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I2C

I2C基础知识：I2C总线占用两根信号线：SCL，SDAI2C由三部分组成：I2C core，I2C总线驱动，I2C设备驱动I2C体系结构：1> I2C核心：提供对总线驱动，设备驱动的注册，注销           探测设备，检测设备地址的上层代码2> I2C总线驱动：适配器的实现。包括适配器结构体i2c_adapter,i2c适配器对应的i2c_algorithm结构体，控制适配器产生通信信号。3> I2C设备驱动：对设备端的实现，包含i2c_driver和i2c_client。I2C设备的查看：tree /sys/bus/i2c/相关函数路径：kernel/msm-3.18/include/linux/i2c.h 结构体的声明kernel/msm-3.18/drivers/i2c :1. i2c-core.c 实现 核心功能和/proc/bus/i2c接口2. busses文件夹 I2C适配器控制器的驱动（platform_driver）3. algos 文件夹 适配器的通信方法i2c_algorithm提供了i2c_adapter所需要的通信函数来控制适配器产生特定的访问周期。i2c_driver与i2c_client的关系是一对多一个适配器可以连接多个I2C设备，故i2c_adapter和i2c_client的关系是一对多。有关：适配器驱动，适配器，I2C设备驱动，I2C设备，总线通信方法algorithm

数据结构之间的逻辑关系：

I2C适配器驱动的注册和注销（设备节点兼容性等）i2c总线控制器对应的platform_driver的probe()函数i2c-tegra.c描述的是platform的适配性代码：kernel/msm-3.18/drivers/i2c/busses/i2c-tegra.cTegra I2C 总线驱动#struct tegra_i2c_dev - per device i2c context设备的注册和注销：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);}兼容性数组：/* 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驱动初始化：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,    },};在与dts中描述的设备节点arch/arm/boot/dts/tegra20.dtsi做兼容性匹配compatible = "nvidia,tegra20-i2c"成功之后，会调用probe()函数进行回调。tegra_i2c_probe：初始化i2c所使用的硬件资源：（初始化适配器硬件，申请适配器要的内存base，时钟中断，最终注册适配器）base = devm_ioremap_resource(&pdev->dev, res);//内存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数据结构：i2c_set_adapdata(&i2c_dev->adapter, i2c_dev);//添加适配器            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通信结构体赋值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总线控制器对应的remove()函数会删除适配器等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总线的通信方法：static const struct i2c_algorithm tegra_i2c_algo = {     .master_xfer    = tegra_i2c_xfer,    .functionality  = tegra_i2c_func,};1.functionality 返回支持的通信协议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_xfertegra_i2c_xfer循环处理每条i2c-msg，确定end_type,调用tegra_i2c_xfer_msg根据消息的不同，实现开始位，数据的发送和接收，一个停止位。tegra_i2c_unmask_irq(i2c_dev, int_mask);//屏蔽中断ret = wait_for_completion_timeout(&i2c_dev->msg_complete, TEGRA_I2C_TIMEOUT);//睡眠，然后发送i2c-msgtegra_i2c_mask_irq(i2c_dev, int_mask);//解除中断信号的屏蔽

I2C设备驱动：1.初始化kernel/msm-3.18/drivers/i2c/i2c-core.cstatic 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.模块的加载和卸载static int __init i2c_init(void){...retval = i2c_add_driver(&dummy_driver);...}static void __exit i2c_exit(void){...i2c_del_driver(&dummy_driver);...}I2C驱动设备的数据传输是由I2C适配器所对应的algorithm来进行msg消息数组的处理的。(I2C适配器与algorithm兼属于I2C总线驱动模块)

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