I2C核心中的主要函數如下:
（1） 增加/刪除i2c_adapter
int i2c_add_adapter(struct i2c_adapter *adap);
void i2c_del_adapter(struct i2c_adapter *adap);
增加一個adadptor
/**
* i2c_add_adapter - declare i2c adapter, use dynamic bus number
* @adapter: the adapter to add
* Context: can sleep
*
* This routine is used to declare an I2C adapter when its bus number
* doesn't matter. Examples: for I2C adapters dynamically added by
* USB links or PCI plugin cards.
*
* When this returns zero, a new bus number was allocated and stored
* in adap->nr, and the specified adapter became available for clients.
* Otherwise, a negative errno value is returned.
*/
int i2c_add_adapter(struct i2c_adapter *adapter)
{
int id, res = 0;
retry:
/* 調用idr_pre_get()爲i2c_adapter預留內存空間 */
if (idr_pre_get(&i2c_adapter_idr, GFP_KERNEL) == 0)
return -ENOMEM;
mutex_lock(&core_lock);
/* "above" here means "above or equal to", sigh */
/* 調用idr_get_new_above()將結構插入i2c_adapter_idr中,並將插入的位置賦給id,以後可以通過id在i2c_adapter_idr中找到相應的i2c_adapter結構體 */
res = idr_get_new_above(&i2c_adapter_idr, adapter,
__i2c_first_dynamic_bus_num, &id);
mutex_unlock(&core_lock);
if (res < 0) {
if (res == -EAGAIN)
goto retry;
return res;
}
adapter->nr = id;
/* 調用i2c_register_adapter()函數進一步來註冊 */
return i2c_register_adapter(adapter);
}
static int i2c_register_adapter(struct i2c_adapter *adap)
{
int res = 0, dummy;
/* Can't register until after driver model init */
if (unlikely(WARN_ON(!i2c_bus_type.p))) {
res = -EAGAIN;
goto out_list;
}
/* 初始化adaptor的參數*/
rt_mutex_init(&adap->bus_lock);
INIT_LIST_HEAD(&adap->userspace_clients);
/* Set default timeout to 1 second if not already set */
if (adap->timeout == 0)
adap->timeout = HZ;
dev_set_name(&adap->dev, "i2c-%d", adap->nr);
adap->dev.bus = &i2c_bus_type;
adap->dev.type = &i2c_adapter_type;
res = device_register(&adap->dev);
if (res)
goto out_list;
dev_dbg(&adap->dev, "adapter [%s] registered\n", adap->name);
#ifdef CONFIG_I2C_COMPAT
res = class_compat_create_link(i2c_adapter_compat_class, &adap->dev,
adap->dev.parent);
if (res)
dev_warn(&adap->dev,
"Failed to create compatibility class link\n");
#endif
/* create pre-declared device nodes */
/* 註冊所有在板文件裏定義的設備 */
if (adap->nr < __i2c_first_dynamic_bus_num)
i2c_scan_static_board_info(adap);
/* Notify drivers */
mutex_lock(&core_lock);
/* 遍歷IIC總線上的所有已經註冊了的驅動
* 每找到一個就調用__process_new_adapter函數進行處理，相對後面一點位置分析
*/
dummy = bus_for_each_drv(&i2c_bus_type, NULL, adap,
__process_new_adapter);
mutex_unlock(&core_lock);
return 0;
out_list:
mutex_lock(&core_lock);
idr_remove(&i2c_adapter_idr, adap->nr);
mutex_unlock(&core_lock);
return res;
}
static void i2c_scan_static_board_info(struct i2c_adapter *adapter)
{
struct i2c_devinfo *devinfo;
down_read(&__i2c_board_lock);
/* 遍歷__i2c_board_list鏈表，每找到一個成員就調用i2c_new_device函數創建一個IIC從機設備 */
list_for_each_entry(devinfo, &__i2c_board_list, list) {
if (devinfo->busnum == adapter->nr
&& !i2c_new_device(adapter,
&devinfo->board_info))
dev_err(&adapter->dev,
"Can't create device at 0x%02x\n",
devinfo->board_info.addr);
}
up_read(&__i2c_board_lock);
}
/**
* i2c_new_device - instantiate an i2c device
* @adap: the adapter managing the device
* @info: describes one I2C device; bus_num is ignored
* Context: can sleep
*
* Create an i2c device. Binding is handled through driver model
* probe()/remove() methods. A driver may be bound to this device when we
* return from this function, or any later moment (e.g. maybe hotplugging will
* load the driver module). This call is not appropriate for use by mainboard
* initialization logic, which usually runs during an arch_initcall() long
* before any i2c_adapter could exist.
*
* This returns the new i2c client, which may be saved for later use with
* i2c_unregister_device(); or NULL to indicate an error.
*/
struct i2c_client *
i2c_new_device(struct i2c_adapter *adap, struct i2c_board_info const *info)
{
struct i2c_client *client;
int status;
/* 爲IIC從機設備結構體申請內存 */
client = kzalloc(sizeof *client, GFP_KERNEL);
if (!client)
return NULL;
/* 設備綁定總線驅動 */
client->adapter = adap;
/* 參數的綁定和初始化 */
client->dev.platform_data = info->platform_data;
if (info->archdata)
client->dev.archdata = *info->archdata;
client->flags = info->flags;
client->addr = info->addr;
client->irq = info->irq;
/* 設備名字 */
strlcpy(client->name, info->type, sizeof(client->name));
/* Check for address validity 檢查IIC從機設備地址的合法性
* 怎樣才合法？如果從機使用十位地址的話，那麼地址的最大值不能大於0x3ff；
* 如果使用的是七位地址，那麼地址的最大值不能大於0x7f，當然也不能爲0。
*/
status = i2c_check_client_addr_validity(client);
if (status) {
dev_err(&adap->dev, "Invalid %d-bit I2C address 0x%02hx\n",
client->flags & I2C_CLIENT_TEN ? 10 : 7, client->addr);
goto out_err_silent;
}
/* Check for address business */
/*
* 檢查當前IIC從機設備的地址有沒有被使用，一條IIC總線或者一個IIC適配器上可以掛多個從機設備，
* 靠設備的地址來識別不同的設備，因此一條總線上不能有兩個同樣地址的設備
*/
status = i2c_check_addr_busy(adap, client->addr);
if (status)
goto out_err;
client->dev.parent = &client->adapter->dev; /* 一個設備是掛在一個適配器上的 */
client->dev.bus = &i2c_bus_type; /* Client屬於i2c總先 */
client->dev.type = &i2c_client_type; /* */
#ifdef CONFIG_OF
client->dev.of_node = info->of_node;
#endif
/* 設備名字形式爲,適配器號-設備地址 */
dev_set_name(&client->dev, "%d-%04x", i2c_adapter_id(adap),
client->addr);
status = device_register(&client->dev); /* 註冊設備 */
if (status)
goto out_err;
dev_dbg(&adap->dev, "client [%s] registered with bus id %s\n",
client->name, dev_name(&client->dev));
return client;
out_err:
dev_err(&adap->dev, "Failed to register i2c client %s at 0x%02x "
"(%d)\n", client->name, client->addr, status);
out_err_silent:
kfree(client);
return NULL;
}
/**
* bus_for_each_drv - driver iterator
* @bus: bus we're dealing with.
* @start: driver to start iterating on.
* @data: data to pass to the callback.
* @fn: function to call for each driver.
*
* This is nearly identical to the device iterator above.
* We iterate over each driver that belongs to @bus, and call
* @fn for each. If @fn returns anything but 0, we break out
* and return it. If @start is not NULL, we use it as the head
* of the list.
*
* NOTE: we don't return the driver that returns a non-zero
* value, nor do we leave the reference count incremented for that
* driver. If the caller needs to know that info, it must set it
* in the callback. It must also be sure to increment the refcount
* so it doesn't disappear before returning to the caller.
*/
int bus_for_each_drv(struct bus_type *bus, struct device_driver *start,
void *data, int (*fn)(struct device_driver *, void *))
{
struct klist_iter i;
struct device_driver *drv;
int error = 0;
if (!bus)
return -EINVAL;
/* 用總線驅動鏈表上的每個驅動都和設備進行匹配嘗試 */
klist_iter_init_node(&bus->p->klist_drivers, &i,
start ? &start->p->knode_bus : NULL);
while ((drv = next_driver(&i)) && !error)
error = fn(drv, data);
klist_iter_exit(&i);
return error;
}
/* i2c的驅動鏈表和adaptor做匹配 */
static int __process_new_adapter(struct device_driver *d, void *data)
{
return i2c_do_add_adapter(to_i2c_driver(d), data);
}
static int i2c_do_add_adapter(struct i2c_driver *driver,
struct i2c_adapter *adap)
{
/* Detect supported devices on that bus, and instantiate them */
/* 檢查驅動是否能夠與該適配器所在總線上的設備匹配 */
i2c_detect(adap, driver);
/* Let legacy drivers scan this bus for matching devices */
/* 如果驅動的attach_adapter函數有定義就調用之，這主要針對舊的驅動,新的會移除掉的 */
if (driver->attach_adapter) {
/* We ignore the return code; if it fails, too bad */
driver->attach_adapter(adap);
}
return 0;
}
static int i2c_detect(struct i2c_adapter *adapter, struct i2c_driver *driver)
{
const unsigned short *address_list;
struct i2c_client *temp_client;
int i, err = 0;
int adap_id = i2c_adapter_id(adapter);
address_list = driver->address_list; //驅動可以支持的地址鏈表
if (!driver->detect || !address_list)
return 0;
/* Set up a temporary client to help detect callback */
/* 申請一個臨時的i2c_clinet,用來探測設備是否存在 */
temp_client = kzalloc(sizeof(struct i2c_client), GFP_KERNEL);
if (!temp_client)
return -ENOMEM;
temp_client->adapter = adapter; /* 設備綁定適配器 */
/* Stop here if the classes do not match */
if (!(adapter->class & driver->class))
goto exit_free;
/* Stop here if the bus doesn't support probing */
/* 總線是否支持探測 */
if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_READ_BYTE)) {
if (address_list[0] == I2C_CLIENT_END) /* 驅動應該是最後一項是地址的結束符 */
goto exit_free;
dev_warn(&adapter->dev, "Probing not supported\n");
err = -EOPNOTSUPP;
goto exit_free;
}
/* 使用這個驅動支持的所有地址都嘗試一下地址能否匹配 */
for (i = 0; address_list[i] != I2C_CLIENT_END; i += 1) {
dev_dbg(&adapter->dev, "found normal entry for adapter %d, "
"addr 0x%02x\n", adap_id, address_list[i]);
temp_client->addr = address_list[i];
err = i2c_detect_address(temp_client, driver);
if (err)
goto exit_free;
}
exit_free:
kfree(temp_client);
return err;
}
static int i2c_detect_address(struct i2c_client *temp_client,
struct i2c_driver *driver)
{
struct i2c_board_info info;
struct i2c_adapter *adapter = temp_client->adapter;
int addr = temp_client->addr;
int err;
/* Make sure the address is valid */
err = i2c_check_addr_validity(addr); //檢查地址有效
if (err) {
dev_warn(&adapter->dev, "Invalid probe address 0x%02x\n",
addr);
return err;
}
/* Skip if already in use */
if (i2c_check_addr_busy(adapter, addr)) //檢查這個adaptor上,是不是已經有這個地址的設備了
return 0;
/* Make sure there is something at this address */
if (!i2c_default_probe(adapter, addr)) //使用默認檢測這個設備存在
return 0;
/* Finally call the custom detection function */
memset(&info, 0, sizeof(struct i2c_board_info));
info.addr = addr;
err = driver->detect(temp_client, &info); //調用驅動中的detect函數來進行探測
if (err) {
/* -ENODEV is returned if the detection fails. We catch it
here as this isn't an error. */
return err == -ENODEV ? 0 : err;
}
/* Consistency check */
if (info.type[0] == '\0') {
dev_err(&adapter->dev, "%s detection function provided "
"no name for 0x%x\n", driver->driver.name,
addr);
} else {
struct i2c_client *client;
/* 這個設備檢測確實有的話,則進行實例化,並把設備(client)加入到驅動鏈表上 */
/* Detection succeeded, instantiate the device */
dev_dbg(&adapter->dev, "Creating %s at 0x%02x\n",
info.type, info.addr);
client = i2c_new_device(adapter, &info);
if (client)
list_add_tail(&client->detected, &driver->clients);
else
dev_err(&adapter->dev, "Failed creating %s at 0x%02x\n",
info.type, info.addr);
}
return 0;
}
刪除一個adaptor
/**
* i2c_del_adapter - unregister I2C adapter
* @adap: the adapter being unregistered
* Context: can sleep
*
* This unregisters an I2C adapter which was previously registered
* by @i2c_add_adapter or @i2c_add_numbered_adapter.
*/
int i2c_del_adapter(struct i2c_adapter *adap)
{
int res = 0;
struct i2c_adapter *found;
struct i2c_client *client, *next;
/* First make sure that this adapter was ever added */
/* 通過adaptor中的nr,找到idr中的i2c_adapter(這裏只是確認idr中確實有) */
mutex_lock(&core_lock);
found = idr_find(&i2c_adapter_idr, adap->nr);
mutex_unlock(&core_lock);
if (found != adap) {
pr_debug("i2c-core: attempting to delete unregistered "
"adapter [%s]\n", adap->name);
return -EINVAL;
}
/* Tell drivers about this removal */
/* */
mutex_lock(&core_lock);
res = bus_for_each_drv(&i2c_bus_type, NULL, adap,
__process_removed_adapter);
mutex_unlock(&core_lock);
if (res)
return res;
/* Remove devices instantiated from sysfs */
i2c_lock_adapter(adap);
list_for_each_entry_safe(client, next, &adap->userspace_clients,
detected) {
dev_dbg(&adap->dev, "Removing %s at 0x%x\n", client->name,
client->addr);
list_del(&client->detected);
i2c_unregister_device(client);
}
i2c_unlock_adapter(adap);
/* Detach any active clients. This can't fail, thus we do not
checking the returned value. */
res = device_for_each_child(&adap->dev, NULL, __unregister_client);
#ifdef CONFIG_I2C_COMPAT
class_compat_remove_link(i2c_adapter_compat_class, &adap->dev,
adap->dev.parent);
#endif
/* device name is gone after device_unregister */
dev_dbg(&adap->dev, "adapter [%s] unregistered\n", adap->name);
/* clean up the sysfs representation */
init_completion(&adap->dev_released);
device_unregister(&adap->dev);
/* wait for sysfs to drop all references */
wait_for_completion(&adap->dev_released);
/* free bus id */
mutex_lock(&core_lock);
idr_remove(&i2c_adapter_idr, adap->nr);
mutex_unlock(&core_lock);
/* Clear the device structure in case this adapter is ever going to be
added again */
memset(&adap->dev, 0, sizeof(adap->dev));
return 0;
}
/**
* bus_for_each_drv - driver iterator
* @bus: bus we're dealing with.
* @start: driver to start iterating on.
* @data: data to pass to the callback.
* @fn: function to call for each driver.
*
* This is nearly identical to the device iterator above.
* We iterate over each driver that belongs to @bus, and call
* @fn for each. If @fn returns anything but 0, we break out
* and return it. If @start is not NULL, we use it as the head
* of the list.
*
* NOTE: we don't return the driver that returns a non-zero
* value, nor do we leave the reference count incremented for that
* driver. If the caller needs to know that info, it must set it
* in the callback. It must also be sure to increment the refcount
* so it doesn't disappear before returning to the caller.
*/
int bus_for_each_drv(struct bus_type *bus, struct device_driver *start,
void *data, int (*fn)(struct device_driver *, void *))
{
struct klist_iter i;
struct device_driver *drv;
int error = 0;
if (!bus)
return -EINVAL;
/* 遍歷總線上的所有driver,執行fn函數 */
klist_iter_init_node(&bus->p->klist_drivers, &i,
start ? &start->p->knode_bus : NULL);
while ((drv = next_driver(&i)) && !error)
error = fn(drv, data);
klist_iter_exit(&i);
return error;
}
static int __process_removed_adapter(struct device_driver *d, void *data)
{
return i2c_do_del_adapter(to_i2c_driver(d), data);
}
static int i2c_do_del_adapter(struct i2c_driver *driver,
struct i2c_adapter *adapter)
{
struct i2c_client *client, *_n;
int res;
/* Remove the devices we created ourselves as the result of hardware
* probing (using a driver's detect method) */
/* 因爲一個driver上可能有多個client,所以要把所有的device（client）都卸載了,再清楚adaptor */
list_for_each_entry_safe(client, _n, &driver->clients, detected) {
if (client->adapter == adapter) {
dev_dbg(&adapter->dev, "Removing %s at 0x%x\n",
client->name, client->addr);
list_del(&client->detected);
i2c_unregister_device(client);
}
}
/* 卸載adaptor */
if (!driver->detach_adapter)
return 0;
res = driver->detach_adapter(adapter);
if (res)
dev_err(&adapter->dev, "detach_adapter failed (%d) "
"for driver [%s]\n", res, driver->driver.name);
return res;
}
（2） 增加/刪除i2c_driver
int i2c_register_driver(struct module *owner, struct i2c_driver *driver);
int i2c_add_driver(struct i2c_driver *driver);
void i2c_del_driver(struct i2c_driver *);
static inline int i2c_add_driver(struct i2c_driver *driver)
{
return i2c_register_driver(THIS_MODULE, driver);
}
增加一個驅動
/*
* An i2c_driver is used with one or more i2c_client (device) nodes to access
* i2c slave chips, on a bus instance associated with some i2c_adapter.
*/
int i2c_register_driver(struct module *owner, struct i2c_driver *driver)
{
int res;
/* Can't register until after driver model init */
if (unlikely(WARN_ON(!i2c_bus_type.p)))
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; //設置總線
/* When registration returns, the driver core
* will have called probe() for all matching-but-unbound devices.
*/
/* sysfs中創建屬性,把driver綁定到總線的driver鏈表 */
res = driver_register(&driver->driver);
if (res)
return res;
pr_debug("i2c-core: driver [%s] registered\n", driver->driver.name);
/* 初始化這個驅動的設備(client)鏈表 */
INIT_LIST_HEAD(&driver->clients);
/* Walk the adapters that are already present */
/* 下面這個已經見過很多次了 */
mutex_lock(&core_lock);
bus_for_each_dev(&i2c_bus_type, NULL, driver, __process_new_driver);
mutex_unlock(&core_lock);
return 0;
}
/* 這個函數和前的也是一樣的,都是一個互相遍歷的過程 */
static int __process_new_driver(struct device *dev, void *data)
{
if (dev->type != &i2c_adapter_type)
return 0;
return i2c_do_add_adapter(data, to_i2c_adapter(dev));
}
刪除函數也很簡單，先把driver上的設備（client）卸載了，之後再把驅動卸載了
/**
* i2c_del_driver - unregister I2C driver
* @driver: the driver being unregistered
* Context: can sleep
*/
void i2c_del_driver(struct i2c_driver *driver)
{
mutex_lock(&core_lock);
bus_for_each_dev(&i2c_bus_type, NULL, driver, __process_removed_driver);
mutex_unlock(&core_lock);
driver_unregister(&driver->driver);
pr_debug("i2c-core: driver [%s] unregistered\n", driver->driver.name);
}
/* 移除驅動函數 */
static int __process_removed_driver(struct device *dev, void *data)
{
if (dev->type != &i2c_adapter_type)
return 0;
return i2c_do_del_adapter(data, to_i2c_adapter(dev));
}
這裏我們注意到一個事實，無論移除adaptor，還是driver。或者增加adaptor還是driver，遍歷底層都是調用的下面兩個函數
static int i2c_do_del_adapter(struct i2c_driver *driver,
struct i2c_adapter *adapter);
static int i2c_do_add_adapter(struct i2c_driver *driver,
struct i2c_adapter *adap);
static int __process_removed_driver(struct device *dev, void *data)
{
if (dev->type != &i2c_adapter_type)
return 0;
return i2c_do_del_adapter(data, to_i2c_adapter(dev));
}
static int __process_new_driver(struct device *dev, void *data)
{
if (dev->type != &i2c_adapter_type)
return 0;
return i2c_do_add_adapter(data, to_i2c_adapter(dev));
}
這裏我們注意到，對於設備驅動的增加還是刪除，這個data指針傳的都是driver
static int __process_new_adapter(struct device_driver *d, void *data)
{
return i2c_do_add_adapter(to_i2c_driver(d), data);
}
static int __process_removed_adapter(struct device_driver *d, void *data)
{
return i2c_do_del_adapter(to_i2c_driver(d), data);
}
這裏我們注意到，對於adaptor的增加還是刪除，這個data指針傳的都是adaptor
（3） I2C傳輸、 發送和接收
int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num);
int i2c_master_send(struct i2c_client *client, const char *buf, int count);
int i2c_master_recv(struct i2c_client *client, char *buf, int count);
這裏的主機發送和接收也是借用了傳輸函數
/**
* 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(struct i2c_client *client, const char *buf, int count)
{
int ret;
struct i2c_adapter *adap = client->adapter;
struct i2c_msg msg;
/* 對於發送函數,就是把要發送的數據整合成一個數據包,進行發送 */
msg.addr = client->addr;
msg.flags = client->flags & I2C_M_TEN;
msg.len = count;
msg.buf = (char *)buf;
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(struct i2c_client *client, char *buf, int count)
{
struct i2c_adapter *adap = client->adapter;
struct i2c_msg msg;
int ret;
/* 對於接收函數,這裏表示把接收的數據整理成一個包,這裏會設置接收數據的大小,以及存放位置 */
msg.addr = client->addr;
msg.flags = client->flags & I2C_M_TEN;
msg.flags |= I2C_M_RD;
msg.len = count;
msg.buf = buf;
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;
}
這裏會用到一些標誌，常用的就是I2C_M_RD讀數據，當然對於寫，其實就是0了，之前的協議已經看過了。
#define I2C_M_TEN 0x0010 /* this is a ten bit chip address */
#define I2C_M_RD 0x0001 /* read data, from slave to master */
#define I2C_M_NOSTART 0x4000 /* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_REV_DIR_ADDR 0x2000 /* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_IGNORE_NAK 0x1000 /* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_NO_RD_ACK 0x0800 /* if I2C_FUNC_PROTOCOL_MANGLING */
#define I2C_M_RECV_LEN 0x0400 /* length will be first received byte */
當然這裏要說一下的是內核把I2C總線和SMbus集成在一塊了，因爲兩個也確實很相似。
這裏關於smbus的內容我們就略過。
/**
* i2c_transfer - execute a single or combined I2C message
* @adap: Handle to I2C bus
* @msgs: One or more messages to execute before STOP is issued to
* terminate the operation; each message begins with a START.
* @num: Number of messages to be executed.
*
* Returns negative errno, else the number of messages executed.
*
* Note that there is no requirement that each message be sent to
* the same slave address, although that is the most common model.
*/
int i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
{
unsigned long orig_jiffies;
int ret, try;
/* 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).
*/
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
/* 這裏是如果在中斷中或中斷禁止時,是嘗試獲取鎖,不會睡眠的 */
if (in_atomic() || irqs_disabled()) {
ret = rt_mutex_trylock(&adap->bus_lock);
if (!ret)
/* I2C activity is ongoing. */
return -EAGAIN;
} else {
/* 沒在中斷,是可以任何時候睡眠的 */
rt_mutex_lock(&adap->bus_lock);
}
/* Retry automatically on arbitration loss */
/* 對於smbus,是有超時功能的,需要軟件來處理,而i2c超時後是硬件復位處理的 */
orig_jiffies = jiffies;
for (ret = 0, try = 0; try <= adap->retries; try++) {
ret = adap->algo->master_xfer(adap, msgs, num); //執行發生msg函數
if (ret != -EAGAIN)
break;
if (time_after(jiffies, orig_jiffies + adap->timeout))
break;
}
rt_mutex_unlock(&adap->bus_lock);
return ret;
} else {
dev_dbg(&adap->dev, "I2C level transfers not supported\n");
return -EOPNOTSUPP;
}
}
最後這裏要強調一個內容。就是一個adapter註冊的時候，我們忽略了一個很重要的內容。
也就是下面這兩個所謂的type，這兩個type很重要。一個是註冊總線，一個時這個總線在sys文件系統中的組織結構（attribute）
理解上面兩個都需要非常號的驅動模型基礎，之前總結過一個專欄，這裏給出。
https://blog.csdn.net/qq_16777851/column/info/30460
總線的這裏不再詳細分析，前面也有涉及。
這裏就只說這個type，有groups和release。我們主要看groups.
static struct device_type i2c_adapter_type = {
.groups = i2c_adapter_attr_groups,
.release = i2c_adapter_dev_release,
};
static const struct attribute_group *i2c_adapter_attr_groups[] = {
&i2c_adapter_attr_group,
NULL
};
static struct attribute_group i2c_adapter_attr_group = {
.attrs = i2c_adapter_attrs,
};
static struct attribute *i2c_adapter_attrs[] = {
&dev_attr_name.attr,
&dev_attr_new_device.attr,
&dev_attr_delete_device.attr,
NULL
};
之前如果學習過pwm子系統就應該知道，可以使用sys接口從用戶空間傳參來註冊一個設備。
i2c也是用的這個套路。
下面我們就看一下怎麼通過sysfs來註冊設備的。
正常我們肯定都是知道設備在系統中的那個iic控制器（adaptor）下面掛了。所以註冊的時候直接在這個iic控制器下面去創建。
sys下創建iic設備也很簡單。
在具體的adaptor下面，傳入設備名，設備地址就可以
echo eeprom 0x50 > /sys/bus/i2c/devices/i2c-3/new_device
/*
* Let users instantiate I2C devices through sysfs. This can be used when
* platform initialization code doesn't contain the proper data for
* whatever reason. Also useful for drivers that do device detection and
* detection fails, either because the device uses an unexpected address,
* or this is a compatible device with different ID register values.
*
* Parameter checking may look overzealous, but we really don't want
* the user to provide incorrect parameters.
*/
static ssize_t
i2c_sysfs_new_device(struct device *dev, struct device_attribute *attr,
const char *buf, size_t count)
{
/* 拿到這個adaptor */
struct i2c_adapter *adap = to_i2c_adapter(dev);
struct i2c_board_info info;
struct i2c_client *client;
char *blank, end;
int res;
dev_warn(dev, "The new_device interface is still experimental "
"and may change in a near future\n");
memset(&info, 0, sizeof(struct i2c_board_info));
/* 設備設備名字和設備地址之間的空格 */
blank = strchr(buf, ' ');
if (!blank) {
dev_err(dev, "%s: Missing parameters\n", "new_device");
return -EINVAL;
}
if (blank - buf > I2C_NAME_SIZE - 1) {
dev_err(dev, "%s: Invalid device name\n", "new_device");
return -EINVAL;
}
/* 設置設備名字 */
memcpy(info.type, buf, blank - buf);
/* Parse remaining parameters, reject extra parameters */
/* 解析得到設備地址 */
res = sscanf(++blank, "%hi%c", &info.addr, &end);
if (res < 1) {
dev_err(dev, "%s: Can't parse I2C address\n", "new_device");
return -EINVAL;
}
if (res > 1 && end != '\n') {
dev_err(dev, "%s: Extra parameters\n", "new_device");
return -EINVAL;
}
/* 創建一個設備 */
client = i2c_new_device(adap, &info);
if (!client)
return -EINVAL;
/* Keep track of the added device */
i2c_lock_adapter(adap);
/* 設備加入到adapter的用戶空間創建的設備鏈表中 */
list_add_tail(&client->detected, &adap->userspace_clients);
i2c_unlock_adapter(adap);
dev_info(dev, "%s: Instantiated device %s at 0x%02hx\n", "new_device",
info.type, info.addr);
return count;
}
從sysfs刪除一個設備，也很簡單，這裏就不再分析了
/*
* And of course let the users delete the devices they instantiated, if
* they got it wrong. This interface can only be used to delete devices
* instantiated by i2c_sysfs_new_device above. This guarantees that we
* don't delete devices to which some kernel code still has references.
*
* Parameter checking may look overzealous, but we really don't want
* the user to delete the wrong device.
*/
static ssize_t
i2c_sysfs_delete_device(struct device *dev, struct device_attribute *attr,
const char *buf, size_t count)
{
struct i2c_adapter *adap = to_i2c_adapter(dev);
struct i2c_client *client, *next;
unsigned short addr;
char end;
int res;
/* Parse parameters, reject extra parameters */
res = sscanf(buf, "%hi%c", &addr, &end);
if (res < 1) {
dev_err(dev, "%s: Can't parse I2C address\n", "delete_device");
return -EINVAL;
}
if (res > 1 && end != '\n') {
dev_err(dev, "%s: Extra parameters\n", "delete_device");
return -EINVAL;
}
/* Make sure the device was added through sysfs */
res = -ENOENT;
i2c_lock_adapter(adap);
list_for_each_entry_safe(client, next, &adap->userspace_clients,
detected) {
if (client->addr == addr) {
dev_info(dev, "%s: Deleting device %s at 0x%02hx\n",
"delete_device", client->name, client->addr);
list_del(&client->detected);
i2c_unregister_device(client);
res = count;
break;
}
}
i2c_unlock_adapter(adap);
if (res < 0)
dev_err(dev, "%s: Can't find device in list\n",
"delete_device");
return res;
}