久久婷婷香蕉热狠狠综合,精品无码国产自产拍在线观看蜜,寡妇房东在做爰3,中文字幕日本人妻久久久免费,国产成人精品三上悠亚久久

實例解析linux內核I2C體系結構（2）

四、在(zai)內核里寫(xie)i2c設備驅動的兩種方式

在《實例解析linux內核I2C體系結構（1）》一(yi)文介紹(shao)(shao)了(le)利用(yong)/dev/i2c-0在應用(yong)層(ceng)完(wan)成(cheng)對i2c設備的(de)操作，但(dan)很多時候我們還是習(xi)慣(guan)為i2c設備在內核層(ceng)編寫驅動(dong)程序。目(mu)前(qian)內核支持兩種編寫i2c驅動(dong)程序的(de)方(fang)(fang)式(shi)(shi)(shi)(shi)。下面分(fen)別介紹(shao)(shao)這(zhe)兩種方(fang)(fang)式(shi)(shi)(shi)(shi)的(de)實現。這(zhe)里分(fen)別稱這(zhe)兩種方(fang)(fang)式(shi)(shi)(shi)(shi)為“Adapter方(fang)(fang)式(shi)(shi)(shi)(shi)（LEGACY）”和“Probe方(fang)(fang)式(shi)(shi)(shi)(shi)（new style）”。

（1） Adapter方式（LEGACY）

（下面的(de)實例代碼是在2.6.27內(nei)核的(de)pca953x.c基礎上(shang)修改的(de)，原始代碼采用(yong)的(de)是本(ben)文將(jiang)要討論的(de)第(di)2種方式，即Probe方式）

●    構建(jian)i2c_driver

static struct i2c_driver pca953x_driver = {
                .driver = {
                                    .name= "pca953x", //名稱
                                },
                .id= ID_PCA9555,//id號
                .attach_adapter= pca953x_attach_adapter, //調用適配器連接設備
                .detach_client= pca953x_detach_client,//讓設備脫離適配器
        };

●    注(zhu)冊i2c_driver

static int __init pca953x_init(void)
        {
                return i2c_add_driver(&pca953x_driver);
        }
         module_init(pca953x_init);

●    attach_adapter動作

執行i2c_add_driver(&pca953x_driver)后會(hui)，如(ru)果(guo)內核中已經注冊了i2c適配器(qi)，則(ze)順序調用(yong)這些(xie)適配器(qi)來(lai)連接我們的(de)i2c設備。此(ci)過程是(shi)通(tong)過調用(yong)i2c_driver中的(de)attach_adapter方法完(wan)成的(de)。具(ju)體(ti)實現(xian)形式如(ru)下：

static int pca953x_attach_adapter(struct i2c_adapter *adapter)
        {
                return i2c_probe(adapter, &addr_data, pca953x_detect);
                /*
                adapter:適配器
                addr_data:地址信息
                pca953x_detect：探測到設備后調用的函數
                */
        }

地址信息addr_data是由下面代碼指定的。
        /* Addresses to scan */
        static unsigned short normal_i2c[] = {0x20,0x21,0x22,0x23,0x24,0x25,0x26,0x27,I2C_CLIENT_END};
        I2C_CLIENT_INSMOD;

注(zhu)意：normal_i2c里的地(di)址(zhi)(zhi)必須是(shi)你i2c芯片(pian)的地(di)址(zhi)(zhi)。否(fou)則將無法(fa)正確探測到(dao)設(she)備。而I2C_ CLIENT_INSMOD是(shi)一個宏，它會(hui)利用(yong)normal_i2c構建(jian)addr_data。

●    構建i2c_client，并注冊(ce)字符(fu)設(she)備驅動

i2c_probe在(zai)探測到目標設備后，后調用pca953x_detect，并把當(dang)時的探測地(di)址address作為參數傳入(ru)。

static int pca953x_detect(struct i2c_adapter *adapter, int address, int kind)
        {
                struct i2c_client *new_client;
                struct pca953x_chip *chip; //設備結構體
                int err = 0,result;
                dev_t pca953x_dev=MKDEV(pca953x_major,0);//構建設備號，根據具體情況設定，這里我只考慮了normal_i2c中只有一個地址匹配的情況。
                if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE_DATA| I2C_FUNC_SMBUS_WORD_DATA))//判定適配器能力
                goto exit;
                if (!(chip = kzalloc(sizeof(struct pca953x_chip), GFP_KERNEL))) {
                        err = -ENOMEM;
                        goto exit;
                }
                /****構建i2c-client****/
                chip->client=kzalloc(sizeof(struct i2c_client),GFP_KERNEL);
                new_client = chip->client;
                i2c_set_clientdata(new_client, chip);
                new_client->addr = address;
                new_client->adapter = adapter;
                new_client->driver = &pca953x_driver;
                new_client->flags = 0;
                strlcpy(new_client->name, "pca953x", I2C_NAME_SIZE);
                if ((err = i2c_attach_client(new_client)))//注冊i2c_client
                goto exit_kfree;
                if (err)
                goto exit_detach;
                if(pca953x_major)
                {
                        result=register_chrdev_region(pca953x_dev,1,"pca953x");
                }
                else{
                        result=alloc_chrdev_region(&pca953x_dev,0,1,"pca953x");
                        pca953x_major=MAJOR(pca953x_dev);
                }
                if (result < 0) {
                        printk(KERN_NOTICE "Unable to get pca953x region, error %d\n", result);
                        return result;
                }
                pca953x_setup_cdev(chip,0); //注冊字符設備，此處不詳解
                return 0;
                exit_detach:
                i2c_detach_client(new_client);
        exit_kfree:
                kfree(chip);
        exit:
                return err;
&nbsp;       }

i2c_check_functionality用來(lai)判定設配(pei)器(qi)的能力，這一點非常重要。你也可以直接查看(kan)對應設配(pei)器(qi)的能力，如

static const struct i2c_algorithm smbus_algorithm = {
                .smbus_xfer= i801_access,
                .functionality= i801_func,
        };
        static u32 i801_func(struct i2c_adapter *adapter)
        {
                        return I2C_FUNC_SMBUS_QUICK | I2C_FUNC_SMBUS_BYTE |
                    I2C_FUNC_SMBUS_BYTE_DATA | I2C_FUNC_SMBUS_WORD_DATA |
                I2C_FUNC_SMBUS_BLOCK_DATA | I2C_FUNC_SMBUS_WRITE_I2C_BLOCK
                                | (isich4 ? I2C_FUNC_SMBUS_HWPEC_CALC : 0);
    &nbsp;&nbsp;  }

●    字符(fu)驅動的(de)具(ju)體實現

struct file_operations pca953x_fops = {
                .owner = THIS_MODULE,
                .ioctl= pca953x_ioctl, 
                .open= pca953x_open, 
                .release =pca953x_release, 
     &nbsp;   };

字符設(she)備驅(qu)動本身沒(mei)有(you)什么好說的，這里主(zhu)要想說一下(xia)，如何(he)在驅(qu)動中(zhong)調(diao)用i2c設(she)配器(qi)幫我們完成數據(ju)傳(chuan)輸。

目前設配器(qi)(qi)主要支(zhi)(zhi)持(chi)兩種傳(chuan)輸(shu)方法：smbus_xfer和master_xfer。一(yi)般來說(shuo)，如果設配器(qi)(qi)支(zhi)(zhi)持(chi)了master_xfer那(nei)么它也可以模擬支(zhi)(zhi)持(chi)smbus的傳(chuan)輸(shu)。但如果只實現smbus_xfer，則不支(zhi)(zhi)持(chi)一(yi)些i2c的傳(chuan)輸(shu)。

int (*master_xfer)(struct i2c_adapter *adap,struct i2c_msg *msgs,int num);
        int (*smbus_xfer) (struct i2c_adapter *adap, u16 addr,
                                                                                unsigned short flags, char read_write,
                      &nbsp;                                         u8 command, int size, union i2c_smbus_data * data);

master_xfer中的參數設(she)置(zhi)，和(he)前面的用(yong)戶(hu)空間(jian)編程一致(zhi)。現在(zai)只是要在(zai)驅動(dong)中構建相(xiang)關的參數然后調用(yong)i2c_transfer來(lai)完成傳輸既可。

int i2c_transfer(struct i2c_adapter * adap, struct i2c_msg *msgs, int num)

smbus_xfer中的參數(shu)設置(zhi)及調用方法(fa)如下：

static int pca953x_write_reg(struct pca953x_chip *chip, int reg, uint16_t val)
        {
                int ret;
                ret = i2c_smbus_write_word_data(chip->client, reg << 1, val);
                if (ret < 0) {
                                dev_err(&chip->client->dev, "failed writing register\n");
                                        return -EIO;
                                }
                return 0;
   &nbsp;    }

上(shang)面函數完(wan)成向芯(xin)片的地址為reg的寄(ji)存器寫一個16bit的數據。i2c_smbus_write_word_data的實現如下：

s32 i2c_smbus_write_word_data(struct i2c_client *client, u8 command, u16 value)
        {
                union i2c_smbus_data data;
                data.word = value;
                return i2c_smbus_xfer(client->adapter,client->addr,client->flags,
                                                                        I2C_SMBUS_WRITE,command,
                                                                        I2C_SMBUS_WORD_DATA,&data);
  ;      }

從中(zhong)(zhong)可以(yi)看出smbus傳輸一個16位數據(ju)的(de)(de)方法(fa)。其它(ta)操(cao)作如：字(zi)符寫、字(zi)符讀(du)、字(zi)讀(du)、塊操(cao)作等，可以(yi)參(can)考內核的(de)(de)i2c-core.c中(zhong)(zhong)提供的(de)(de)方法(fa)。

●    注銷i2c_driver

static void __exit pca953x_exit(void)
        {
                i2c_del_driver(&pca953x_driver);
        }
        module_exit(pca953x_exit);

●    detach_client動作

順序調用內核中注冊的(de)適配器來斷開(kai)我們注冊過的(de)i2c設備。此過程通過調用i2c_driver中的(de)attach_adapter方法完(wan)成的(de)。具體實現形(xing)式如下：

static int pca953x_detach_client(struct i2c_client *client)
        {
                int err;
                struct pca953x_chip *data;
                if ((err = i2c_detach_client(client)))//斷開i2c_client
                return err;
                data=i2c_get_clientdata(client);
                cdev_del(&(data->cdev));
                unregister_chrdev_region(MKDEV(pca953x_major, 0), 1);
                kfree(data->client);
                kfree(data);
                return 0;
&nbsp;  &nbsp;    }

（2） Probe方式(shi)（new style）

●    構建i2c_driver

和LEGACY方式一樣，也需(xu)要構建i2c_driver，但是(shi)內容有所不同。

static struct i2c_driver pca953x_driver = {
                .driver = {
                        .name= "pca953x",
                        },
                        .probe= pca953x_probe, //當有i2c_client和i2c_driver匹配時調用
                        .remove= pca953x_remove,//注銷時調用
                        .id_table= pca953x_id,//匹配規則
      &nbsp; };

●    注冊i2c_driver

static int __init pca953x_init(void)
        {
                return i2c_add_driver(&pca953x_driver);
        }
        module_init(pca953x_init);

在注(zhu)冊i2c_driver的(de)(de)過程中，是(shi)將driver注(zhu)冊到了i2c_bus_type的(de)(de)總(zong)線上(shang)。此總(zong)線的(de)(de)匹配規則(ze)是(shi)：

static const struct i2c_device_id *i2c_match_id(const struct i2c_device_id *id,
                                                                                                const struct i2c_client *client)
        {
                while (id->name[0]) {
                        if (strcmp(client->name, id->name) == 0)
                                return id;
                        id++;
                }
                return NULL;
  ;      }

可以看(kan)出是利(li)用i2c_client的(de)(de)名(ming)稱和id_table中的(de)(de)名(ming)稱做匹配的(de)(de)。本驅動中的(de)(de)id_table為

static const struct i2c_device_id pca953x_id[] = {
                { "pca9534", 8, },
                { "pca9535", 16, },
                { "pca9536", 4, },
                { "pca9537", 4, },
                { "pca9538", 8, },
                { "pca9539", 16, },
                { "pca9554", 8, },
                { "pca9555", 16, },
                { "pca9557", 8, },
                { "max7310", 8, },
                { }
        ; };

看到現在我們(men)應該會有這樣的(de)疑問，在Adapter模式中，i2c_client是(shi)我們(men)自己構(gou)造出來(lai)的(de)，而現在的(de)i2c_client是(shi)從哪來(lai)的(de)呢(ni)？看看下面(mian)的(de)解釋

●    注冊i2c_board_info

對于Probe模(mo)式(shi)，通常在平臺代碼中要完(wan)成i2c_board_info的注冊。方法如下：

static struct i2c_board_info __initdata test_i2c_devices[] = {
                {
                        I2C_BOARD_INFO("pca9555", 0x27),//pca9555為芯片名稱，0x27為芯片地址
                        .platform_data = &pca9555_data,
                }, {
                        I2C_BOARD_INFO("mt9v022", 0x48),
                        .platform_data = &iclink[0], /* With extender */
                }, {
                        I2C_BOARD_INFO("mt9m001", 0x5d),
                        .platform_data = &iclink[0], /* With extender */
                },
        };
        i2c_register_board_info(0, test_i2c_devices,ARRAY_SIZE(test_i2c_devices)); //注冊

i2c_client就是(shi)在注冊過程(cheng)中構建的。但有一點需要注意的是(shi)i2c_register_board_info并沒有EXPORT_SYMBOL給模(mo)塊使(shi)用(yong)。

●    字符驅動注冊(ce)

在(zai)Probe方式下，添加字符驅動(dong)的位置在(zai)pca953x_probe中。

static int __devinit pca953x_probe(struct i2c_client *client,const struct i2c_device_id *id)
        {
                        ……
                        /****字符設備驅動注冊位置****/
                        ……
                        return 0;
        &nbsp;}

●    注銷(xiao)i2c_driver

static void __exit pca953x_exit(void)
        {
                i2c_del_driver(&pca953x_driver);
        }
        module_exit(pca953x_exit);

●    注銷字符(fu)設備驅動

 在(zai)Probe方式下，注(zhu)銷(xiao)字符驅動的位置在(zai)pca953x_remove中。

static int __devinit pca953x_remove (struct i2c_client *client)
        {
                ……
                /****字符設備驅動注銷的位置****/
                ……
                return 0;
    &nbsp;  &nbsp;}

●&nbsp;   I2C設備(bei)的數據交互方法(即：調用適(shi)配器操作設備(bei)的方法)和Adapter方式下相同。