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MTK Aandroid 底层驱动-----I2C读写函数分析

2016-9-19 23:49:58 8232

0 本帖最后由 ycd37850105 于 2016-9-19 23:51 编辑使用camera imgsensor部分的i2c读写程序进行分析。先亮剑（代码）代码目录：mediatek/custom/common/kernel/imgsensor/src/kd_sensorlist.c /************************************************************************** 功能：读取从机数据 iReadRegI2C函数调用i2c_master_send函数来发送从机寄存器地址，接着调用i2c_master_recv函数来发送读地址并读取寄存器中的值。参数： a_pSendData：寄存器的地址 a_sizeSendData：寄存器地址的字节数 a_pRecvData：读取数据存放区 a_sizeRecvData：读取数据字节数 i2cId：读地址 ************************************************************************/ int iReadRegI2C(u8 a_pSendData , u16 a_sizeSendData, u8 * a_pRecvData, u16 a_sizeRecvData, u16 i2cId) { int i4RetValue = 0; spin_lock(&kdsensor_drv_lock); g_psti2Cclient->addr = (i2cId >> 1); spin_unlock(&kdsensor_drv_lock); i4RetValue = i2c_master_send(g_pstI2Cclient, (char )a_pSendData, a_sizeSendData); if (i4RetValue != a_sizeSendData) { PK_DBG("[CAMERA SENSOR] I2C send failed!!, Addr = 0x%xn", a_pSendData[0]); return -1; } i4RetValue = i2c_master_recv(g_pstI2Cclient, (char )a_pRecvData, a_sizeRecvData); if (i4RetValue != a_sizeRecvData) { PK_DBG("[CAMERA SENSOR] I2C read failed!! n"); return -1; } return 0; } /************************************************************************** 功能：向从机写入数据 iWriteRegI2C函数调用i2c_master_send函数来发送从机寄存器地址和要写入该寄存器的数据。参数： a_pSendData：要写入的数据（包括寄存器地址和写入寄存器的数据） a_sizeSendData：发送数据字节数 i2cId：写地址 ************************************************************************/ int iWriteRegI2C(u8 a_pSendData , u16 a_sizeSendData, u16 i2cId) { int i4RetValue = 0; int retry = 3; spin_lock(&kdsensor_drv_lock); g_pstI2Cclient->addr = (i2cId >> 1); spin_unlock(&kdsensor_drv_lock); do { i4RetValue = i2c_master_send(g_pstI2Cclient, a_pSendData, a_sizeSendData); if (i4RetValue != a_sizeSendData) { PK_DBG("[CAMERA SENSOR] I2C send failed!!, Addr = 0x%x, Data = 0x%x n", a_pSendData[0], a_pSendData[1] ); } else { break; } uDELAY(50); } while ((retry--) > 0); return 0; } 我们追溯i2c_master_send和i2c_master_recv函数。代码目录：kernel/drivers/i2c/i2c-core.c /** * i2c_master_send - issue a single I2C message in master transmit mode * @client: Handle to slave device * @buf: Data that will be written to the slave * @count: How many bytes to write, must be less than 64k since msg.len is u16 * * Returns negative errno, or else the number of bytes written. / int i2c_master_send(const struct i2c_client client, const char buf, int count) { int ret; struct i2c_adapter adap = client->adapter; struct i2c_msg msg; msg.addr = client->addr; msg.flags = client->flags & I2C_M_TEN; msg.timing = client->timing; msg.len = count; msg.buf = (char )buf; msg.ext_flag = client->ext_flag; ret = i2c_transfer(adap, &msg, 1); / * If everything went ok (i.e. 1 msg transmitted), return #bytes * transmitted, else error code. / return (ret == 1) ? count : ret; } /* * i2c_master_recv - issue a single I2C message in master receive mode * @client: Handle to slave device * @buf: Where to store data read from slave * @count: How many bytes to read, must be less than 64k since msg.len is u16 * * Returns negative errno, or else the number of bytes read. / int i2c_master_recv(const struct i2c_client client, char buf, int count) { struct i2c_adapter adap = client->adapter; struct i2c_msg msg; int ret; msg.addr = client->addr; msg.flags = client->flags & I2C_M_TEN; msg.flags \|= I2C_M_RD; msg.timing = client->timing; msg.len = count; msg.buf = buf; msg.ext_flag = client->ext_flag; ret = i2c_transfer(adap, &msg, 1); /* * If everything went ok (i.e. 1 msg received), return #bytes received, * else error code. / return (ret == 1) ? count : ret; } 从源代码中我们可以看出i2c_master_recv和i2c_master_send函数都是对single I2C message 进行处理的，即msg结构体中只有一个消息要处理。对于前面的iReadRegI2C函数，它读取数据需要处理两个消息（一条写消息，一条读消息），因此iReadRegI2C函数可以用下面所示方法实现： int iReadRegI2C(u8 a_pSendData , u16 a_sizeSendData, u8 * a_pRecvData, u16 a_sizeRecvData, u16 i2cId) { int i4RetValue = 0; spin_lock(&kdsensor_drv_lock); g_pstI2Cclient->addr = (i2cId >> 1) spin_unlock(&kdsensor_drv_lock); struct i2c_msg msgs[] = { { .addr = g_pstI2Cclient->addr, .flags = 0, .timing= g_pstI2Cclient->timing, .len = a_sizeSendData, .buf = a_pSendData, .ext_flag = g_pstI2Cclient->ext_flag, }, { .addr = g_pstI2Cclient->addr, .flags = I2C_M_RD, .len = a_sizeRecvData, .timing= g_pstI2Cclient->timing, .buf = a_pRecvData, .ext_flag = g_pstI2Cclient->ext_flag, }, }; i4RetValue = i2c_transfer(g_pstI2Cclient->adapter, msgs, 2); if(i4RetValue < 0) { PK_DBG("[CAMERA SENSOR] I2C send failed!!, Addr = 0x%xn", a_pSendData[0]); return -1; } } 不管iReadRegI2C函数用哪种方式实现，它最终都会调用到i2c_transfer函数，因为所有读写消息都会传递给i2c_transfer处理。i2c_transfer函数本身不具备驱动适配器物理硬件完成消息交互的能力，它只是寻找到i2c_adapter对应的i2c_algorithm，并使用i2c_algorithm的master_xfer()函数真正驱动硬件流程。 i2c_transfer处理消息机制：非restart模式下，i2c_transfer函数所引发的对数据读写时序如图1所示，它对每一条消息的处理都会引发开始和停止信号，有多少条消息就会出现多少个开始和停止信号。图 1 非restart模式下对应时序 restart模式下的时序如图2所示，我们发现整个消息处理过程就只产生一个开始信号和一个停止信号，而时序中会出现restart信号，它仅仅使用一个消息处理。图 2 restart模式下对应时序前面所讲的camera imagesensor中的i2c读写函数都是工作在非restart模式下的，而很多稍微复杂一些的i2c设备并不遵循这一读写流程，前段时间在Android平台下调试视频解码芯片ADV7280的i2c通信时就出现了只能写入不能读出的问题，后来仔细查看ADV7280的i2c读写流程时发现，它读数据是在restart模式下，而测试代码是引用了camera imagesensor中的i2c读写函数，因而没有restart信号，读不出数据也是必然了。ADV7280的读写流程如图3所示。图 3 ADV7280读数据流程最后经过调整引入restart模式，i2c读OK！调整后的iReadRegI2C函数： /************************************************************************* 功能：restart模式下读取从机数据，调用i2c_master_send完成写寄存器地址和读寄存器内容的过程（不需要调用i2c_master_recv读取）。参数： a_pData：先传入寄存器地址，最后作为读取数据的缓冲区 a_sizeData：高八位为寄存器地址字节数，低八位为接收数据字节数 I2cId：读地址 ************************************************************************/ int iReadRegI2C(u8 a_pData , u16 a_sizeData , u16 i2cId) { int i4RetValue = 0; spin_lock(&kdsensor_drv_lock); g_pstI2Cclient->addr = (i2cId >> 1) & I2C_MASK_FLAG \| I2C_WR_FLAG \| I2C_RS_FLAG;//加入I2C_RS_FLAG，实现restart模式 spin_unlock(&kdsensor_drv_lock); i4RetValue = i2c_master_send(g_pstI2Cclient, a_pData, a_sizeData); if (i4RetValue != a_sizeData) { PK_DBG("[CAMERA SENSOR] I2C send failed!!, Addr = 0x%xn", a_pData[0]); return -1; } g_pstI2Cclient->addr &= I2C_MASK_FLAG; return 0; } 0
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