I2C设备驱动要使用i2c_driver和i2c_client数据结构并填充i2c_driver中的成员函数。 i2c_client一般被包
含在设备的私有信息结构体yyy_data中， 而i2c_driver则适合被定义为全局变量并初始化
| static struct i2c_driver pca954x_driver = { .driver = { .name = "pca954x", .pm = &pca954x_pm, .of_match_table = pca954x_of_match, }, .probe = pca954x_probe, .remove = pca954x_remove, .id_table = pca954x_id, }; static const struct of_device_id pca954x_of_match[] = { { .compatible = "nxp,pca9540", .data = &chips[pca_9540] }, { .compatible = "nxp,pca9542", .data = &chips[pca_9542] }, { .compatible = "nxp,pca9543", .data = &chips[pca_9543] }, { .compatible = "nxp,pca9544", .data = &chips[pca_9544] }, { .compatible = "nxp,pca9545", .data = &chips[pca_9545] }, { .compatible = "nxp,pca9546", .data = &chips[pca_9546] }, { .compatible = "nxp,pca9547", .data = &chips[pca_9547] }, { .compatible = "nxp,pca9548", .data = &chips[pca_9548] }, { .compatible = "nxp,pca9846", .data = &chips[pca_9846] }, { .compatible = "nxp,pca9847", .data = &chips[pca_9847] }, { .compatible = "nxp,pca9848", .data = &chips[pca_9848] }, { .compatible = "nxp,pca9849", .data = &chips[pca_9849] }, {} }; static const struct i2c_device_id pca954x_id[] = { { "pca9540", pca_9540 }, { "pca9542", pca_9542 }, { "pca9543", pca_9543 }, { "pca9544", pca_9544 }, { "pca9545", pca_9545 }, { "pca9546", pca_9546 }, { "pca9547", pca_9547 }, { "pca9548", pca_9548 }, { "pca9846", pca_9846 }, { "pca9847", pca_9847 }, { "pca9848", pca_9848 }, { "pca9849", pca_9849 }, { } }; |
I2C设备驱动的模块加载函数通过I2C核心的i2c_add_driver（） API函数添加i2c_driver的工作
| #define i2c_add_driver(driver) \ i2c_register_driver(THIS_MODULE, driver)
{ int res; /* Can't register until after driver model init */ if (WARN_ON(!is_registered)) return -EAGAIN; /* add the driver to the list of i2c drivers in the driver core */ driver->driver.owner = owner; driver->driver.bus = &i2c_bus_type; INIT_LIST_HEAD(&driver->clients); /* When registration returns, the driver core * will have called probe() for all matching-but-unbound devices. */ res = driver_register(&driver->driver); if (res) return res; pr_debug("driver [%s] registered\n", driver->driver.name); /* Walk the adapters that are already present */ i2c_for_each_dev(driver, __process_new_driver); return 0; } |
模块卸载函数需要做相反的工作： 通过I2C核心的i2c_del_driver（） 函数删除i2c_driver。
| void i2c_del_driver(struct i2c_driver *driver) { i2c_for_each_dev(driver, __process_removed_driver); driver_unregister(&driver->driver); pr_debug("driver [%s] unregistered\n", driver->driver.name); } |
I2C设备驱动的数据传输
在I2C设备上读写数据的时序且数据通常通过i2c_msg数组进行组织， 最后通过i2c_transfer（） 函数完成
i2c-core-acpi.c
read
| static int acpi_gsb_i2c_read_bytes(struct i2c_client *client, u8 cmd, u8 *data, u8 data_len) { struct i2c_msg msgs[2]; int ret; u8 *buffer; buffer = kzalloc(data_len, GFP_KERNEL); if (!buffer) return AE_NO_MEMORY; msgs[0].addr = client->addr; msgs[0].flags = client->flags; msgs[0].len = 1; msgs[0].buf = &cmd; msgs[1].addr = client->addr; msgs[1].flags = client->flags | I2C_M_RD; msgs[1].len = data_len; msgs[1].buf = buffer; ret = i2c_transfer(client->adapter, msgs, ARRAY_SIZE(msgs)); if (ret < 0) { /* Getting a NACK is unfortunately normal with some DSTDs */ if (ret == -EREMOTEIO) dev_dbg(&client->adapter->dev, "i2c read %d bytes from client@%#x starting at reg %#x failed, error: %d\n", data_len, client->addr, cmd, ret); else dev_err(&client->adapter->dev, "i2c read %d bytes from client@%#x starting at reg %#x failed, error: %d\n", data_len, client->addr, cmd, ret); /* 2 transfers must have completed successfully */ } else if (ret == 2) { memcpy(data, buffer, data_len); ret = 0; } else { ret = -EIO; } kfree(buffer); return ret; } |
write
| static int acpi_gsb_i2c_write_bytes(struct i2c_client *client, u8 cmd, u8 *data, u8 data_len) { struct i2c_msg msgs[1]; u8 *buffer; int ret = AE_OK; buffer = kzalloc(data_len + 1, GFP_KERNEL); if (!buffer) return AE_NO_MEMORY; buffer[0] = cmd; memcpy(buffer + 1, data, data_len); msgs[0].addr = client->addr; msgs[0].flags = client->flags; msgs[0].len = data_len + 1; msgs[0].buf = buffer; ret = i2c_transfer(client->adapter, msgs, ARRAY_SIZE(msgs)); kfree(buffer); if (ret < 0) { dev_err(&client->adapter->dev, "i2c write failed: %d\n", ret); return ret; } /* 1 transfer must have completed successfully */ return (ret == 1) ? 0 : -EIO; } |
transfer
| int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num) { int ret; if (!adap->algo->master_xfer) { dev_dbg(&adap->dev, "I2C level transfers not supported\n"); return -EOPNOTSUPP; } /* REVISIT the fault reporting model here is weak: * * - When we get an error after receiving N bytes from a slave, * there is no way to report "N". * * - When we get a NAK after transmitting N bytes to a slave, * there is no way to report "N" ... or to let the master * continue executing the rest of this combined message, if * that's the appropriate response. * * - When for example "num" is two and we successfully complete * the first message but get an error part way through the * second, it's unclear whether that should be reported as * one (discarding status on the second message) or errno * (discarding status on the first one). */ ret = __i2c_lock_bus_helper(adap); if (ret) return ret; ret = __i2c_transfer(adap, msgs, num); i2c_unlock_bus(adap, I2C_LOCK_SEGMENT); return ret; } int __i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num) { unsigned long orig_jiffies; int ret, try; if (WARN_ON(!msgs || num < 1)) return -EINVAL; ret = __i2c_check_suspended(adap); if (ret) return ret; if (adap->quirks && i2c_check_for_quirks(adap, msgs, num)) return -EOPNOTSUPP; /* * i2c_trace_msg_key gets enabled when tracepoint i2c_transfer gets * enabled. This is an efficient way of keeping the for-loop from * being executed when not needed. */ if (static_branch_unlikely(&i2c_trace_msg_key)) { int i; for (i = 0; i < num; i++) if (msgs[i].flags & I2C_M_RD) trace_i2c_read(adap, &msgs[i], i); else trace_i2c_write(adap, &msgs[i], i); } /* Retry automatically on arbitration loss */ orig_jiffies = jiffies; for (ret = 0, try = 0; try <= adap->retries; try++) { if (i2c_in_atomic_xfer_mode() && adap->algo->master_xfer_atomic) ret = adap->algo->master_xfer_atomic(adap, msgs, num); else ret = adap->algo->master_xfer(adap, msgs, num); if (ret != -EAGAIN) break; if (time_after(jiffies, orig_jiffies + adap->timeout)) break; } if (static_branch_unlikely(&i2c_trace_msg_key)) { int i; for (i = 0; i < ret; i++) if (msgs[i].flags & I2C_M_RD) trace_i2c_reply(adap, &msgs[i], i); trace_i2c_result(adap, num, ret); } return ret; } |
