IMX6ULL 芯片的I2C_Adapter驱动分析

参考资料：

• Linux内核真正的I2C控制器驱动程序

  • IMX6ULL: Linux-4.9.88\drivers\i2c\busses\i2c-imx.c

I2C控制器内部结构

通用的简化结构

IMX6ULL的I2C控制器内部结构

I2C控制器操作方法

• 使能时钟、设置时钟

• 发送数据：

  • 把数据写入tx_register，等待中断发生

  • 中断发生后，判断状态：是否发生错误、是否得到回应信号(ACK)

  • 把下一个数据写入tx_register，等待中断：如此循环

• 接收数据：

  • 设置controller_register，进入接收模式，启动接收，等待中断发生

  • 中断发生后，判断状态，读取rx_register得到数据

  • 如此循环

分析代码

1. 设备树：IMX6ULL: arch/arm/boot/dts/imx6ull.dtsi

   i2c1: i2c@021a0000 {
   		#address-cells = <1>;
   		#size-cells = <0>;
   		compatible = "fsl,imx6ul-i2c", "fsl,imx21-i2c";
   		reg = <0x021a0000 0x4000>;
   		interrupts = <GIC_SPI 36 IRQ_TYPE_LEVEL_HIGH>;
   		clocks = <&clks IMX6UL_CLK_I2C1>;
   		status = "disabled";
   };
   

2. 入口函数：注册platform_driver，且确定了设备树匹配的of_device_id

   static struct platform_device_id imx_i2c_devtype[] = {
   	{
   		.name = "imx1-i2c",
   		.driver_data = (kernel_ulong_t)&imx1_i2c_hwdata,
   	}, {
   		.name = "imx21-i2c",
   		.driver_data = (kernel_ulong_t)&imx21_i2c_hwdata,
   	}, {
   		/* sentinel */
   	}
   };
   MODULE_DEVICE_TABLE(platform, imx_i2c_devtype);
   
   static const struct of_device_id i2c_imx_dt_ids[] = {
   	{ .compatible = "fsl,imx1-i2c", .data = &imx1_i2c_hwdata, },
   	{ .compatible = "fsl,imx21-i2c", .data = &imx21_i2c_hwdata, },
   	{ .compatible = "fsl,vf610-i2c", .data = &vf610_i2c_hwdata, },
   	{ /* sentinel */ }
   };
   MODULE_DEVICE_TABLE(of, i2c_imx_dt_ids);
   
   static struct platform_driver i2c_imx_driver = {
   	.probe = i2c_imx_probe,
   	.remove = i2c_imx_remove,
   	.driver	= {
   		.name = DRIVER_NAME,
   		.owner = THIS_MODULE,
   		.of_match_table = i2c_imx_dt_ids,
   		.pm = IMX_I2C_PM,
   	},
   	.id_table	= imx_i2c_devtype,
   };
   
   static int __init i2c_adap_imx_init(void)
   {
   	return platform_driver_register(&i2c_imx_driver);
   }
   

3. probe函数分析

   • 分配适配器

     

     注意：struct imx_i2c_struct里面已经有了适配器如下：

     

   • 设置适配器

     

   • 注册适配器

     

   当然在probe函数里面还有一些额外的操作，例如设置i2c控制器的时钟等如下：

   

4. 算法结构体分析

   

   如上图所示，具体的i2c读写数据就在i2c_imx_xfer里面。如下：

   static int i2c_imx_xfer(struct i2c_adapter *adapter,
   						struct i2c_msg *msgs, int num)
   {
   	unsigned int i, temp;
   	int result;
   	bool is_lastmsg = false;
   	struct imx_i2c_struct *i2c_imx = i2c_get_adapdata(adapter);
   
   	dev_dbg(&i2c_imx->adapter.dev, "<%s>\n", __func__);
   
   	/* Start I2C transfer */
   	result = i2c_imx_start(i2c_imx); 
   	if (result)
   		goto fail0;
   
   	/* read/write data */
   	for (i = 0; i < num; i++) {
   		if (i == num - 1)
   			is_lastmsg = true;
   
   		if (i) {
   			temp = imx_i2c_read_reg(i2c_imx, IMX_I2C_I2CR);// 1.发起开始信号
   			temp |= I2CR_RSTA;
   			imx_i2c_write_reg(temp, i2c_imx, IMX_I2C_I2CR);
   			result =  i2c_imx_bus_busy(i2c_imx, 1);
   			if (result)
   				goto fail0;
   		}
   
   		/* write/read data */
   		if (msgs[i].flags & I2C_M_RD)
   			result = i2c_imx_read(i2c_imx, &msgs[i], is_lastmsg);
   		else {
   			if (i2c_imx->dma && msgs[i].len >= DMA_THRESHOLD)
   				result = i2c_imx_dma_write(i2c_imx, &msgs[i]);
   			else
   				result = i2c_imx_write(i2c_imx, &msgs[i]);
   		}
   		if (result)
   			goto fail0;
   	}
   
   fail0:
   	/* Stop I2C transfer */
   	i2c_imx_stop(i2c_imx); 
   
   	return (result < 0) ? result : num;
   }
   

   函数i2c_imx_xfer读操作i2c_imx_read分析：