解析linux或android添加文件系统的属性接口的方法

第一种：

1、添加关键头文件：

#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、在已经存在驱动文件中搜索"DEVICE_ATTR"关键字，如果存在，直接参考已经存在的方法添加一个即可，如下：

unsigned int Gpio134_OtgID = 134; //定义全局变量
static unsigned int otgid_status = 1;
…

3、定义文件系统的读写函数：

//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);
 
//setotgid的一致性，第一个参数setotgid和setotgid_show、setotgid_store前钻必须保持一致
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定义的name必须保持一致
 NULL
};

4、在probe()函数中定义针对具体GPIO管脚的请求和初始化

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){ //有自定义初始化状态就添加上这个判断，没有就不需要添加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()函数中添加资源的释放

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
 ........................................................
}

第二种方法：

在要添加驱动文件中没有搜索"DEVICE_ATTR"关键字的情况，如添加音频功放打开和关闭的控制接口：
1、添加关键头文件：

#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、定义全局变量和定义打开和关闭的接口并组织属性数组：

// 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__);
 //功放打开的时序
 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__);
 //功放关闭的时序
 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()函数中添加文件系统属性接口的注册：
在注册的时候并不需要对功放进行初始化，所以probe()函数中并没有对sdm660_cdc->spk_pa_gpio(GPIO63)，只操作了请求。具体的请求操作请参考：msm8953 audio部分的EAR和Speaker输出的声音配置中的音频部分的

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; //将设备树种定义的IO口号获取进来
 spk_pa_kobj = kobject_create_and_add("spk_pa", NULL); //创建/sys/spk_pa/目录
 ret = sysfs_create_group(spk_pa_kobj, &apkpa_attr_group); //创建/sys/class/spk_pa/spkpaon节点
 if (ret)
 dev_err(&pdev->dev,"%s:sysfs_create_group failed with error\n",__func__);
 //end zhaojr add 
 ....................................

4、在remove函数中释放资源

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 //释放资源
 gpio_free(sdm660_cdc->spk_pa_gpio);
 kobject_put(spk_pa_kobj); //关键函数
 sysfs_remove_group(spk_pa_kobj, &apkpa_attr_group); //关键函数
 //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;
}

总结

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