linux或android添加文件系統的屬性接口的方法

第一種：
1、添加關鍵頭文件：

#include <linux/of_gpio.h>
#include <linux/gpio.h>
#include <linux/delay.h>

#include <linux/module.h>
#include <linux/types.h>
#include <linux/kobject.h>

2、在已經存在驅動文件中搜索"DEVICE_ATTR"關鍵字，如果存在，直接參考已經存在的方法添加一個即可，如下：
unsigned int Gpio134_OtgID = 134; //定義全局變量
static unsigned int otgid_status = 1;
…
3、定義文件系統的讀寫函數：

//add zhaojr  gpio134 control OTG ID for host or device mode 
static ssize_t setotgid_store(struct device *dev, struct device_attribute *attr,const char *buf, size_t count)                         
{
    unsigned int ret=0;
    pr_err("%s: \n", __func__);    
    //ret = kstrtoint(buf, 10, &otgid_status);
    ret = kstrtouint(buf, 10, &otgid_status);
    //sscanf(buf, "%lu", &otgid_status);
    if (ret < 0){
        pr_err("%s::kstrtouint() failed \n", __func__);
    }
    //sscanf(buf, "%d", &otgid_status);
    pr_err("%s: otgid_status=%d \n", __func__,otgid_status);    
    if(otgid_status  > 0){
        gpio_set_value(Gpio134_OtgID, 1); 
    }else{
        gpio_set_value(Gpio134_OtgID, 0); 
    }
    return count;
}
static ssize_t setotgid_show(struct device *dev,struct device_attribute *attr, char *buf)        
{
   pr_err("%s: \n", __func__);    
   return sprintf(buf, "%d\n",otgid_status);
}
//static DEVICE_ATTR_RW(setotgid);
/*struct device_attribute dev_attr_setotgid = {                    
        .attr = {.name ="setotgid",                         
        .mode = 0664},            
        .show    = setotgid_show,                            
        .store    = setotgid_store,                
};*/   
//setotgid的一致性，第一個參數setotgid和setotgid_show、setotgid_store前鑽必須保持一致
static DEVICE_ATTR(setotgid, 0664, setotgid_show, setotgid_store); 
//end zhaojr add
static struct device_attribute *android_usb_attributes[] = {
    &dev_attr_state,
    &dev_attr_setotgid, //setotgid跟DEVICE_ATTR定義的name必須保持一致
    NULL
};

4、在probe()函數中定義針對具體GPIO管腳的請求和初始化

static int mdss_mdp_probe(struct platform_device *pdev)
{
....................................................................................
//zhaojr add for gpio134 to usb host or device mode
    ret_status=gpio_request(Gpio134_OtgID, "Gpio134-OtgID");
    if(ret_status<0){
        pr_err("usb gadget configfs %s::Gpio134_OtgID gpio_request failed\n",__func__);    
        }
    pr_err("android_device_create()::Gpio134_OtgID gpio_request OK\n");    
    gpio_direction_output(Gpio134_OtgID,1);
    if(otgid_status > 0){ //有自定義初始化狀態就添加上這個判斷，沒有就不需要添加if  else操作
        pr_err("%s-Gpio134_OtgID pin set 1\n", __func__);
        gpio_set_value(Gpio134_OtgID, 1); 
        //msleep(5);
    }else{
        pr_err("%s-Gpio134_OtgID pin set 0\n", __func__);
        gpio_set_value(Gpio134_OtgID, 0); 
        //msleep(5);
    }
    //end zhaojr add
................................................................
}

5、在remove()函數中添加資源的釋放

static int mdss_mdp_remove(struct platform_device *pdev)
{
    struct mdss_data_type *mdata = platform_get_drvdata(pdev);
    if (!mdata)
        return -ENODEV; 
    pr_err("%s\n", __func__);
    gpio_free(Gpio134_OtgID);    //zhaojr add free gpio otgid pin
  ........................................................
}

第二種方法：
在要添加驅動文件中沒有搜索"DEVICE_ATTR"關鍵字的情況，如添加音頻功放打開和關閉的控制接口：
1、添加關鍵頭文件：

#include <linux/of_gpio.h>
#include <linux/gpio.h>
#include <linux/delay.h>

#include <linux/module.h>
#include <linux/types.h>
#include <linux/kobject.h>

2、定義全局變量和定義打開和關閉的接口並組織屬性數組：

// add zhaojr  gpio63 for close or speaker pa enable
struct kobject *spk_pa_kobj = NULL;
unsigned int gpio63_spk_pa_gpio;  //for speaker pa ic enable
//extern unsigned int gpio63_spk_pa_gpio;
static unsigned int SpkPa_Gpio_Enable = 0;
static ssize_t spkpaon_store(struct device *dev, struct device_attribute *attr,const char *buf, size_t count)				 		
{
	unsigned int ret=0;
	//ret = kstrtoint(buf, 10, &backlight_enable);
	ret = kstrtouint(buf, 10, &SpkPa_Gpio_Enable);
	if (ret < 0){
		pr_err("%s::kstrtouint() failed \n", __func__);
	}
	pr_err("%s: SpkPa_Gpio_Enable=%d \n", __func__,SpkPa_Gpio_Enable);	
	if(SpkPa_Gpio_Enable  > 0){
		//gpio_set_value(gpio63_spk_pa_gpio, 1); 
		pr_err("%s: gpio_set_value gpio63 speaker pa enable \n", __func__);
		//功放打開的時序
		gpio_set_value(gpio63_spk_pa_gpio,0);
		udelay(8);
		gpio_set_value(gpio63_spk_pa_gpio,1);
		udelay(8);
		gpio_set_value(gpio63_spk_pa_gpio,0);
		udelay(8);
		gpio_set_value(gpio63_spk_pa_gpio,1);
		//sdm660_cdc->ext_spk_pa_set = true;
	}else{
		pr_err("%s: gpio_set_value gpio63 speaker pa disable \n", __func__);
		//功放關閉的時序
		gpio_set_value(gpio63_spk_pa_gpio,0);
		udelay(600);
		//sdm660_cdc->ext_spk_pa_set = false; 
	}
	return count;
}
static ssize_t spkpaon_show(struct device *dev,struct device_attribute *attr, char *buf)		
{	
   return sprintf(buf, "%d\n",SpkPa_Gpio_Enable);
}   
static DEVICE_ATTR(spkpaon, 0664, spkpaon_show, spkpaon_store);
static struct attribute *spkpa_attributes[] = {
	&dev_attr_spkpaon.attr,
	NULL
};
static const struct attribute_group apkpa_attr_group = {
	.attrs = spkpa_attributes,
	NULL
};
//end zhaojr add

3、在probe()函數中添加文件系統屬性接口的註冊：
在註冊的時候並不需要對功放進行初始化，所以probe()函數中並沒有對sdm660_cdc->spk_pa_gpio(GPIO63)，只操作了請求。具體的請求操作請參考：msm8953 audio部分的EAR和Speaker輸出的聲音配置中的音頻部分的
vendor/qcom/opensource/audio-kernel/asoc/codecs/sdm660_cdc/msm-analog-cdc.c文件操作

static int msm_anlg_cdc_probe(struct platform_device *pdev)
{
	int ret = 0;
	struct sdm660_cdc_priv *sdm660_cdc = NULL;
	struct sdm660_cdc_pdata *pdata;
	int adsp_state;
	..................................
	dev_set_drvdata(&pdev->dev, sdm660_cdc);
	//kangting add
	sdm660_cdc->spk_pa_gpio = of_get_named_gpio(pdev->dev.of_node, "qcom,speaker-pa", 0);
	if (!gpio_is_valid(sdm660_cdc->spk_pa_gpio))
		pr_err("%s, sdm660_cdc->spk_pa_gpio not specified\n",__func__);
	else{
		pr_err("%s, sdm660_cdc->spk_pa_gpio is %d\n",__func__,sdm660_cdc->spk_pa_gpio);
		ret = gpio_request(sdm660_cdc->spk_pa_gpio, "spk_pa");
		if (ret) {
			pr_err("request spk_pa_gpio failed, ret=%d\n",ret);
			gpio_free(sdm660_cdc->spk_pa_gpio);
		}
	}
	//kangting end
	ret = snd_soc_register_codec(&pdev->dev,
				     &soc_codec_dev_sdm660_cdc,
				     msm_anlg_cdc_i2s_dai,
				     ARRAY_SIZE(msm_anlg_cdc_i2s_dai));
	if (ret) {
		dev_err(&pdev->dev,
			"%s:snd_soc_register_codec failed with error %d\n",
			__func__, ret);
		goto err_supplies;
	}
	BLOCKING_INIT_NOTIFIER_HEAD(&sdm660_cdc->notifier);
	BLOCKING_INIT_NOTIFIER_HEAD(&sdm660_cdc->notifier_mbhc);
	//add by zhaojr
    gpio63_spk_pa_gpio = sdm660_cdc->spk_pa_gpio; //將設備樹種定義的IO口號獲取進來
	spk_pa_kobj = kobject_create_and_add("spk_pa", NULL); //創建/sys/spk_pa/目錄
	ret = sysfs_create_group(spk_pa_kobj, &apkpa_attr_group); //創建/sys/class/spk_pa/spkpaon節點
	if (ret)
		dev_err(&pdev->dev,"%s:sysfs_create_group failed with error\n",__func__);
	//end zhaojr add	
	....................................

4、在remove函數中釋放資源

static int msm_anlg_cdc_remove(struct platform_device *pdev)
{
	struct sdm660_cdc_priv *sdm660_cdc = dev_get_drvdata(&pdev->dev);
	struct sdm660_cdc_pdata *pdata = sdm660_cdc->dev->platform_data;
	int count;
	//add by zhaojr //釋放資源
	gpio_free(sdm660_cdc->spk_pa_gpio);
	kobject_put(spk_pa_kobj); //關鍵函數
 	sysfs_remove_group(spk_pa_kobj, &apkpa_attr_group); //關鍵函數
	//end zhaojr add
	for (count = 0; count < sdm660_cdc->child_count &&
				count < ANLG_CDC_CHILD_DEVICES_MAX; count++)
		platform_device_unregister(
				sdm660_cdc->pdev_child_devices[count]);
	snd_soc_unregister_codec(&pdev->dev);
	msm_anlg_cdc_disable_supplies(sdm660_cdc, pdata);
	wcd9xxx_spmi_irq_exit();
	devm_kfree(&pdev->dev, sdm660_cdc);
	return 0;
}