c0_board_info));
。。。省略。。。
}
下面我們來分析第一步：註冊適配器設備
extern const struct imx_imx_i2c_data imx6q_imx_i2c_data[] __initconst;
#define imx6q_add_imx_i2c(id, pdata) \
imx_add_imx_i2c(&imx6q_imx_i2c_data[id], pdata)
接著追到imx_add_imx_i2c，我們可以知道
1). 通過imx_add_platform_device ，我們知道I2C的適配器設備是放入了平臺總線模型當中，並且名字為imx-i2c。
2). 第一個參數imx_imx_i2c_data是適配器的設備信息，包括I2C寄存器地址，中斷號，資源res是通過data的重新賦值。它包括了I2C寄存器的基地址，中斷號，總線編號。第二個參數imxi2c_platform_data是存放在平臺上的數據，下面我們來分析這兩個參數。
struct platform_device *__init imx_add_imx_i2c(
const struct imx_imx_i2c_data *data,
const struct imxi2c_platform_data *pdata)
{
struct resource res[] = {
{
.start = data->iobase,
.end = data->iobase + data->iosize - 1,
.flags = IORESOURCE_MEM,
}, {
.start = data->irq,
.end = data->irq,
.flags = IORESOURCE_IRQ,
},
};
return imx_add_platform_device("imx-i2c", data->id,
res, ARRAY_SIZE(res),
pdata, sizeof(*pdata));
}
我們先分析第一個參數imx_add_platform_device：
我們往回查看上述函數的關鍵數據
imx_imx_i2c_data* data= imx6q_imx_i2c_data[0]
const struct imx_imx_i2c_data imx6q_imx_i2c_data[] __initconst = {
#define imx6q_imx_i2c_data_entry(_id, _hwid) \
imx_imx_i2c_data_entry(MX6Q, _id, _hwid, SZ_4K)
imx6q_imx_i2c_data_entry(0, 1),
imx6q_imx_i2c_data_entry(1, 2),
imx6q_imx_i2c_data_entry(2, 3),
};
接著追imx_imx_i2c_data_entry
#define imx_imx_i2c_data_entry(soc, _id, _hwid, _size) \
[_id] = imx_imx_i2c_data_entry_single(soc, _id, _hwid, _size)
再接著追imx_imx_i2c_data_entry
#define imx_imx_i2c_data_entry_single(soc, _id, _hwid, _size) \
{ \
.id = _id, \
.iobase = soc ## _I2C ## _hwid ## _BASE_ADDR, \
.iosize = _size, \
.irq = soc ## _INT_I2C ## _hwid, \
}
通過一層層的代入展開，可以推導出：
imx6q_imx_i2c_data[0]=
{
.id = 0,
.iobase = MX6Q_I2C1_BASE_ADDR,
.iosize = _SZ_4K,
.irq = MX6Q_INT_I2C1,
}
第二個參數mx6q_sabresd_i2c_data是時鐘系數：
static struct imxi2c_platform_data mx6q_sabresd_i2c_data = {
.bitrate = 100000,
};
2. 適配器驅動的流程
從之前的代碼，我們得知適配器設備在平臺驅動模型中的名字為imx-i2c。
其代碼在drivers/i2c/busses/i2c-imx.c
static struct platform_driver i2c_imx_driver = {
.remove = __exit_p(i2c_imx_remove),
.driver = {
.name = DRIVER_NAME, /*imx-i2c*/
.owner = THIS_MODULE,
}
};
/*通過平臺模型註冊*/
static int __init i2c_adap_imx_init(void)
{
return platform_driver_probe(&i2c_imx_driver, i2c_imx_probe);
}
當名字imx-i2c匹配上的時候，會自動調用探測函數i2c_imx_probe，其原理屬於平臺驅動模型。在這裏面會對I2C進行初始化：設置始終，初始化I2C寄存器，設置中斷等。
static int __init i2c_imx_probe(struct platform_device *pdev)
{
struct imx_i2c_struct *i2c_imx;
struct resource *res;
struct imxi2c_platform_data *pdata;
void __iomem *base;
resource_size_t res_size;
int irq;
int ret;
dev_dbg(&pdev->dev, "<%s>\n", __func__);
/*獲取來自適配器設備上的內存資源：I2C寄存器地址*/
res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
if (!res) {
dev_err(&pdev->dev, "can‘t get device resources\n");
return -ENOENT;
}
/*獲取來自適配器設備上的中斷號*/
irq = platform_get_irq(pdev, 0);
if (irq < 0) {
dev_err(&pdev->dev, "can‘t get irq number\n");
return -ENOENT;
}
/*獲取平臺數據：也就是之前分析的時鐘系數*/
pdata = pdev->dev.platform_data;
if (pdata && pdata->init) {
ret = pdata->init(&pdev->dev);
if (ret)
return ret;
}
res_size = resource_size(res);
/*將寄存器地址映射為虛擬內存*/
if (!request_mem_region(res->start, res_size, DRIVER_NAME)) {
ret = -EBUSY;
goto fail0;
}
base = ioremap(res->start, res_size);
if (!base) {
dev_err(&pdev->dev, "ioremap failed\n");
ret = -EIO;
goto fail1;
}
i2c_imx = kzalloc(sizeof(struct imx_i2c_struct), GFP_KERNEL);
if (!i2c_imx) {
dev_err(&pdev->dev, "can‘t allocate interface\n");
ret = -ENOMEM;
goto fail2;
}
/* Setup i2c_imx driver structure */
strcpy(i2c_imx->adapter.name, pdev->name);
i2c_imx->adapter.owner = THIS_MODULE;
i2c_imx->adapter.algo = &i2c_imx_algo; /*算法層：這個是跟具體硬件和協議相關的，下面分析*/
i2c_imx->adapter.dev.parent = &pdev->dev;
i2c_imx->adapter.nr = pdev->id; /*名字*/
i2c_imx->irq = irq;
i2c_imx->base = base;
i2c_imx->res = res;
/* 設置I2C時鐘 */
i2c_imx->clk = clk_get(&pdev->dev, "i2c_clk");
if (IS_ERR(i2c_imx->clk)) {
ret = PTR_ERR(i2c_imx->clk);
dev_err(&pdev->dev, "can‘t get I2C clock\n");
goto fail3;
}
/* 設置中斷 */
ret = request_irq(i2c_imx->irq, i2c_imx_isr, 0, pdev->name, i2c_imx);
if (ret) {
dev_err(&pdev->dev, "can‘t claim irq %d\n", i2c_imx->irq);
goto fail4;
}
/* 等待隊列 */
init_waitqueue_head(&i2c_imx->queue);
/* 設置適配器數據 */
i2c_set_adapdata(&i2c_imx->adapter, i2c_imx);
/* 設置時鐘分頻 */
if (pdata && pdata->bitrate)
i2c_imx_set_clk(i2c_imx, pdata->bitrate);
else
i2c_imx_set_clk(i2c_imx, IMX_I2C_BIT_RATE);
/* 設置I2C的寄存器 */
writeb(0, i2c_imx->base + IMX_I2C_I2CR);
writeb(0, i2c_imx->base + IMX_I2C_I2SR);
/* 註冊適配器驅動：這個我們後面會分析 */
ret = i2c_add_numbered_adapter(&i2c_imx->adapter);
if (ret < 0) {
dev_err(&pdev->dev, "registration failed\n");
goto fail5;
}
/* 將i2c_imx數據放入平臺總線中 */
platform_set_drvdata(pdev, i2c_imx);
dev_dbg(&i2c_imx->adapter.dev, "claimed irq %d\n", i2c_imx->irq);
dev_dbg(&i2c_imx->adapter.dev, "device resources from 0x%x to 0x%x\n",
i2c_imx->res->start, i2c_imx->res->end);
dev_dbg(&i2c_imx->adapter.dev, "allocated %d bytes at 0x%x \n",
res_size, i2c_imx->res->start);
dev_dbg(&i2c_imx->adapter.dev, "adapter name: \"%s\"\n",
i2c_imx->adapter.name);
dev_dbg(&i2c_imx->adapter.dev, "IMX I2C adapter registered\n");
return 0; /* Return OK */
fail5:
free_irq(i2c_imx->irq, i2c_imx);
fail4:
clk_put(i2c_imx->clk);
fail3:
kfree(i2c_imx);
fail2:
iounmap(base);
fail1:
release_mem_region(res->start, resource_size(res));
fail0:
if (pdata && pdata->exit)
pdata->exit(&pdev->dev);
return ret; /* Return error number */
}
/*這個函數的主要功能是提供該適配器能提供的I2C功能，提供判斷*/
static u32 i2c_imx_func(struct i2c_adapter *adapter)
{
return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL;
}
static struct i2c_algorithm i2c_imx_algo = {
.master_xfer = i2c_imx_xfer, /*具體的傳輸的實現*/
.functionality = i2c_imx_func, /*傳輸的方式*/
};
static int i2c_imx_xfer(struct i2c_adapter *adapter,
struct i2c_msg *msgs, int num)
{
unsigned int i, temp;
int result;
/*將該適配器上的數據取出來*/
struct imx_i2c_struct *i2c_imx = i2c_get_adapdata(adapter);
dev_dbg(&i2c_imx->adapter.dev, "<%s>\n", __func__);
/* I2C起始位 */
result = i2c_imx_start(i2c_imx);
if (result)
goto fail0;
/* 對數據進行讀寫 */
for (i = 0; i < num; i++) {
if (i) {
dev_dbg(&i2c_imx->adapter.dev,
"<%s> repeated start\n", __func__);
temp = readb(i2c_imx->base + IMX_I2C_I2CR);
temp |= I2CR_RSTA;
writeb(temp, i2c_imx->base + IMX_I2C_I2CR);
result = i2c_imx_bus_busy(i2c_imx, 1);
if (result)
goto fail0;
}
dev_dbg(&i2c_imx->adapter.dev,
"<%s> transfer message: %d\n", __func__, i);
/* write/read data */
#ifdef CONFIG_I2C_DEBUG_BUS
temp = readb(i2c_imx->base + IMX_I2C_I2CR);
dev_dbg(&i2c_imx->adapter.dev, "<%s> CONTROL: IEN=%d, IIEN=%d, "
"MSTA=%d, MTX=%d, TXAK=%d, RSTA=%d\n", __func__,
(temp & I2CR_IEN ? 1 : 0), (temp & I2CR_IIEN ? 1 : 0),
(temp & I2CR_MSTA ? 1 : 0), (temp & I2CR_MTX ? 1 : 0),
(temp & I2CR_TXAK ? 1 : 0), (temp & I2CR_RSTA ? 1 : 0));
temp = readb(i2c_imx->base + IMX_I2C_I2SR);
dev_dbg(&i2c_imx->adapter.dev,
"<%s> STATUS: ICF=%d, IAAS=%d, IBB=%d, "
"IAL=%d, SRW=%d, IIF=%d, RXAK=%d\n", __func__,
(temp & I2SR_ICF ? 1 : 0), (temp & I2SR_IAAS ? 1 : 0),
(temp & I2SR_IBB ? 1 : 0), (temp & I2SR_IAL ? 1 : 0),
(temp & I2SR_SRW ? 1 : 0), (temp & I2SR_IIF ? 1 : 0),
(temp & I2SR_RXAK ? 1 : 0));
#endif
if (msgs[i].flags & I2C_M_RD)
result = i2c_imx_read(i2c_imx, &msgs[i]);
else
result = i2c_imx_write(i2c_imx, &msgs[i]);
if (result)
goto fail0;
}
fail0:
/* 停止位 */
i2c_imx_stop(i2c_imx);
dev_dbg(&i2c_imx->adapter.dev, "<%s> exit with: %s: %d\n", __func__,
(result < 0) ? "error" : "success msg",
(result < 0) ? result : num);
return (result < 0) ? result : num;
}
這個函數裏面得到所有函數就是最底層真正對硬件的操作了，比如：
static int i2c_imx_start(struct imx_i2c_struct *i2c_imx)
{
unsigned int temp = 0;
struct imxi2c_platform_data *pdata;
int result;
dev_dbg(&i2c_imx->adapter.dev, "<%s>\n", __func__);
/* Currently on Arik/Rigel, the I2C clk is from IPG_PERCLK which is
* sourced from IPG_CLK. In low bus freq mode, IPG_CLK is at 12MHz
* and IPG_PERCLK is down to 4MHz.
* Update I2C divider before set i2c clock.
*/
pdata = i2c_imx->adapter.dev.parent->platform_data;
if (pdata && pdata->bitrate)
i2c_imx_set_clk(i2c_imx, pdata->bitrate);
else
i2c_imx_set_clk(i2c_imx, IMX_I2C_BIT_RATE);
clk_enable(i2c_imx->clk);
writeb(i2c_imx->ifdr, i2c_imx->base + IMX_I2C_IFDR);
/* Enable I2C controller */
writeb(0, i2c_imx->base + IMX_I2C_I2SR);
writeb(I2CR_IEN, i2c_imx->base + IMX_I2C_I2CR);
/* Wait controller to be stable */
udelay(50);
/* Start I2C transaction */
temp = readb(i2c_imx->base + IMX_I2C_I2CR);
temp |= I2CR_MSTA;
writeb(temp, i2c_imx->base + IMX_I2C_I2CR);
result = i2c_imx_bus_busy(i2c_imx, 1);
if (result)
return result;
i2c_imx->stopped = 0;
temp |= I2CR_IIEN | I2CR_MTX | I2CR_TXAK;
writeb(temp, i2c_imx->base + IMX_I2C_I2CR);
return result;
}
在i2c_add_numbered_adapter中會對最後的適配器驅動進行註冊，在註冊之前還會對I2C設備驅動進行註冊。
int i2c_add_numbered_adapter(struct i2c_adapter *adap)
{
int id;
int status;
if (adap->nr & ~MAX_ID_MASK)
return -EINVAL;
retry:
if (idr_pre_get(&i2c_adapter_idr, GFP_KERNEL) == 0)
return -ENOMEM;
mutex_lock(&core_lock);
/* "above" here means "above or equal to", sigh;
* we need the "equal to" result to force the result
*/
status = idr_get_new_above(&i2c_adapter_idr, adap, adap->nr, &id);
if (status == 0 && id != adap->nr) {
status = -EBUSY;
idr_remove(&i2c_adapter_idr, id);
}
mutex_unlock(&core_lock);
if (status == -EAGAIN)
goto retry;
if (status == 0)
/*在這裏真正註冊I2C適配器*/
status = i2c_register_adapter(adap);
return status;
}
static int i2c_register_adapter(struct i2c_adapter *adap)
{
int res = 0;
/* Can‘t register until after driver model init */
if (unlikely(WARN_ON(!i2c_bus_type.p))) {
res = -EAGAIN;
goto out_list;
}
/* Sanity checks */
if (unlikely(adap->name[0] == ‘\0‘)) {
pr_err("i2c-core: Attempt to register an adapter with "
"no name!\n");
return -EINVAL;
}
if (unlikely(!adap->algo)) {
pr_err("i2c-core: Attempt to register adapter ‘%s‘ with "
"no algo!\n", adap->name);
return -EINVAL;
}
rt_mutex_init(&adap->bus_lock);
mutex_init(&adap->userspace_clients_lock);
INIT_LIST_HEAD(&adap->userspace_clients);
/* Set default timeout to 1 second if not already set */
if (adap->timeout == 0)
adap->timeout = HZ;
dev_set_name(&adap->dev, "i2c-%d", adap->nr);
adap->dev.bus = &i2c_bus_type;
adap->dev.type = &i2c_adapter_type;
res = device_register(&adap->dev); /*註冊*/
if (res)
goto out_list;
dev_dbg(&adap->dev, "adapter [%s] registered\n", adap->name);
#ifdef CONFIG_I2C_COMPAT
res = class_compat_create_link(i2c_adapter_compat_class, &adap->dev,
adap->dev.parent);
if (res)
dev_warn(&adap->dev,
"Failed to create compatibility class link\n");
#endif
/* 在這裏對已經添加好的I2C設備進行註冊 */
if (adap->nr < __i2c_first_dynamic_bus_num)
i2c_scan_static_board_info(adap);
/* Notify drivers */
mutex_lock(&core_lock);
bus_for_each_drv(&i2c_bus_type, NULL, adap, __process_new_adapter);
mutex_unlock(&core_lock);
return 0;
out_list:
mutex_lock(&core_lock);
idr_remove(&i2c_adapter_idr, adap->nr);
mutex_unlock(&core_lock);
return res;
}
static void i2c_scan_static_board_info(struct i2c_adapter *adapter)
{
struct i2c_devinfo *devinfo;
down_read(&__i2c_board_lock);
list_for_each_entry(devinfo, &__i2c_board_list, list) {
if (devinfo->busnum == adapter->nr
&& !i2c_new_device(adapter,
&devinfo->board_info))
dev_err(&adapter->dev,
"Can‘t create device at 0x%02x\n",
devinfo->board_info.addr);
}
up_read(&__i2c_board_lock);
}
3. I2C從設備的添加
int __init
i2c_register_board_info(int busnum,
struct i2c_board_info const *info, unsigned len)
{
int status;
down_write(&__i2c_board_lock);
/* */
if (busnum >= __i2c_first_dynamic_bus_num)
__i2c_first_dynamic_bus_num = busnum + 1;
for (status = 0; len; len--, info++) {
struct i2c_devinfo *devinfo;
devinfo = kzalloc(sizeof(*devinfo), GFP_KERNEL);
if (!devinfo) {
pr_debug("i2c-core: can‘t register boardinfo!\n");
status = -ENOMEM;
break;
}
/*放在哪個適配器上*/
devinfo->busnum = busnum;
devinfo->board_info = *info;
/*將所有的從設備都掛在一個鏈表中*/
list_add_tail(&devinfo->list, &__i2c_board_list);
}
up_write(&__i2c_board_lock);
return status;
}
4. AT24對於I2C的讀寫
只研究I2C，所以只是看下I2C在AT24C02中大概是如何使用，其他代碼都省略
static struct i2c_driver at24_driver = {
.driver = {
.name = "at24",
.owner = THIS_MODULE,
},
.probe = at24_probe,
.remove = __devexit_p(at24_remove),
.id_table = at24_ids, /*這是一個包含所有支持名字的列表，只要註冊的設備裏有其中一個名字匹配就匹配成功*/
};
static int __init at24_init(void)
{
。。。省略。。。
/*註冊從設備驅動*/
return i2c_add_driver(&at24_driver);
}
module_init(at24_init);
static inline int i2c_add_driver(struct i2c_driver *driver)
{
return i2c_register_driver(THIS_MODULE, driver);
}
從設備的註冊函數如下：
int i2c_register_driver(struct module *owner, struct i2c_driver *driver)
{
int res;
/* Can‘t register until after driver model init */
if (unlikely(WARN_ON(!i2c_bus_type.p)))
return -EAGAIN;
/* add the driver to the list of i2c drivers in the driver core */
driver->driver.owner = owner;
driver->driver.bus = &i2c_bus_type;
/*註冊設備*/
res = driver_register(&driver->driver);
if (res)
return res;
/* Drivers should switch to dev_pm_ops instead. */
if (driver->suspend)
pr_warn("i2c-core: driver [%s] using legacy suspend method\n",
driver->driver.name);
if (driver->resume)
pr_warn("i2c-core: driver [%s] using legacy resume method\n",
driver->driver.name);
pr_debug("i2c-core: driver [%s] registered\n", driver->driver.name);
INIT_LIST_HEAD(&driver->clients);
/* Walk the adapters that are already present */
i2c_for_each_dev(driver, __process_new_driver);
return 0;
}
static int at24_probe(struct i2c_client *client, const struct i2c_device_id *id)
{
if (client->dev.platform_data) {
chip = *(struct at24_platform_data *)client->dev.platform_data;
} else {
if (!id->driver_data) {
err = -ENODEV;
goto err_out;
}
/* Use I2C operations unless we‘re stuck with SMBus extensions. */
if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C)) {
if (chip.flags & AT24_FLAG_ADDR16) {
err = -EPFNOSUPPORT;
goto err_out;
}
/*查看支持的模式*/
if (i2c_check_functionality(client->adapter,
I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {
use_smbus = I2C_SMBUS_I2C_BLOCK_DATA;
} else if (i2c_check_functionality(client->adapter,
I2C_FUNC_SMBUS_READ_WORD_DATA)) {
use_smbus = I2C_SMBUS_WORD_DATA;
} else if (i2c_check_functionality(client->adapter,
I2C_FUNC_SMBUS_READ_BYTE_DATA)) {
use_smbus = I2C_SMBUS_BYTE_DATA;
} else {
err = -EPFNOSUPPORT;
goto err_out;
}
}
if (chip.flags & AT24_FLAG_TAKE8ADDR)
num_addresses = 8;
else
num_addresses = DIV_ROUND_UP(chip.byte_len,
(chip.flags & AT24_FLAG_ADDR16) ? 65536 : 256);
at24 = kzalloc(sizeof(struct at24_data) +
num_addresses * sizeof(struct i2c_client *), GFP_KERNEL);
if (!at24) {
err = -ENOMEM;
goto err_out;
} mutex_init(&at24->lock);
at24->use_smbus = use_smbus;
at24->chip = chip;
at24->num_addresses = num_addresses;
/*
* Export the EEPROM bytes through sysfs, since that‘s convenient.
* By default, only root should see the data (maybe passwords etc)
*/
sysfs_bin_attr_init(&at24->bin);
at24->bin.attr.name = "eeprom";
at24->bin.attr.mode = chip.flags & AT24_FLAG_IRUGO ? S_IRUGO : S_IRUSR;
at24->bin.read = at24_bin_read;
at24->bin.size = chip.byte_len;
at24->macc.read = at24_macc_read;
writable = !(chip.flags & AT24_FLAG_READONLY);
if (writable) {
if (!use_smbus || i2c_check_functionality(client->adapter,
I2C_FUNC_SMBUS_WRITE_I2C_BLOCK)) {
unsigned write_max = chip.page_size;
at24->macc.write = at24_macc_write;
at24->bin.write = at24_bin_write;
at24->bin.attr.mode |= S_IWUSR;
if (write_max > io_limit)
write_max = io_limit;
if (use_smbus && write_max > I2C_SMBUS_BLOCK_MAX)
write_max = I2C_SMBUS_BLOCK_MAX;
at24->write_max = write_max;
/* buffer (data + address at the beginning) */
at24->writebuf = kmalloc(write_max + 2, GFP_KERNEL);
if (!at24->writebuf) {
err = -ENOMEM;
goto err_struct;
}
} else {
dev_warn(&client->dev,
"cannot write due to controller restrictions.");
}
}
}
static ssize_t at24_bin_read(struct file *filp, struct kobject *kobj,
struct bin_attribute *attr,
char *buf, loff_t off, size_t count)
{
struct at24_data *at24;
at24 = dev_get_drvdata(container_of(kobj, struct device, kobj));
return at24_read(at24, buf, off, count);
}
然後一直往下追，在某部分功能會看到
static ssize_t at24_eeprom_read(struct at24_data *at24, char *buf,
unsigned offset, size_t count)
{
status = i2c_transfer(client->adapter, msg, 2);
}
drivers.c/i2c/i2c-core.c
int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
{
unsigned long orig_jiffies;
int ret, try;
if (adap->algo->master_xfer) {
if (in_atomic() || irqs_disabled()) {
ret = i2c_trylock_adapter(adap);
if (!ret)
/* I2C activity is ongoing. */
return -EAGAIN;
} else {
i2c_lock_adapter(adap);
}
/* Retry automatically on arbitration loss */
orig_jiffies = jiffies;
for (ret = 0, try = 0; try <= adap->retries; try++) {
ret = adap->algo->master_xfer(adap, msgs, num);
if (ret != -EAGAIN)
break;
if (time_after(jiffies, orig_jiffies + adap->timeout))
break;
}
i2c_unlock_adapter(adap);
return ret;
} else {
dev_dbg(&adap->dev, "I2C level transfers not supported\n");
return -EOPNOTSUPP;
}
}
在這裏，我們看到了adap->algo->master_xfer，也就是底層最終的傳輸函數。
Kernel的IIC驅動分析