I2C
I2C基础知识: I2C总线占用两根信号线:SCL,SDA I2C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.c Tegra 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_xfer tegra_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-msg tegra_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.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)