六:其它的扩展分析完adapter和i2c driver的注册之后,好像整个架构也差不多了,其它,扩展的东西还有很多.我们举一个legacy形式的例子,这个例子是在kernel中随便搜索出来的:在linux-2.6.26.3/drivers/hwmon/ad7418.c中,初始化函数为:static int __init ad7418_init(void){ return i2c_add_driver(&ad7418_driver);}i2c_driver ad7418_driver结构如下:static struct i2c_driver ad7418_driver = { .driver = { .name = “ad7418”, }, .attach_adapter = ad7418_attach_adapter, .detach_client = ad7418_detach_client,};该结构中没有probe()函数,可以断定是一个legacy形式的驱动.这类驱动注册的时候,会调用driver的attach_adapter函数.在这里也就是ad7418_attach_adapter.这个函数代码如下:static int ad7418_attach_adapter(struct i2c_adapter *adapter){ if (!(adapter->class & I2C_CLASS_HWMON)) return 0; return i2c_probe(adapter, &addr_data, ad7418_detect);}在这里我们又遇到了一个i2c-core中的函数,i2c_probe().在分析这个函数之前,先来看下addr_data是什么?#define I2C_CLIENT_MODULE_PARM(var,desc) / static unsigned short var[I2C_CLIENT_MAX_OPTS] = I2C_CLIENT_DEFAULTS; / static unsigned int var##_num; / module_param_array(var, short, &var##_num, 0); / MODULE_PARM_DESC(var,desc)#define I2C_CLIENT_MODULE_PARM_FORCE(name) /I2C_CLIENT_MODULE_PARM(force_##name, / “List of adapter,address pairs which are ” / “unquestionably assumed to contain a `” / # name “‘ chip”)#define I2C_CLIENT_INSMOD_COMMON /I2C_CLIENT_MODULE_PARM(probe, “List of adapter,address pairs to scan ” / “additionally”); /I2C_CLIENT_MODULE_PARM(ignore, “List of adapter,address pairs not to ” / “scan”); /static const struct i2c_client_address_data addr_data = { / .normal_i2c = normal_i2c, / .probe = probe, / .ignore = ignore, / .forces = forces, /}#define I2C_CLIENT_FORCE_TEXT / “List of adapter,address pairs to boldly assume to be present”由此可知道,addr_data中的三个成员都是模块参数.在加载模块的时候可以用参数的方式对其赋值.三个模块参数为别为probe,ignore,force.另外需要指出的是normal_i2c不能以模块参数的方式对其赋值,只能在驱动内部静态指定.从模块参数的模述看来, probe是指”List of adapter,address pairs to scan additionally”Ignore是指”List of adapter,address pairs not to scan “Force是指”List of adapter,address pairs to boldly assume to be present” 事实上,它们里面的数据都是成对出现的.前面一部份表示所在的总线号,ANY_I2C_BUS表示任一总线.后一部份表示设备的地址.现在可以来跟踪i2c_probe()的代码了.如下:int i2c_probe(struct i2c_adapter *adapter, const struct i2c_client_address_data *address_data, int (*found_proc) (struct i2c_adapter *, int, int)){ int i, err; int adap_id = i2c_adapter_id(adapter); /* Force entries are done first, and are not affected by ignore entries */ //先扫描force里面的信息,注意它是一个二级指针.ignore里的信息对它是无效的 if (address_data->forces) { const unsigned short * const *forces = address_data->forces; int kind; for (kind = 0; forces[kind]; kind++) { for (i = 0; forces[kind][i] != I2C_CLIENT_END; i += 2) { if (forces[kind][i] == adap_id || forces[kind][i] == ANY_I2C_BUS) { dev_dbg(&adapter->dev, “found force ” “parameter for adapter %d, ” “addr 0x%02x, kind %d/n”, adap_id, forces[kind][i + 1], kind); err = i2c_probe_address(adapter, forces[kind][i + 1], kind, found_proc); if (err) return err; } } } } /* Stop here if we can’t use SMBUS_QUICK *///如果adapter不支持quick.不能够遍历这个adapter上面的设备 if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_QUICK)) { if (address_data->probe[0] == I2C_CLIENT_END && address_data->normal_i2c[0] == I2C_CLIENT_END) return 0; dev_warn(&adapter->dev, “SMBus Quick command not supported, ” “can’t probe for chips/n”); return -1; } /* Probe entries are done second, and are not affected by ignore entries either */ //遍历probe上面的信息.ignore上的信息也对它是没有影响的 for (i = 0; address_data->probe[i] != I2C_CLIENT_END; i += 2) { if (address_data->probe[i] == adap_id || address_data->probe[i] == ANY_I2C_BUS) { dev_dbg(&adapter->dev, “found probe parameter for ” “adapter %d, addr 0x%02x/n”, adap_id, address_data->probe[i + 1]); err = i2c_probe_address(adapter, address_data->probe[i + 1], -1, found_proc); if (err) return err; } } /* Normal entries are done last, unless shadowed by an ignore entry */ //最后遍历normal_i2c上面的信息.它上面的信息不能在ignore中. for (i = 0; address_data->normal_i2c[i] != I2C_CLIENT_END; i += 1) { int j, ignore; ignore = 0; for (j = 0; address_data->ignore[j] != I2C_CLIENT_END; j += 2) { if ((address_data->ignore[j] == adap_id || address_data->ignore[j] == ANY_I2C_BUS) && address_data->ignore[j + 1] == address_data->normal_i2c[i]) { dev_dbg(&adapter->dev, “found ignore ” “parameter for adapter %d, ” “addr 0x%02x/n”, adap_id, address_data->ignore[j + 1]); ignore = 1; break; } } if (ignore) continue; dev_dbg(&adapter->dev, “found normal entry for adapter %d, ” “addr 0x%02x/n”, adap_id, address_data->normal_i2c[i]); err = i2c_probe_address(adapter, address_data->normal_i2c[i], -1, found_proc); if (err) return err; } return 0;} 这段代码很简单,结合代码上面添加的注释应该很好理解.如果匹配成功,则会调用i2c_probe_address ().这个函数代码如下:static int i2c_probe_address(struct i2c_adapter *adapter, int addr, int kind, int (*found_proc) (struct i2c_adapter *, int, int)){ int err; /* Make sure the address is valid */ //地址小于0x03或者大于0x77都是不合法的 if (addr < 0x03 || addr > 0x77) { dev_warn(&adapter->dev, “Invalid probe address 0x%02x/n”, addr); return -EINVAL; } /* Skip if already in use */ //adapter上已经有这个设备了 if (i2c_check_addr(adapter, addr)) return 0; /* Make sure there is something at this address, unless forced */ //如果kind小于0.检查adapter上是否有这个设备 if (kind < 0) { if (i2c_smbus_xfer(adapter, addr, 0, 0, 0, I2C_SMBUS_QUICK, NULL) < 0) return 0; /* prevent 24RF08 corruption */ if ((addr & ~0x0f) == 0x50) i2c_smbus_xfer(adapter, addr, 0, 0, 0, I2C_SMBUS_QUICK, NULL); } /* Finally call the custom detection function */ //调用回调函数 err = found_proc(adapter, addr, kind); /* -ENODEV can be returned if there is a chip at the given address but it isn’t supported by this chip driver. We catch it here as this isn’t an error. */ if (err == -ENODEV) err = 0; if (err) dev_warn(&adapter->dev, “Client creation failed at 0x%x (%d)/n”, addr, err); return err;}首先,对传入的参数进行一系列的合法性检查.另外,如果该adapter上已经有了这个地址的设备了.也会返回失败.所有adapter下面的设备都是以adapter->dev为父结点的.因此只需要遍历adapter->dev下面的子设备就可以得到当前地址是不是被占用了.如果kind < 0.还得要adapter检查该总线是否有这个地址的设备.方法是向这个地址发送一个Read的Quick请求.如果该地址有应答,则说明这个地址上有这个设备.另外还有一种情况是在24RF08设备的特例.如果adapter上确实有这个设备,就会调用驱动调用时的回调函数.在上面涉及到了IIC的传输方式,有疑问的可以参考intel ICH5手册的有关smbus部份.跟踪i2c_smbus_xfer().代码如下:s32 i2c_smbus_xfer(struct i2c_adapter * adapter, u16 addr, unsigned short flags, char read_write, u8 command, int size, union i2c_smbus_data * data){ s32 res; flags &= I2C_M_TEN | I2C_CLIENT_PEC; if (adapter->algo->smbus_xfer) { mutex_lock(&adapter->bus_lock); res = adapter->algo->smbus_xfer(adapter,addr,flags,read_write, command,size,data); mutex_unlock(&adapter->bus_lock); } else res = i2c_smbus_xfer_emulated(adapter,addr,flags,read_write, command,size,data); return res;}如果adapter有smbus_xfer()函数,则直接调用它发送,否则,也就是在adapter不支持smbus协议的情况下,调用i2c_smbus_xfer_emulated()继续处理.跟进i2c_smbus_xfer_emulated().代码如下:static s32 i2c_smbus_xfer_emulated(struct i2c_adapter * adapter, u16 addr, unsigned short flags, char read_write, u8 command, int size, union i2c_smbus_data * data){ /* So we need to generate a series of msgs. In the case of writing, we need to use only one message; when reading, we need two. We initialize most things with sane defaults, to keep the code below somewhat simpler. */ //写操作只会进行一次交互,而读操作,有时会有两次操作. //因为有时候读操作要先写command,再从总线上读数据 //在这里为了代码的简洁.使用了两个缓存区,将两种情况统一起来. unsigned char msgbuf0[I2C_SMBUS_BLOCK_MAX+3]; unsigned char msgbuf1[I2C_SMBUS_BLOCK_MAX+2]; //一般来说,读操作要交互两次.例外的情况我们在下面会接着分析 int num = read_write == I2C_SMBUS_READ?2:1; //与设备交互的数据,一般在msg[0]存放写入设备的信息,在msb[1]里存放接收到的 //信息.不过也有例外的 //msg[2]的初始化,默认发送缓存区占一个字节,无接收缓存 struct i2c_msg msg[2] = { { addr, flags, 1, msgbuf0 }, { addr, flags | I2C_M_RD, 0, msgbuf1 } }; int i; u8 partial_pec = 0; //将要发送的信息copy到发送缓存区的第一字节 msgbuf0[0] = command; switch(size) { //quick类型的,其它并不传输有效数据,只是将地址写到总线上,等待应答即可 //所以将发送缓存区长度置为0 .再根据读/写操作,调整msg[0]的标志位 //这类传输只需要一次总线交互 case I2C_SMBUS_QUICK: msg[0].len = 0; /* Special case: The read/write field is used as data */ msg[0].flags = flags | (read_write==I2C_SMBUS_READ)?I2C_M_RD:0; num = 1; break; case I2C_SMBUS_BYTE: //BYTE类型指一次写和读只有一个字节.这种情况下,读和写都只会交互一次 //这种类型的读有例外,它读取出来的数据不是放在msg[1]中的,而是存放在msg[0] if (read_write == I2C_SMBUS_READ) { /* Special case: only a read! */ msg[0].flags = I2C_M_RD | flags; num = 1; } break; case I2C_SMBUS_BYTE_DATA: //Byte_Data是指命令+数据的传输形式.在这种情况下,写只需要一次交互,读却要两次 //第一次将command写到总线上,第二次要转换方向.要将设备地址和read标志写入总线. //应回答之后再进行read操作 //写操作占两字节,分别是command+data.读操作的有效数据只有一个字节 //交互次数用初始化值就可以了 if (read_write == I2C_SMBUS_READ) msg[1].len = 1; else { msg[0].len = 2; msgbuf0[1] = data->byte; } break; case I2C_SMBUS_WORD_DATA: //Word_Data是指命令+双字节的形式.这种情况跟Byte_Data的情况类似 //两者相比只是交互的数据大小不同 if (read_write == I2C_SMBUS_READ) msg[1].len = 2; else { msg[0].len=3; msgbuf0[1] = data->word & 0xff; msgbuf0[2] = data->word >> 8; } break; case I2C_SMBUS_PROC_CALL: //Proc_Call的方式与write 的Word_Data相似,只不过写完Word_Data之后,要等待它的应答 //应该它需要交互两次,一次写一次读 num = 2; /* Special case */ read_write = I2C_SMBUS_READ; msg[0].len = 3; msg[1].len = 2; msgbuf0[1] = data->word & 0xff; msgbuf0[2] = data->word >> 8; break; case I2C_SMBUS_BLOCK_DATA: //Block_Data:指command+N段数据的情况. //如果是读操作,它首先要写command到总线,然后再读N段数据.要写的command已经 //放在msg[0]了.现在只需要将msg[1]的标志置I2C_M_RECV_LEN位,msg[1]有效长度为1字节.因为 //adapter驱动会处理好的.现在现在还不知道要传多少段数据. //对于写的情况:msg[1]照例不需要.将要写的数据全部都放到msb[0]中.相应的也要更新 //msg[0]中的缓存区长度 if (read_write == I2C_SMBUS_READ) { msg[1].flags |= I2C_M_RECV_LEN; msg[1].len = 1; /* block length will be added by the underlying bus driver */ } else { //data->block[0]表示后面有多少段数据.总长度要加2是因为command+count+N段数据 msg[0].len = data->block[0] + 2; if (msg[0].len > I2C_SMBUS_BLOCK_MAX + 2) { dev_err(&adapter->dev, “smbus_access called with ” “invalid block write size (%d)/n”, data->block[0]); return -1; } for (i = 1; i < msg[0].len; i++) msgbuf0[i] = data->block[i-1]; } break; case I2C_SMBUS_BLOCK_PROC_CALL: //Proc_Call:表示写完Block_Data之后,要等它的应答消息它和Block_Data相比,只是多了一部份应答而已 num = 2; /* Another special case */ read_write = I2C_SMBUS_READ; if (data->block[0] > I2C_SMBUS_BLOCK_MAX) { dev_err(&adapter->dev, “%s called with invalid ” “block proc call size (%d)/n”, __func__, data->block[0]); return -1; } msg[0].len = data->block[0] + 2; for (i = 1; i < msg[0].len; i++) msgbuf0[i] = data->block[i-1]; msg[1].flags |= I2C_M_RECV_LEN; msg[1].len = 1; /* block length will be added by the underlying bus driver */ break; case I2C_SMBUS_I2C_BLOCK_DATA: //I2c Block_Data与Block_Data相似,只不过read的时候,数据长度是预先定义好了的.另外 //与Block_Data相比,中间不需要传输Count字段.(Count表示数据段数目) if (read_write == I2C_SMBUS_READ) { msg[1].len = data->block[0]; } else { msg[0].len = data->block[0] + 1; if (msg[0].len > I2C_SMBUS_BLOCK_MAX + 1) { dev_err(&adapter->dev, “i2c_smbus_xfer_emulated called with ” “invalid block write size (%d)/n”, data->block[0]); return -1; } for (i = 1; i <= data->block[0]; i++) msgbuf0[i] = data->block[i]; } break; default: dev_err(&adapter->dev, “smbus_access called with invalid size (%d)/n”, size); return -1; }//如果启用了PEC.Quick和I2c Block_Data是不支持PEC的 i = ((flags & I2C_CLIENT_PEC) && size != I2C_SMBUS_QUICK && size != I2C_SMBUS_I2C_BLOCK_DATA); if (i) { /* Compute PEC if first message is a write */ //如果第一个操作是写操作 if (!(msg[0].flags & I2C_M_RD)) { //如果只是写操作 if (num == 1) /* Write only */ //如果只有写操作,写缓存区要扩充一个字节,用来存放计算出来的PEC i2c_smbus_add_pec(&msg[0]); else /* Write followed by read */ //如果后面还有读操作,先计算前面写部份的PEC(注意这种情况下不需要 //扩充写缓存区,因为不需要发送PEC.只会接收到PEC) partial_pec = i2c_smbus_msg_pec(0, &msg[0]); } /* Ask for PEC if last message is a read */ //如果最后一次是读消息.还要接收到来自slave的PEC.所以接收缓存区要扩充一个字节 if (msg[num-1].flags & I2C_M_RD) msg[num-1].len++; } if (i2c_transfer(adapter, msg, num) < 0) return -1; /* Check PEC if last message is a read */ //操作完了之后,如果最后一个操作是PEC的读操作.检验后面的PEC是否正确 if (i && (msg[num-1].flags & I2C_M_RD)) { if (i2c_smbus_check_pec(partial_pec, &msg[num-1]) < 0) return -1; } //操作完了,现在可以将数据放到data部份返回了. if (read_write == I2C_SMBUS_READ) switch(size) { case I2C_SMBUS_BYTE: data->byte = msgbuf0[0]; break; case I2C_SMBUS_BYTE_DATA: data->byte = msgbuf1[0]; break; case I2C_SMBUS_WORD_DATA: case I2C_SMBUS_PROC_CALL: data->word = msgbuf1[0] | (msgbuf1[1] << 8); break; case I2C_SMBUS_I2C_BLOCK_DATA: for (i = 0; i < data->block[0]; i++) data->block[i+1] = msgbuf1[i]; break; case I2C_SMBUS_BLOCK_DATA: case I2C_SMBUS_BLOCK_PROC_CALL: for (i = 0; i < msgbuf1[0] + 1; i++) data->block[i] = msgbuf1[i]; break; } return 0;}在这个函数添上了很详细的注释,配和intel的datasheet,应该很容易看懂.在上面的交互过程中,调用了子函数i2c_transfer().它的代码如下所示:int i2c_transfer(struct i2c_adapter * adap, struct i2c_msg *msgs, int num){ int ret; if (adap->algo->master_xfer) {#ifdef DEBUG for (ret = 0; ret < num; ret++) { dev_dbg(&adap->dev, “master_xfer[%d] %c, addr=0x%02x, ” “len=%d%s/n”, ret, (msgs[ret].flags & I2C_M_RD) ? ‘R’ : ‘W’, msgs[ret].addr, msgs[ret].len, (msgs[ret].flags & I2C_M_RECV_LEN) ? “+” : “”); }#endif if (in_atomic() || irqs_disabled()) { ret = mutex_trylock(&adap->bus_lock); if (!ret) /* I2C activity is ongoing. */ return -EAGAIN; } else { mutex_lock_nested(&adap->bus_lock, adap->level); } ret = adap->algo->master_xfer(adap,msgs,num); mutex_unlock(&adap->bus_lock); return ret; } else { dev_dbg(&adap->dev, “I2C level transfers not supported/n”); return -ENOSYS; }}因为在这里的同步用的是mutex.首先判断判断是否充许睡眠,如果不允许,尝试获锁.如果获锁失败,则返回,这样的操作是避免进入睡眠,我们在后面也可以看到,实际的传输工作交给了adap->algo->master_xfer()完成.在这里,我们终于把i2c_probe_address()的执行分析完了,经过这个分析,我们也知道了数据是怎么样传输的.我们接着i2c_probe()往下看.如果i2c_probe_address()成功.说明总线上确实有这样的设备.那么就会调用驱动中的回调函数.在ad7148的驱动中,如下所示:return i2c_probe(adapter, &addr_data, ad7418_detect);也就是说,要调用的回调函数是ad7418_detect().这个函数中我们只分析和i2c框架相关的部份.代码片段如下所示:static int ad7418_detect(struct i2c_adapter *adapter, int address, int kind){ struct i2c_client *client; …… ……client->addr = address; client->adapter = adapter; client->driver = &ad7418_driver; i2c_set_clientdata(client, data); …… ……if ((err = i2c_attach_client(client))) goto exit_free; …… ……}结合上面关于new-style形式的驱动分析.发现这里走的是同一个套路,即初始化了client.然后调用i2c_attach_client().后面的流程就跟上面分析的一样了.只不过,不相同的是,这里clinet已经指定了驱动为ad7418_driver.应该在注册clinet->dev之后,就不会走bus->match和bus->probe的流程了.联系朋友别欠费，天空辽阔任你飞，再多困难别后退! “
