在嵌入式中,I2C接口的意义非常重大,许多外围芯片控制接口都采用I2C。因此,了解在驱动模块中如何进行I2C总线通信是很有必要的。我们先看看I2C驱动代码的树形结构:
.
|-- Kconfig
|-- Makefile
|-- algos
| |-- Kconfig
| |-- Makefile
| |-- i2c-algo-bit.c
| |-- i2c-algo-pca.c
| |-- i2c-algo-pcf.c
| `-- i2c-algo-pcf.h
|-- busses
| |-- Kconfig
| |-- Makefile
| |-- i2c-acorn.c
| |-- ...
| |-- i2c-gpio.c
| |-- ...
| |-- i2c-pxa.c
| |-- i2c-s3c2410.c
| `-- ...
|-- chips
| |-- Kconfig
| |-- Makefile
| |-- ds1682.c
| |-- pca963x.c
| `-- tsl2550.c
|-- i2c-boardinfo.c
|-- i2c-core.c
|-- i2c-core.h
`-- i2c-dev.c
3 directories, 86 files
其中i2c-core.c是I2C核心部分,提供接口函数,i2c_adapter和i2c_driver在模块初始化时分别调用i2c_add_numbered_adapter()和i2c_add_driver()将其注册到I2C Core中。
i2c-dev.c是I2C设备部分,实现字符设备访问接口,对硬件的具体访问是通过i2c_adapter来实现的。它在初始化时,需要向I2C Core注册一个i2c_driver。我认为这部分仅仅是让用户层访问I2C总线的,如果内核态访问I2C总线的话,则没有必要理会它;但是我们需要参考它来实现我们自己的i2c_driver,并且需要将这个i2c_driver注册到I2C Core。
busses目录下有许多个文件,为各种平台的I2C总线驱动,如s2c2410、pxa、mpc等等,跟硬件spec息息相关。一个总线驱动需要两个模块,用结构体i2c_adapter和i2c_algorithm来描述。
algos目录是对bus中的i2c_algorithm的补充,特别的i2c_algorithm可在这里实现。chips是I2C Slave芯片驱动代码,如I2C控制接口的eeprom、LED段码显示芯片等。
下面是正题,附上示范代码,碰到相关场合,直接将其复制过去使用即可。
然后在模块初始化的时候调用azure_add_i2c_device()即将一个i2c_driver注册到I2C Core,之后便可调用i2c_master_recv()和i2c_master_send()进行I2C总线读写操作。i2c_master_send()/i2c_master_recv()第一个参数client由azure_i2c传入。
- #define AZURE_I2C_ADDR 0x1a
- #define AZURE_I2C_BUS_NO 0
- static struct i2c_client *azure_i2c;
- static int azure_i2c_probe(struct i2c_client *i2c,
- const struct i2c_device_id *id)
- {
- azure_i2c = i2c;
- i2c->addr = AZURE_I2C_ADDR;
- return 0;
- }
- static int azure_i2c_remove(struct i2c_client *client)
- {
- return 0;
- }
- static const struct i2c_device_id azure_i2c_id[] = {
- { "azure", 0 },
- { }
- };
- MODULE_DEVICE_TABLE(i2c, azure_i2c_id);
- static struct i2c_driver azure_i2c_driver = {
- .driver = {
- .name = "AZURE I2C",
- .owner = THIS_MODULE,
- },
- .probe = azure_i2c_probe,
- .remove = azure_i2c_remove,
- .id_table = azure_i2c_id,
- };
- static int azure_add_i2c_device()
- {
- struct i2c_board_info info;
- struct i2c_adapter *adapter;
- struct i2c_client *client;
- int ret;
- memset(&info, 0, sizeof(struct i2c_board_info));
- info.addr = AZURE_I2C_ADDR;
- strlcpy(info.type, "azure", I2C_NAME_SIZE);
- adapter = i2c_get_adapter(AZURE_I2C_BUS_NO);
- if (!adapter) {
- printk(KERN_ERR "can't get i2c adapter %d\n", AZURE_I2C_BUS_NO);
- goto err_driver;
- }
- client = i2c_new_device(adapter, &info);
- i2c_put_adapter(adapter);
- if (!client) {
- printk(KERN_ERR "can't add i2c device at 0x%x\n", (unsigned int)info.addr);
- goto err_driver;
- }
- ret = i2c_add_driver(&azure_i2c_driver);
- if (ret != 0) {
- printk(KERN_ERR "can't add i2c driver\n");
- return ret;
- }
- return 0;
- err_driver:
- i2c_del_driver(&azure_i2c_driver);
- return -ENODEV;
- }
--------------------------------------------------------------------------------
以上并不是聪明的做法。如果有N个模块要用到I2C,那么在N个模块就要添加基本一样的代码。更好的解决方法是为内核调用I2C写一个独立的模块,EXPORT_SYMBOL读写接口函数,在其他模块里就只需要调用这些读写接口函数就可以了。如下是模块代码:
- #include <linux/kernel.h>
- #include <linux/module.h>
- #include <linux/init.h>
- #include <linux/errno.h>
- #include <linux/init.h>
- #include <linux/list.h>
- #include <linux/i2c.h>
- #include <linux/smp_lock.h>
- #define I2C_API_FAKE_ADDR 0x7f
- #define I2C_MINORS 256
- int i2c_api_attach(struct i2c_adapter *adapter);
- int i2c_api_detach(struct i2c_adapter *adapter);
- struct i2c_api {
- struct list_head list;
- struct i2c_client *client;
- };
- static LIST_HEAD(i2c_api_list);
- static DEFINE_SPINLOCK(i2c_api_list_lock);
- static const unsigned short normal_addr[] = { I2C_API_FAKE_ADDR, I2C_CLIENT_END };
- static const unsigned short ignore[] = { I2C_CLIENT_END };
- static struct i2c_client_address_data addr_data =
- {
- .normal_i2c = normal_addr,
- .probe = ignore,
- .ignore = ignore,
- .forces = NULL,
- };
- static const struct i2c_device_id id[] = {
- {"I2C-API", 0},
- {}
- };
- MODULE_DEVICE_TABLE(i2c, id);
- static struct i2c_driver i2c_api_driver = {
- .id_table = id,
- .attach_adapter = i2c_api_attach,
- .detach_adapter = i2c_api_detach,
- .command = NULL,
- .driver = {
- .name = "I2C-API",
- .owner = THIS_MODULE,
- },
- .address_data = &addr_data,
- };
- static struct i2c_api *get_i2c_api(int bus_id)
- {
- struct i2c_api *i2c_api;
- spin_lock(&i2c_api_list_lock);
- list_for_each_entry(i2c_api, &i2c_api_list, list) {
- if (i2c_api->client->adapter->nr == bus_id)
- goto found;
- }
- i2c_api = NULL;
- found:
- spin_unlock(&i2c_api_list_lock);
- return i2c_api;
- }
- static struct i2c_api *add_i2c_api(struct i2c_client *client)
- {
- struct i2c_api *i2c_api;
- if (client->adapter->nr >= I2C_MINORS) {
- printk(KERN_ERR "i2c_api: Out of device minors (%d)\n",
- client->adapter->nr);
- return NULL;
- }
- i2c_api = kzalloc(sizeof(*i2c_api), GFP_KERNEL);
- if (!i2c_api)
- return NULL;
- i2c_api->client = client;
- spin_lock(&i2c_api_list_lock);
- list_add_tail(&i2c_api->list, &i2c_api_list);
- spin_unlock(&i2c_api_list_lock);
- return i2c_api;
- }
- static void del_i2c_api(struct i2c_api *i2c_api)
- {
- spin_lock(&i2c_api_list_lock);
- list_del(&i2c_api->list);
- spin_unlock(&i2c_api_list_lock);
- kfree(i2c_api);
- }
- static int i2c_api_do_xfer(int bus_id, char chip_addr, char sub_addr, int mode,
- char *buf, unsigned int size)
- {
- /**
- * you can define more transfer mode here, implement it below.
- */
- #define I2C_API_XFER_MODE_SEND 0x0 /* standard send */
- #define I2C_API_XFER_MODE_RECV 0x1 /* standard receive */
- #define I2C_API_XFER_MODE_SEND_NO_SUBADDR 0x2 /* send with no sub address */
- #define I2C_API_XFER_MODE_RECV_NO_SUBADDR 0x3 /* receive with no sub address */
- int ret = 0;
- char *tmp;
- struct i2c_api *i2c_api = get_i2c_api(bus_id);
- if (!i2c_api)
- return -ENODEV;
- i2c_api->client->addr = chip_addr;
- switch (mode) {
- case I2C_API_XFER_MODE_SEND:
- tmp = kmalloc(size + 1,GFP_KERNEL);
- if (tmp == NULL)
- return -ENOMEM;
- tmp[0] = sub_addr;
- memcpy(&tmp[1], buf, size);
- ret = i2c_master_send(i2c_api->client, tmp, size + 1);
- ret = (ret == size + 1) ? size : ret;
- break;
-
- case I2C_API_XFER_MODE_RECV:
- ret = i2c_master_send(i2c_api->client, &sub_addr, 1);
- if (ret < 0)
- return ret;
- ret = i2c_master_recv(i2c_api->client, buf, size);
- break;
- case I2C_API_XFER_MODE_SEND_NO_SUBADDR:
- ret = i2c_master_send(i2c_api->client, buf, size);
- break;
-
- case I2C_API_XFER_MODE_RECV_NO_SUBADDR:
- ret = i2c_master_recv(i2c_api->client, buf, size);
- break;
-
- default:
- return -EINVAL;
- }
- return ret;
- }
- int i2c_api_do_send(int bus_id, char chip_addr, char sub_addr, char *buf, unsigned int size)
- {
- return i2c_api_do_xfer(bus_id, chip_addr, sub_addr, I2C_API_XFER_MODE_SEND, buf, size);
- }
- int i2c_api_do_recv(int bus_id, char chip_addr, char sub_addr, char *buf, unsigned int size)
- {
- return i2c_api_do_xfer(bus_id, chip_addr, sub_addr, I2C_API_XFER_MODE_RECV, buf, size);
- }
- int i2c_api_attach(struct i2c_adapter *adap)
- {
- struct i2c_board_info info;
- struct i2c_client *client;
- memset(&info, 0, sizeof(struct i2c_board_info));
- strlcpy(info.type, "i2c_api", I2C_NAME_SIZE);
- info.addr = I2C_API_FAKE_ADDR;
- client = i2c_new_device(adap, &info);
- if (client)
- add_i2c_api(client);
- printk(KERN_INFO "i2c_api_attach adap[%d]\n", adap->nr);
- return 0;
- }
- int i2c_api_detach(struct i2c_adapter *adap)
- {
- struct i2c_api *i2c_api;
- i2c_api = get_i2c_api(adap->nr);
- if (i2c_api)
- del_i2c_api(i2c_api);
- return 0;
- }
- static int __init i2c_api_init(void)
- {
- int ret = i2c_add_driver(&i2c_api_driver);
- if (ret) {
- printk(KERN_ERR "[%s] Driver registration failed, module not inserted.\n", __func__);
- return ret;
- }
- return 0 ;
- }
- static void __exit i2c_api_exit(void)
- {
- i2c_del_driver(&i2c_api_driver);
- }
- MODULE_AUTHOR("Loon, ");
- MODULE_DESCRIPTION("I2C i2c_api Driver");
- MODULE_LICENSE("GPL");
- module_init(i2c_api_init);
- module_exit(i2c_api_exit);
- EXPORT_SYMBOL_GPL(i2c_api_do_send);
- EXPORT_SYMBOL_GPL(i2c_api_do_recv);
内核版本是2.6.32,i2c_driver结构体成员attach_adapter和detach_adapter可能以后有增删,届时需要对模块里的i2c_api_attach()和i2c_api_detach()做调整。
加载该模块后,其他模块即可调用i2c_api_do_recv()/i2c_api_do_send()读写I2C总线。
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