linux驅動--i2c驅動學習
預備知識
在閱讀本文最好先熟悉一種i2c裝置的驅動程式,並且瀏覽一下i2c-core.c以及晶片提供商的提供的i2c匯流排驅動(i2c-davinci.c)。標題黨請見諒!
其實i2c介面非常的簡單,即使用51單片的gpio來模擬i2c,編寫一個e2prom或者其他i2c介面的驅動程式,也不是什麼難事,幾百行程式碼就能搞定。
但是Linux的i2c驅動體系結構卻有相當的複雜度,不管是叫linux i2c驅動還是微控制器i2c驅動,其根本還是操作soc晶片內部的i2c模組(也叫i2c adapter)(讀寫i2c相關的暫存器)來產生start、stop還有ack訊號而已。
linux裝置驅動到底複雜在什麼地方?
假設soc晶片dm368有兩個i2c adapter(368內部真正只有一個i2c模組):i2c_adapter1,i2c_adapter1;然後外部有三個i2c介面的裝置i2c_device1,i2c_device2,i2c_device3。
現在要求在裸機下寫出他們的驅動函式。那麼肯定要寫出6個不同的驅動函式:
[cpp] view plaincopyprint?- i2c_adapter1_ReadWrite_i2c_device1();
- i2c_adapter1_ReadWrite_i2c_device2()
- i2c_adapter1_ReadWrite_i2c_device3()
- i2c_adapter2_ReadWrite_i2c_device1()
- i2c_adapter2_ReadWrite_i2c_device2()
- i2c_adapter2_ReadWrite_i2c_device3()
設想一共有m個i2c adapter和n個外設i2c device,那麼將需要m*n個驅動。並且這m*n個驅動程式必要會有很大部分重複的程式碼,而且不利於驅動程式的移植。i2c_adapter1_ReadWrite_i2c_device1(); i2c_adapter1_ReadWrite_i2c_device2() i2c_adapter1_ReadWrite_i2c_device3() i2c_adapter2_ReadWrite_i2c_device1() i2c_adapter2_ReadWrite_i2c_device2() i2c_adapter2_ReadWrite_i2c_device3()
如果採用adapter和device分離的思想來寫這樣的驅動會是怎樣呢?
圖1
這樣分離之後,只需要m+n個驅動,而且Adapter和Device的幾乎沒有耦合性,增加一個Adapter或者device並不會影響其餘的驅動。
這就是分離思想帶來的好處。除此之外,linux雖然是C寫的,但是大量使用了面向物件的程式設計方法(可以理解為分層的思想),
僅僅分離細想和分層思想的引入,就大大增加了linux裝置驅動的複雜度。
linux驅動中 i2c驅動架構
圖2
上圖完整的描述了linux i2c驅動架構,雖然I2C硬體體系結構比較簡單,但是i2c體系結構在linux中的實現卻相當複雜。那麼我們如何編寫特定i2c介面器件(比如,ov2715,需要i2c來配置暫存器)的驅動程式?就是說上述架構中的那些部分需要我們完成,而哪些是linux核心已經完善的或者是晶片提供商(TI davinci平臺已經做好的)已經提供的?
架構層次分類
第一層:提供i2c adapter的硬體驅動,探測、初始化i2c adapter(如申請i2c的io地址和中斷號),驅動soc控制的i2c adapter在硬體上產生訊號(start、stop、ack)以及處理i2c中斷。覆蓋圖中的硬體實現層
第二層:提供i2c adapter的algorithm,用具體介面卡的xxx_xferf()函式來填充i2c_algorithm的master_xfer函式指標,並把賦值後的i2c_algorithm再賦值給i2c_adapter的algo指標。覆蓋圖中的訪問抽象層、i2c核心層
第三層:實現i2c裝置驅動中的i2c_driver介面,用具體的i2c device裝置的attach_adapter()、detach_adapter()方法賦值給i2c_driver的成員函式指標。實現裝置device與匯流排(或者叫adapter)的掛接。覆蓋圖中的driver驅動層
第四層:實現i2c裝置所對應的具體device的驅動,i2c_driver只是實現裝置與匯流排的掛接,而掛接在總線上的裝置則是千差萬別的,eeprom和ov2715顯然不是同一類的device,所以要實現具體裝置device的write()、read()、ioctl()等方法,賦值給file_operations,然後註冊字元裝置(多數是字元裝置)。覆蓋圖中的driver驅動層
第一層和第二層又叫i2c匯流排驅動(bus),第三第四屬於i2c裝置驅動(device driver)。在linux驅動架構中,幾乎不需要驅動開發人員再新增bus,因為linux核心幾乎整合所有匯流排bus,如usb、pci、i2c等等。並且匯流排bus中的【與特定硬體相關的程式碼】已由晶片提供商編寫完成,例如TI davinci平臺i2c匯流排bus與硬體相關的程式碼在核心目錄/drivers/i2c/buses下的i2c-davinci.c原始檔中;而三星的s3c-2440平臺i2c匯流排bus為/drivers/i2c/buses/i2c-s3c2410.c
第三第四層又叫裝置驅動層與特定device相干的就需要驅動工程師來實現了。
明確了方向後,再來具體分析。
具體分析
i2c_adapter與i2c_client的關係與i2c硬體體系中設配器與裝置的關係一致,即i2c_client依附於i2c_adapter,由於一個介面卡上可以連線多個i2c裝置device,所以相應的,i2c_adapter也可以被多個i2c_client依附,在i2c_adapter中包含i2c_client的連結串列。同一類的i2c裝置device對應一個驅動driver。driver與device的關係是一對多的關係。
現在,我們就來看一下這幾個重要的結構體,分別是i2c_driver i2c_client i2c_adapter,也可以先忽略他們,待會回過頭來看會更容易理解
1、i2c_driver
[cpp] view plaincopyprint?- struct i2c_driver {
- int id;
- unsigned intclass;
- int (*attach_adapter)(struct i2c_adapter *);
- int (*detach_adapter)(struct i2c_adapter *);
- int (*detach_client)(struct i2c_client *);
- int (*command)(struct i2c_client *client,unsigned int cmd, void *arg);
- struct device_driver driver;
- struct list_head list;
- };
struct i2c_driver {
int id;
unsigned int class;
int (*attach_adapter)(struct i2c_adapter *);
int (*detach_adapter)(struct i2c_adapter *);
int (*detach_client)(struct i2c_client *);
int (*command)(struct i2c_client *client,unsigned int cmd, void *arg);
struct device_driver driver;
struct list_head list;
};
2、i2c_client
[cpp] view plaincopyprint?- struct i2c_client {
- unsigned int flags; /* div., see below */
- unsigned short addr; /* chip address - NOTE: 7bit */
- /* addresses are stored in the */
- /* _LOWER_ 7 bits */
- struct i2c_adapter *adapter; /* the adapter we sit on */
- struct i2c_driver *driver; /* and our access routines */
- int usage_count; /* How many accesses currently */
- /* to the client */
- struct device dev; /* the device structure */
- struct list_head list;
- char name[I2C_NAME_SIZE];
- struct completion released;
- };
struct i2c_client {
unsigned int flags; /* div., see below */
unsigned short addr; /* chip address - NOTE: 7bit */
/* addresses are stored in the */
/* _LOWER_ 7 bits */
struct i2c_adapter *adapter; /* the adapter we sit on */
struct i2c_driver *driver; /* and our access routines */
int usage_count; /* How many accesses currently */
/* to the client */
struct device dev; /* the device structure */
struct list_head list;
char name[I2C_NAME_SIZE];
struct completion released;
};
3、i2c_adapter
[cpp] view plaincopyprint?- struct i2c_adapter {
- struct module *owner;
- unsigned int id;
- unsigned intclass;
- struct i2c_algorithm *algo;/* the algorithm to access the bus */
- void *algo_data;
- /* --- administration stuff. */
- int (*client_register)(struct i2c_client *);
- int (*client_unregister)(struct i2c_client *);
- /* data fields that are valid for all devices */
- struct mutex bus_lock;
- struct mutex clist_lock;
- int timeout;
- int retries;
- struct device dev; /* the adapter device */
- struct class_device class_dev; /* the class device */
- int nr;
- struct list_head clients;
- struct list_head list;
- char name[I2C_NAME_SIZE];
- struct completion dev_released;
- struct completion class_dev_released;
- };
struct i2c_adapter {
struct module *owner;
unsigned int id;
unsigned int class;
struct i2c_algorithm *algo;/* the algorithm to access the bus */
void *algo_data;
/* --- administration stuff. */
int (*client_register)(struct i2c_client *);
int (*client_unregister)(struct i2c_client *);
/* data fields that are valid for all devices */
struct mutex bus_lock;
struct mutex clist_lock;
int timeout;
int retries;
struct device dev; /* the adapter device */
struct class_device class_dev; /* the class device */
int nr;
struct list_head clients;
struct list_head list;
char name[I2C_NAME_SIZE];
struct completion dev_released;
struct completion class_dev_released;
};
4、i2c_algorithm
[cpp] view plaincopyprint?- struct i2c_algorithm {
- int (*master_xfer)(struct i2c_adapter *adap,struct i2c_msg *msgs,
- int num);
- int (*slave_send)(struct i2c_adapter *,char*,int);
- int (*slave_recv)(struct i2c_adapter *,char*,int);
- u32 (*functionality) (struct i2c_adapter *);
- };
struct i2c_algorithm {
int (*master_xfer)(struct i2c_adapter *adap,struct i2c_msg *msgs,
int num);
int (*slave_send)(struct i2c_adapter *,char*,int);
int (*slave_recv)(struct i2c_adapter *,char*,int);
u32 (*functionality) (struct i2c_adapter *);
};
【i2c_adapter與i2c_algorithm】
i2c_adapter對應與物理上的一個介面卡,而i2c_algorithm對應一套通訊方法,一個i2c介面卡需要i2c_algorithm中提供的(i2c_algorithm中的又是更下層與硬體相關的程式碼提供)通訊函式來控制介面卡上產生特定的訪問週期。缺少i2c_algorithm的i2c_adapter什麼也做不了,因此i2c_adapter中包含其使用i2c_algorithm的指標。
i2c_algorithm中的關鍵函式master_xfer()用於產生i2c訪問週期需要的start stop ack訊號,以i2c_msg(即i2c訊息)為單位傳送和接收通訊資料。i2c_msg也非常關鍵,呼叫驅動中的傳送接收函式需要填充該結構體
[cpp] view plaincopyprint?- /*
- * I2C Message - used for pure i2c transaction, also from /dev interface
- */
- struct i2c_msg {
- __u16 addr; /* slave address */
- __u16 flags;
- __u16 len; /* msg length */
- __u8 *buf; /* pointer to msg data */
- };
/*
* I2C Message - used for pure i2c transaction, also from /dev interface
*/
struct i2c_msg {
__u16 addr; /* slave address */
__u16 flags;
__u16 len; /* msg length */
__u8 *buf; /* pointer to msg data */
};
【i2c_driver和i2c_client】i2c_driver對應一套驅動方法,其主要函式是attach_adapter()和detach_client(),i2c_client對應真實的i2c物理裝置device,每個i2c裝置都需要一個i2c_client來描述,i2c_driver與i2c_client的關係是一對多。一個i2c_driver上可以支援多個同等型別的i2c_client.
【i2c_adapter和i2c_client】
i2c_adapter和i2c_client的關係與i2c硬體體系中介面卡和裝置的關係一致,即i2c_client依附於i2c_adapter,由於一個介面卡上可以連線多個i2c裝置,所以i2c_adapter中包含依附於它的i2c_client的連結串列。
從圖1圖2中都可以看出,linux核心對i2c架構抽象了一個叫核心層core的中介軟體,它分離了裝置驅動device driver和硬體控制的實現細節(如操作i2c的暫存器),core層不但為上面的裝置驅動提供封裝後的核心註冊函式,而且還為小面的硬體時間提供註冊介面(也就是i2c匯流排註冊介面),可以說core層起到了承上啟下的作用。
我們先看一下i2c-core為外部提供的核心函式(選取部分),i2c-core對應的原始檔為i2c-core.c,位於核心目錄/driver/i2c/i2c-core.c
[cpp] view plaincopyprint?- EXPORT_SYMBOL(i2c_add_adapter);
- EXPORT_SYMBOL(i2c_del_adapter);
- EXPORT_SYMBOL(i2c_del_driver);
- EXPORT_SYMBOL(i2c_attach_client);
- EXPORT_SYMBOL(i2c_detach_client);
- EXPORT_SYMBOL(i2c_transfer);
EXPORT_SYMBOL(i2c_add_adapter);
EXPORT_SYMBOL(i2c_del_adapter);
EXPORT_SYMBOL(i2c_del_driver);
EXPORT_SYMBOL(i2c_attach_client);
EXPORT_SYMBOL(i2c_detach_client);
EXPORT_SYMBOL(i2c_transfer);
如果看過i2c裝置驅動程式的人一定對上面幾個函式比較熟悉。
i2c_transfer()函式,i2c_transfer()函式本身並不具備驅動介面卡物理硬體完成訊息互動的能力,它只是尋找到i2c_adapter對應的i2c_algorithm,並使用i2c_algorithm的master_xfer()函式真正的驅動硬體流程,程式碼清單如下,不重要的已刪除。
[cpp] view plaincopyprint?- int i2c_transfer(struct i2c_adapter * adap, struct i2c_msg *msgs, int num)
- {
- int ret;
- if (adap->algo->master_xfer) {//如果master_xfer函式存在,則呼叫,否則返回錯誤
- ret = adap->algo->master_xfer(adap,msgs,num);//這個函式在硬體相關的程式碼中給algorithm賦值
- return ret;
- } else {
- return -ENOSYS;
- }
- }
int i2c_transfer(struct i2c_adapter * adap, struct i2c_msg *msgs, int num)
{
int ret;
if (adap->algo->master_xfer) {//如果master_xfer函式存在,則呼叫,否則返回錯誤
ret = adap->algo->master_xfer(adap,msgs,num);//這個函式在硬體相關的程式碼中給algorithm賦值
return ret;
} else {
return -ENOSYS;
}
}
當一個具體的client被偵測到並被關聯的時候,裝置和sysfs檔案將被註冊。相反的,在client被取消關聯的時候,sysfs檔案和裝置也被登出,驅動開發人員需開發i2c裝置驅動時,需要呼叫下列函式。程式清單如下[cpp] view plaincopyprint?
- int i2c_attach_client(struct i2c_client *client)
- {
- ...
- device_register(&client->dev);
- device_create_file(&client->dev, &dev_attr_client_name);
- ...
- return 0;
- }
int i2c_attach_client(struct i2c_client *client)
{
...
device_register(&client->dev);
device_create_file(&client->dev, &dev_attr_client_name);
...
return 0;
}
[cpp]
view plaincopyprint?
- int i2c_detach_client(struct i2c_client *client)
- {
- ...
- device_remove_file(&client->dev, &dev_attr_client_name);
- device_unregister(&client->dev);
- ...
- return res;
- }
int i2c_detach_client(struct i2c_client *client)
{
...
device_remove_file(&client->dev, &dev_attr_client_name);
device_unregister(&client->dev);
...
return res;
}
i2c_add_adapter()函式和i2c_del_adapter()在i2c-davinci.c中有呼叫,稍後分析[cpp] view plaincopyprint?
- /* -----
- * i2c_add_adapter is called from within the algorithm layer,
- * when a new hw adapter registers. A new device is register to be
- * available for clients.
- */
- int i2c_add_adapter(struct i2c_adapter *adap)
- {
- ...
- device_register(&adap->dev);
- device_create_file(&adap->dev, &dev_attr_name);
- ...
- /* inform drivers of new adapters */
- list_for_each(item,&drivers) {
- driver = list_entry(item, struct i2c_driver, list);
- if (driver->attach_adapter)
- /* We ignore the return code; if it fails, too bad */
- driver->attach_adapter(adap);
- }
- ...
- }
/* -----
* i2c_add_adapter is called from within the algorithm layer,
* when a new hw adapter registers. A new device is register to be
* available for clients.
*/
int i2c_add_adapter(struct i2c_adapter *adap)
{
...
device_register(&adap->dev);
device_create_file(&adap->dev, &dev_attr_name);
...
/* inform drivers of new adapters */
list_for_each(item,&drivers) {
driver = list_entry(item, struct i2c_driver, list);
if (driver->attach_adapter)
/* We ignore the return code; if it fails, too bad */
driver->attach_adapter(adap);
}
...
}
[cpp]
view plaincopyprint?
- int i2c_del_adapter(struct i2c_adapter *adap)
- {
- ...
- list_for_each(item,&drivers) {
- driver = list_entry(item, struct i2c_driver, list);
- if (driver->detach_adapter)
- if ((res = driver->detach_adapter(adap))) {
- }
- }
- ...
- list_for_each_safe(item, _n, &adap->clients) {
- client = list_entry(item, struct i2c_client, list);
- if ((res=client->driver->detach_client(client))) {
- }
- }
- ...
- device_remove_file(&adap->dev, &dev_attr_name);
- device_unregister(&adap->dev);
- }
int i2c_del_adapter(struct i2c_adapter *adap)
{
...
list_for_each(item,&drivers) {
driver = list_entry(item, struct i2c_driver, list);
if (driver->detach_adapter)
if ((res = driver->detach_adapter(adap))) {
}
}
...
list_for_each_safe(item, _n, &adap->clients) {
client = list_entry(item, struct i2c_client, list);
if ((res=client->driver->detach_client(client))) {
}
}
...
device_remove_file(&adap->dev, &dev_attr_name);
device_unregister(&adap->dev);
}
i2c-davinci.c是實現與硬體相關功能的程式碼集合,這部分是與平臺相關的,也叫做i2c匯流排驅動,這部分程式碼是這樣新增到系統中的[cpp] view plaincopyprint?
- staticstruct platform_driver davinci_i2c_driver = {
- .probe = davinci_i2c_probe,
- .remove = davinci_i2c_remove,
- .driver = {
- .name = "i2c_davinci",
- .owner = THIS_MODULE,
- },
- };
- /* I2C may be needed to bring up other drivers */
- staticint __init davinci_i2c_init_driver(void)
- {
- return platform_driver_register(&davinci_i2c_driver);
- }
- subsys_initcall(davinci_i2c_init_driver);
- staticvoid __exit davinci_i2c_exit_driver(void)
- {
- platform_driver_unregister(&davinci_i2c_driver);
- }
- module_exit(davinci_i2c_exit_driver);
static struct platform_driver davinci_i2c_driver = {
.probe = davinci_i2c_probe,
.remove = davinci_i2c_remove,
.driver = {
.name = "i2c_davinci",
.owner = THIS_MODULE,
},
};
/* I2C may be needed to bring up other drivers */
static int __init davinci_i2c_init_driver(void)
{
return platform_driver_register(&davinci_i2c_driver);
}
subsys_initcall(davinci_i2c_init_driver);
static void __exit davinci_i2c_exit_driver(void)
{
platform_driver_unregister(&davinci_i2c_driver);
}
module_exit(davinci_i2c_exit_driver);
並且,i2c介面卡控制硬體傳送接收資料的函式在這裡賦值給i2c-algorithm,i2c_davinci_xfer稍加修改就可以在裸機中控制i2c介面卡[cpp] view plaincopyprint?
- staticstruct i2c_algorithm i2c_davinci_algo = {
- .master_xfer = i2c_davinci_xfer,
- .functionality = i2c_davinci_func,
- };
static struct i2c_algorithm i2c_davinci_algo = {
.master_xfer = i2c_davinci_xfer,
.functionality = i2c_davinci_func,
};
然後在davinci_i2c_probe函式中,將i2c_davinci_algo新增到新增到algorithm系統中
[cpp]
view plaincopyprint?
- adap->algo = &i2c_davinci_algo;
adap->algo = &i2c_davinci_algo;
梳理圖
有時候程式碼比任何文字描述都來得直接,但是過多的程式碼展示反而讓人覺得枯燥。這個時候,需要一幅圖來梳理一下上面的內容,請看圖3。
圖3
好了,上面這些程式碼的展示是告訴我們,linux核心和晶片提供商為我們的的驅動程式提供了 i2c驅動的框架,以及框架底層與硬體相關的程式碼的實現。剩下的就是針對掛載在i2c兩線上的i2c裝置了device,如at24c02,例如ov2715,而編寫的具體裝置驅動了,這裡的裝置就是硬體介面外掛載的裝置,而非硬體介面本身(soc硬體介面本身的驅動可以理解為匯流排驅動)。
在理解了i2c驅動架構後,我們接下來再作兩方面的分析工作:一是具體的i2c裝置ov2715驅動原始碼分析,二是davinci平臺的i2c匯流排驅動原始碼。
ov2715裝置i2c驅動原始碼分析
ov2715為200萬的CMOS Sensor,晶片的暫存器控制通過i2c介面完成,i2c裝置地址為0x6c,暫存器地址為16位兩個位元組,暫存器值為8位一個位元組,可以理解為一般的字元裝置。
該驅動程式並非只能用於ov2715,因此原始碼中存在支援多個裝置地址的機制。
該字元裝置的用到的結構體有兩個,如下
- typedefstruct {
- int devAddr;
- struct i2c_client client; //!< Data structure containing general access routines.
- struct i2c_driver driver; //!< Data structure containing information specific to each client.
- char name[20];
- int nameSize;
- int users;
- } I2C_Obj;
typedef struct {
int devAddr;
struct i2c_client client; //!< Data structure containing general access routines.
struct i2c_driver driver; //!< Data structure containing information specific to each client.
char name[20];
int nameSize;
int users;
} I2C_Obj;
[cpp]
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- #define I2C_DEV_MAX_ADDR (0xFF)
- #define I2C_TRANSFER_BUF_SIZE_MAX (256)
- typedefstruct {
- struct cdev cdev; /* Char device structure */
- int major;
- struct semaphore semLock;
- I2C_Obj *pObj[I2C_DEV_MAX_ADDR];
- uint8_t reg[I2C_TRANSFER_BUF_SIZE_MAX];
- uint16_t reg16[I2C_TRANSFER_BUF_SIZE_MAX];
- uint8_t buffer[I2C_TRANSFER_BUF_SIZE_MAX*4];
- } I2C_Dev;
#define I2C_DEV_MAX_ADDR (0xFF)
#define I2C_TRANSFER_BUF_SIZE_MAX (256)
typedef struct {
struct cdev cdev; /* Char device structure */
int major;
struct semaphore semLock;
I2C_Obj *pObj[I2C_DEV_MAX_ADDR];
uint8_t reg[I2C_TRANSFER_BUF_SIZE_MAX];
uint16_t reg16[I2C_TRANSFER_BUF_SIZE_MAX];
uint8_t buffer[I2C_TRANSFER_BUF_SIZE_MAX*4];
} I2C_Dev;
一個I2C_Obj描述一個裝置,devAddr儲存該裝置的地址,I2C_Obj內嵌到結構體I2C_Dev,I2C_Dev管理該驅動所支援的所有裝置,儘管支援多個裝置,但i2c介面卡只有一個,因此需要一個訊號量semLock來保護該共享資源,同時只能向一個裝置讀寫資料。成員變數cdev是我們所熟知的,每個字元裝置驅動中幾乎總會有一個結構體包含它,major用於儲存該驅動的主裝置編號,reg陣列為暫存器地址為8位的暫存器地址緩衝區,reg16為暫存器地址為16的暫存器地址緩衝區。同時可以讀寫多個暫存器地址的值。buffer為讀寫的暫存器值 使用I2C_Dev構建一個全域性變數gI2C_dev,在驅動的多個地方均需要它。
下面先從字元裝置的基本框架入手,然後深入該驅動的細節部分。
首先是該字元裝置的初始化和退出函式 [cpp] view plaincopyprint?
- int I2C_devInit(void)
- {
- int result, i;
- dev_t dev = 0;
- result = alloc_chrdev_region(&dev, 0, 1, I2C_DRV_NAME);//分配字元裝置空間
- for(i=0; i<I2C_DEV_MAX_ADDR; i++)
- {
- gI2C_dev.pObj[i]=NULL;
- }
- gI2C_dev.major = MAJOR(dev);//儲存裝置主編號
- sema_init(&gI2C_dev.semLock, 1);//訊號量初始化
- cdev_init(&gI2C_dev.cdev, &gI2C_devFileOps);//使用gI2C_devFileOps初始化該字元裝置,gI2C_devFileOps見下文
- gI2C_dev.cdev.owner = THIS_MODULE;//常規賦值
- gI2C_dev.cdev.ops = &gI2C_devFileOps;//常規賦值 result = cdev_add(&gI2C_dev.cdev, dev, 1);//新增裝置到字元裝置中 return result;}void I2C_devExit(void){ dev_t devno = MKDEV(gI2C_dev.major, 0); cdev_del(&gI2C_dev.cdev);//從字元裝置中刪除該裝置 unregister_chrdev_region(devno, 1);//回收空間}
- gI2c_devFileOps全域性變數,驅動初始化會用到該結構體變數
- struct file_operations gI2C_devFileOps = {
- .owner = THIS_MODULE,
- .open = I2C_devOpen,
- .release = I2C_devRelease,
- .ioctl = I2C_devIoctl,
- };
int I2C_devInit(void)
{
int result, i;
dev_t dev = 0;
result = alloc_chrdev_region(&dev, 0, 1, I2C_DRV_NAME);//分配字元裝置空間
for(i=0; i<I2C_DEV_MAX_ADDR; i++)
{
gI2C_dev.pObj[i]=NULL;
}
gI2C_dev.major = MAJOR(dev);//儲存裝置主編號
sema_init(&gI2C_dev.semLock, 1);//訊號量初始化
cdev_init(&gI2C_dev.cdev, &gI2C_devFileOps);//使用gI2C_devFileOps初始化該字元裝置,gI2C_devFileOps見下文
gI2C_dev.cdev.owner = THIS_MODULE;//常規賦值
gI2C_dev.cdev.ops = &gI2C_devFileOps;//常規賦值 result = cdev_add(&gI2C_dev.cdev, dev, 1);//新增裝置到字元裝置中 return result;}void I2C_devExit(void){ dev_t devno = MKDEV(gI2C_dev.major, 0); cdev_del(&gI2C_dev.cdev);//從字元裝置中刪除該裝置 unregister_chrdev_region(devno, 1);//回收空間}
gI2c_devFileOps全域性變數,驅動初始化會用到該結構體變數
struct file_operations gI2C_devFileOps = {
.owner = THIS_MODULE,
.open = I2C_devOpen,
.release = I2C_devRelease,
.ioctl = I2C_devIoctl,
};
該驅動只實現了三個函式,open,release和ioctl,對於i2c裝置來說,這已經足夠了。在I2C_devOpen和I2C_devOpen中並沒有做實際的工作,重要的工作均在I2C_devIoctl這個ioctl中完成。I2C_devIoctl程式碼展示(將影響結構條理的程式碼去掉,稍後在做詳細分析) [cpp] view plaincopyprint?
- int I2C_devIoctl(struct inode *inode, struct file *filp, unsigned int cmd, unsigned long arg)
- {
- I2C_Obj *pObj;
- int status=0;
- I2C_TransferPrm transferPrm;
- pObj = (I2C_Obj *)filp->private_data;
- if(!I2C_IOCTL_CMD_IS_VALID(cmd))
- return -1;
- cmd = I2C_IOCTL_CMD_GET(cmd);//cmd命令轉換,防止混淆,具體原因參見上一篇文章:ioctl中的cmd
- down_interruptible(&gI2C_dev.semLock); //訊號量down
- switch(cmd)
- {
- case I2C_CMD_SET_DEV_ADDR://命令1,設定裝置地址
- filp->private_data = I2C_create(arg);
- case I2C_CMD_WRITE: //命令2,寫暫存器值
- status = copy_from_user(&transferPrm, (void *)arg, sizeof(transferPrm));
- ...
- break;
- case I2C_CMD_READ: //命令3,讀暫存器值
- status = copy_from_user(&transferPrm, (void *)arg, sizeof(transferPrm));
- ...
- break;
- default:
- status = -1;
- break;
- }
- up(&gI2C_dev.semLock); //訊號量up
- return status;
- }
int I2C_devIoctl(struct inode *inode, struct file *filp, unsigned int cmd, unsigned long arg)
{
I2C_Obj *pObj;
int status=0;
I2C_TransferPrm transferPrm;
pObj = (I2C_Obj *)filp->private_data;
if(!I2C_IOCTL_CMD_IS_VALID(cmd))
return -1;
cmd = I2C_IOCTL_CMD_GET(cmd);//cmd命令轉換,防止混淆,具體原因參見上一篇文章:ioctl中的cmd
down_interruptible(&gI2C_dev.semLock); //訊號量down
switch(cmd)
{
case I2C_CMD_SET_DEV_ADDR://命令1,設定裝置地址
filp->private_data = I2C_create(arg);
case I2C_CMD_WRITE: //命令2,寫暫存器值
status = copy_from_user(&transferPrm, (void *)arg, sizeof(transferPrm));
...
break;
case I2C_CMD_READ: //命令3,讀暫存器值
status = copy_from_user(&transferPrm, (void *)arg, sizeof(transferPrm));
...
break;
default:
status = -1;
break;
}
up(&gI2C_dev.semLock); //訊號量up
return status;
}
以上三個命令中最重要最複雜的是第一個I2C_CMD_SET_DEV_ADDR,設定裝置地址,之所以重要和複雜,因為在I2C_create()函式中,將通過i2c-core提供的函式把該驅動程式和底層的i2c_adapter聯絡起來。下面是I2C_create()函式原始碼
[cpp]
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- void *I2C_create(int devAddr) {
- int ret;
- struct i2c_driver *driver;
- struct i2c_client *client = client;
- I2C_Obj *pObj;
- devAddr >>= 1;
- if(devAddr>I2C_DEV_MAX_ADDR) //變數合法性判斷
- return NULL;
- if(gI2C_dev.pObj[devAddr]!=NULL) { //變數合法性判斷,如果該地址的裝置已經建立,則調過,防止上層錯誤呼叫
- // already allocated, increment user count, and return the allocated handle
- gI2C_dev.pObj[devAddr]->users++;
- return gI2C_dev.pObj[devAddr];
- }
- pObj = (void*)kmalloc( sizeof(I2C_Obj), GFP_KERNEL); //為pObj分配空間
- gI2C_dev.pObj[devAddr] = pObj; //將分配的空間地址儲存在全域性變數裡
- memset(pObj, 0, sizeof(I2C_Obj));
- pObj->client.adapter = NULL;
- pObj->users++; //使用者基數,初始化為0,當前設為1
- pObj->devAddr = devAddr; //儲存裝置地址
- gI2C_curAddr = pObj->devAddr; //gI2C_curAddr為全域性的整型變數,用於儲存當前的裝置地址
- driver = &pObj->driver; //將成員變數driver單獨抽取出來,因為線面要使用driver來初始化驅動
- pObj->nameSize=0;//i2c裝置名稱,注意,這裡不是在/dev下面的裝置節點名
- pObj->name[pObj->nameSize++] = 'I';
- pObj->name[pObj->nameSize++] = '2';
- pObj->name[pObj->nameSize++] = 'C';
- pObj->name[pObj->nameSize++] = '_';
- pObj->name[pObj->nameSize++] = 'A' + ((pObj->devAddr >> 0) & 0xF);
- pObj->name[pObj->nameSize++] = 'B' + ((pObj->devAddr >> 4) & 0xF);
- pObj->name[pObj->nameSize++] = 0;
- driver->driver.name = pObj->name; //儲存剛才設定的name
- driver->id = I2C_DRIVERID_MISC;
- driver->attach_adapter = I2C_attachAdapter; //這個很重要,將驅動連線到i2c介面卡上,在後面分析
- driver->detach_client = I2C_detachClient; //這個很重,在後面分析
- if((ret = i2c_add_driver(driver))) //使用i2c-core(i2c_register_driver函式)的介面,註冊該驅動,i2c_add_driver實質呼叫了driver_register()
- {
- printk( KERN_ERR "I2C: ERROR: Driver registration failed (address=%x), module not inserted.\n", pObj->devAddr);
- }
- if(ret<0) {
- gI2C_dev.pObj[pObj->devAddr] = NULL;
- kfree(pObj);
- return NULL;
- }
- return pObj;
- }
void *I2C_create(int devAddr) {
int ret;
struct i2c_driver *driver;
struct i2c_client *client = client;
I2C_Obj *pObj;
devAddr >>= 1;
if(devAddr>I2C_DEV_MAX_ADDR) //變數合法性判斷
return NULL;
if(gI2C_dev.pObj[devAddr]!=NULL) { //變數合法性判斷,如果該地址的裝置已經建立,則調過,防止上層錯誤呼叫
// already allocated, increment user count, and return the allocated handle
gI2C_dev.pObj[devAddr]->users++;
return gI2C_dev.pObj[devAddr];
}
pObj = (void*)kmalloc( sizeof(I2C_Obj), GFP_KERNEL); //為pObj分配空間
gI2C_dev.pObj[devAddr] = pObj; //將分配的空間地址儲存在全域性變數裡
memset(pObj, 0, sizeof(I2C_Obj));
pObj->client.adapter = NULL;
pObj->users++; //使用者基數,初始化為0,當前設為1
pObj->devAddr = devAddr; //儲存裝置地址
gI2C_curAddr = pObj->devAddr; //gI2C_curAddr為全域性的整型變數,用於儲存當前的裝置地址
driver = &pObj->driver; //將成員變數driver單獨抽取出來,因為線面要使用driver來初始化驅動
pObj->nameSize=0;//i2c裝置名稱,注意,這裡不是在/dev下面的裝置節點名
pObj->name[pObj->nameSize++] = 'I';
pObj->name[pObj->nameSize++] = '2';
pObj->name[pObj->nameSize++] = 'C';
pObj->name[pObj->nameSize++] = '_';
pObj->name[pObj->nameSize++] = 'A' + ((pObj->devAddr >> 0) & 0xF);
pObj->name[pObj->nameSize++] = 'B' + ((pObj->devAddr >> 4) & 0xF);
pObj->name[pObj->nameSize++] = 0;
driver->driver.name = pObj->name; //儲存剛才設定的name
driver->id = I2C_DRIVERID_MISC;
driver->attach_adapter = I2C_attachAdapter; //這個很重要,將驅動連線到i2c介面卡上,在後面分析
driver->detach_client = I2C_detachClient; //這個很重,在後面分析
if((ret = i2c_add_driver(driver))) //使用i2c-core(i2c_register_driver函式)的介面,註冊該驅動,i2c_add_driver實質呼叫了driver_register()
{
printk( KERN_ERR "I2C: ERROR: Driver registration failed (address=%x), module not inserted.\n", pObj->devAddr);
}
if(ret<0) {
gI2C_dev.pObj[pObj->devAddr] = NULL;
kfree(pObj);
return NULL;
}
return pObj;
}
其他兩個命令是I2C_CMD_WRITE和I2C_CMD_READ,這個比較簡單,只需