I2C

I2C

I2C基礎知識：
I2C總線佔用兩根信號線：SCL，SDA
I2C由三部分組成：I2C core，I2C總線驅動，I2C設備驅動
I2C體系結構：
1> I2C核心：提供對總線驅動，設備驅動的註冊，註銷
           探測設備，檢測設備地址的上層代碼
2> I2C總線驅動：適配器的實現。包括適配器結構體i2c_adapter,i2c適配器對應的i2c_algorithm結構體，控制適配器產生通信信號。
3> I2C設備驅動：對設備端的實現，包含i2c_driver和i2c_client。
I2C設備的查看：
tree /sys/bus/i2c/
相關函數路徑：kernel/msm-3.18/include/linux/i2c.h 結構體的聲明
kernel/msm-3.18/drivers/i2c :
1. i2c-core.c 實現 核心功能和/proc/bus/i2c接口
2. busses文件夾 I2C適配器控制器的驅動（platform_driver）
3. algos 文件夾 適配器的通信方法
i2c_algorithm提供了i2c_adapter所需要的通信函數來控制適配器產生特定的訪問週期。

i2c_driver與i2c_client的關係是一對多
一個適配器可以連接多個I2C設備，故i2c_adapter和i2c_client的關係是一對多。

有關：適配器驅動，適配器，I2C設備驅動，I2C設備，總線通信方法algorithm

數據結構之間的邏輯關係：

I2C適配器驅動的註冊和註銷（設備節點兼容性等）
i2c總線控制器對應的platform_driver的probe()函數
i2c-tegra.c描述的是platform的適配性
代碼：kernel/msm-3.18/drivers/i2c/busses/i2c-tegra.c
Tegra I2C 總線驅動
#struct tegra_i2c_dev - per device i2c context
設備的註冊和註銷：
static int __init tegra_i2c_init_driver(void)
{
    return platform_driver_register(&tegra_i2c_driver);
}

static void __exit tegra_i2c_exit_driver(void)
{
    platform_driver_unregister(&tegra_i2c_driver);
}

兼容性數組：
/* Match table for of_platform binding */
static const struct of_device_id tegra_i2c_of_match[] = { 
    { .compatible = "nvidia,tegra114-i2c", .data = &tegra114_i2c_hw, },
    { .compatible = "nvidia,tegra30-i2c", .data = &tegra30_i2c_hw, },
    { .compatible = "nvidia,tegra20-i2c", .data = &tegra20_i2c_hw, },
    { .compatible = "nvidia,tegra20-i2c-dvc", .data = &tegra20_i2c_hw, },
    {}, 
};
MODULE_DEVICE_TABLE(of, tegra_i2c_of_match);

platform驅動初始化：
static struct platform_driver tegra_i2c_driver = { 
    .probe   = tegra_i2c_probe,
    .remove  = tegra_i2c_remove,
    .driver  = {
        .name  = "tegra-i2c",
        .owner = THIS_MODULE,
        .of_match_table = tegra_i2c_of_match,
        .pm    = TEGRA_I2C_PM,
    },
};
在與dts中描述的設備節點arch/arm/boot/dts/tegra20.dtsi做兼容性匹配compatible = "nvidia,tegra20-i2c"成功之後，會調用probe()函數進行回調。
tegra_i2c_probe：
初始化i2c所使用的硬件資源：（初始化適配器硬件，申請適配器要的內存base，時鐘中斷，最終註冊適配器）
base = devm_ioremap_resource(&pdev->dev, res);//內存
i2c_dev->base = base; 
i2c_dev->div_clk = div_clk;
i2c_dev->irq = irq;
i2c_dev->cont_id = pdev->id;
i2c_dev->dev = &pdev->dev;
i2c_dev->rst = devm_reset_control_get(&pdev->dev, "i2c");
i2c_dev->hw = &tegra20_i2c_hw;
platform_set_drvdata(pdev, i2c_dev);//
fast_clk = devm_clk_get(&pdev->dev, "fast-clk");
i2c_dev->fast_clk = fast_clk;
of_property_read_u32(i2c_dev->dev->of_node, "clock-frequency",&i2c_dev->bus_clk_rate);
添加i2c_adapter數據結構：
i2c_set_adapdata(&i2c_dev->adapter, i2c_dev);//添加適配器            
i2c_dev->adapter.owner = THIS_MODULE;
i2c_dev->adapter.class = I2C_CLASS_DEPRECATED;
strlcpy(i2c_dev->adapter.name, "Tegra I2C adapter",
        sizeof(i2c_dev->adapter.name));
i2c_dev->adapter.algo = &tegra_i2c_algo;//algo通信結構體賦值
i2c_dev->adapter.dev.parent = &pdev->dev;
i2c_dev->adapter.nr = pdev->id;
i2c_dev->adapter.dev.of_node = pdev->dev.of_node;
i2c_add_numbered_adapter(&i2c_dev->adapter);
i2c總線控制器對應的remove()函數會刪除適配器等
static int tegra_i2c_remove(struct platform_device *pdev)
{
    struct tegra_i2c_dev *i2c_dev = platform_get_drvdata(pdev);
    i2c_del_adapter(&i2c_dev->adapter);

    clk_unprepare(i2c_dev->div_clk);                                                                                                                           
    if (!i2c_dev->hw->has_single_clk_source)
        clk_unprepare(i2c_dev->fast_clk);

    return 0;
}

---

I2C總線的通信方法：
static const struct i2c_algorithm tegra_i2c_algo = { 
    .master_xfer    = tegra_i2c_xfer,
    .functionality  = tegra_i2c_func,
};
1.functionality 返回支持的通信協議
static u32 tegra_i2c_func(struct i2c_adapter *adap) 
{
   struct tegra_i2c_dev *i2c_dev = i2c_get_adapdata(adap);
    u32 ret = I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL | I2C_FUNC_10BIT_ADDR | I2C_FUNC_PROTOCOL_MANGLING;
    if (i2c_dev->hw->has_continue_xfer_support)
        ret |= I2C_FUNC_NOSTART;
    return ret;
}
2.tegra_i2c_xfer
tegra_i2c_xfer循環處理每條i2c-msg，確定end_type,調用tegra_i2c_xfer_msg根據消息的不同，實現開始位，數據的發送和接收，一個停止位。tegra_i2c_unmask_irq(i2c_dev, int_mask);//屏蔽中斷
ret = wait_for_completion_timeout(&i2c_dev->msg_complete, TEGRA_I2C_TIMEOUT);//睡眠，然後發送i2c-msg
tegra_i2c_mask_irq(i2c_dev, int_mask);//解除中斷信號的屏蔽

---

I2C設備驅動：
1.初始化
kernel/msm-3.18/drivers/i2c/i2c-core.c
static struct i2c_driver dummy_driver = {         
    .driver.name    = "dummy",  //名字一致也可以兼容 
    .probe      = dummy_probe,                    
    .remove     = dummy_remove, 
    .id_table   = dummy_id,                       
};
2.模塊的加載和卸載
static int __init i2c_init(void)
{
...
retval = i2c_add_driver(&dummy_driver);
...
}

static void __exit i2c_exit(void)
{
...
i2c_del_driver(&dummy_driver);
...
}
I2C驅動設備的數據傳輸是由I2C適配器所對應的algorithm來進行msg消息數組的處理的。(I2C適配器與algorithm兼屬於I2C總線驅動模塊)