Android中LCD背光驱动
16lz
2021-01-23
分类: Linux驱动 Android系统 2013-06-17 16:28 287人阅读评论(0)收藏 举报
亮度设置的java源文件在:mydroid/packages/apps/Settings/src/com/android/settings/BrightnessPreference.java
打开这个文件看到:[java] view plain copy print ?
这一层就是调用HAL层的方法,为上一层实现一个设置亮度接口。
先浏览欣赏一下light.c先[cpp] view plain copy print ?
这一层的采用Linux的platform device/driver 模型。它最终会调用Linux内核层leds-class.c的接口。看看它的probe函数片段:[cpp] view plain copy print ?
需关注这里设置了info->pri_display_class_dev.name = "lcd-backlight";,然后调用led_classdev_register函数注册,所以完美解释了led_cdev->name就是"lcd-backlight",完美解释了"/sys/class/leds/lcd-backlight/brightness"的由来。
另外info->pri_display_class_dev.brightness_set = omap4_xxx_primary_disp_store;中的omap4_xxx_primary_disp_store()就是我们需要实现的设置背光亮度函数,函数里面就是pwm操作。到这里又有一个疑问4:为什么只实现设置背光亮度的接口,而没有实现读取当前亮度量化值的接口?其实Android上层自行处理了这个获取亮度量化值的事情,也就是说Android上层设置了亮度是多少,上层会执行保留设置结果。无需再通过下层读取。
目录(?)[+]
- Android的Setting
- Android的背光JNI层
- Android的背光HAL层
- Linux的背光内核层
- Linux的背光驱动层
- 总结
其实Android的底层就是Linux,所以其驱动本质就是Linux驱动,但是这些Linux驱动是服务上层Android的,所以需遵循上Android的一些接口规范。所以涉及到的Android驱动都应应密切关注上层传递的接口。本文介绍的LCD背光驱动就是从上层一直往下层展现,但是笔者毕竟不是专注于Android上层,碍于知识不充裕,所以对上层的东西介绍得相对简单。
1.Android的Setting
Android的设置里面管理了Andoird系统的所有设置,其中当然包括了屏幕亮度设置。Setting的源码目录在:mydroid/packages/apps/Settings/src/com/android/settings亮度设置的java源文件在:mydroid/packages/apps/Settings/src/com/android/settings/BrightnessPreference.java
打开这个文件看到:[java] view plain copy print ?
- publicclassBrightnessPreferenceextendsSeekBarDialogPreferenceimplements
- SeekBar.OnSeekBarChangeListener,CheckBox.OnCheckedChangeListener{
- privateSeekBarmSeekBar;
- privateCheckBoxmCheckBox;
- privateintmOldBrightness;
- privateintmOldAutomatic;
- privatebooleanmAutomaticAvailable;
- privatebooleanmRestoredOldState;
- //Backlightrangeisfrom0-255.Needtomakesurethatuser
- //doesn'tsetthebacklightto0andgetstuck
- privateintmScreenBrightnessDim=
- ...
public class BrightnessPreference extends SeekBarDialogPreference implements SeekBar.OnSeekBarChangeListener, CheckBox.OnCheckedChangeListener { private SeekBar mSeekBar; private CheckBox mCheckBox; private int mOldBrightness; private int mOldAutomatic; private boolean mAutomaticAvailable; private boolean mRestoredOldState; // Backlight range is from 0 - 255. Need to make sure that user // doesn't set the backlight to 0 and get stuck private int mScreenBrightnessDim =...Android的最上层已经将背光亮度量化为了[0,255]个等级,并且提示注意不要设置为0,所以在进行最低层的背光驱动编写时,可以合理按这个范围部署背光的亮度。
2.Android的背光JNI层
背光的JNI层源码在:mydroid/frameworks/base/services/jni/com_android_server_LightsService.cpp这一层就是调用HAL层的方法,为上一层实现一个设置亮度接口。
3.Android的背光HAL层
Java App和JNI一般是google维护的,所以源码位置相对固定,HAL有产品商开发维护的,所以位置是不固定的,看产品上喜好,笔者使用的TI OMAP4平台,背光的HAL层代码就在:mydroid/device/ti/xxx_product/liblights/light.c先浏览欣赏一下light.c先[cpp] view plain copy print ?
- /*
- *Copyright(C)2008TheAndroidOpenSourceProject
- *
- *LicensedundertheApacheLicense,Version2.0(the"License");
- *youmaynotusethisfileexceptincompliancewiththeLicense.
- *YoumayobtainacopyoftheLicenseat
- *
- *http://www.apache.org/licenses/LICENSE-2.0
- *
- *Unlessrequiredbyapplicablelaworagreedtoinwriting,software
- *distributedundertheLicenseisdistributedonan"ASIS"BASIS,
- *WITHOUTWARRANTIESORCONDITIONSOFANYKIND,eitherexpressorimplied.
- *SeetheLicenseforthespecificlanguagegoverningpermissionsand
- *limitationsundertheLicense.
- */
- #defineLOG_TAG"lights"
- #include<cutils/log.h>
- #include<stdint.h>
- #include<string.h>
- #include<unistd.h>
- #include<errno.h>
- #include<fcntl.h>
- #include<pthread.h>
- #include<sys/ioctl.h>
- #include<sys/types.h>
- #include<hardware/lights.h>
- /******************************************************************************/
- staticpthread_once_tg_init=PTHREAD_ONCE_INIT;
- staticpthread_mutex_tg_lock=PTHREAD_MUTEX_INITIALIZER;
- charconst*constLCD_FILE
- ="/sys/class/leds/lcd-backlight/brightness";
- charconst*constKEYBOARD_FILE
- ="/sys/class/leds/keyboard-backlight/brightness";
- charconst*constCHARGING_LED_FILE
- ="/sys/class/leds/battery-led/brightness";
- /*RGBfiledescriptors*/
- charconst*constRED_LED_FILE
- ="/sys/class/leds/red/brightness";
- charconst*constRED_DELAY_ON_FILE
- ="/sys/class/leds/red/delay_on";
- charconst*constRED_DELAY_OFF_FILE
- ="/sys/class/leds/red/delay_off";
- charconst*constGREEN_LED_FILE
- ="/sys/class/leds/green/brightness";
- charconst*constGREEN_DELAY_ON_FILE
- ="/sys/class/leds/green/delay_on";
- charconst*constGREEN_DELAY_OFF_FILE
- ="/sys/class/leds/green/delay_off";
- charconst*constBLUE_LED_FILE
- ="/sys/class/leds/blue/brightness";
- charconst*constBLUE_DELAY_ON_FILE
- ="/sys/class/leds/blue/delay_on";
- charconst*constBLUE_DELAY_OFF_FILE
- ="/sys/class/leds/blue/delay_off";
- ...
/* * Copyright (C) 2008 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */#define LOG_TAG "lights"#include <cutils/log.h>#include <stdint.h>#include <string.h>#include <unistd.h>#include <errno.h>#include <fcntl.h>#include <pthread.h>#include <sys/ioctl.h>#include <sys/types.h>#include <hardware/lights.h>/******************************************************************************/static pthread_once_t g_init = PTHREAD_ONCE_INIT;static pthread_mutex_t g_lock = PTHREAD_MUTEX_INITIALIZER;char const*const LCD_FILE = "/sys/class/leds/lcd-backlight/brightness";char const*const KEYBOARD_FILE = "/sys/class/leds/keyboard-backlight/brightness";char const*const CHARGING_LED_FILE = "/sys/class/leds/battery-led/brightness";/*RGB file descriptors */char const*const RED_LED_FILE = "/sys/class/leds/red/brightness";char const*const RED_DELAY_ON_FILE = "/sys/class/leds/red/delay_on";char const*const RED_DELAY_OFF_FILE = "/sys/class/leds/red/delay_off";char const*const GREEN_LED_FILE = "/sys/class/leds/green/brightness";char const*const GREEN_DELAY_ON_FILE = "/sys/class/leds/green/delay_on";char const*const GREEN_DELAY_OFF_FILE = "/sys/class/leds/green/delay_off";char const*const BLUE_LED_FILE = "/sys/class/leds/blue/brightness";char const*const BLUE_DELAY_ON_FILE = "/sys/class/leds/blue/delay_on";char const*const BLUE_DELAY_OFF_FILE = "/sys/class/leds/blue/delay_off";...[cpp] view plain copy print ?
- staticint
- set_light_backlight(structlight_device_t*dev,
- structlight_state_tconst*state)
- {
- interr=0;
- intbrightness=rgb_to_brightness(state);
- pthread_mutex_lock(&g_lock);
- err=write_int(LCD_FILE,brightness);
- pthread_mutex_unlock(&g_lock);
- returnerr;
- }
static intset_light_backlight(struct light_device_t* dev, struct light_state_t const* state){ int err = 0; int brightness = rgb_to_brightness(state); pthread_mutex_lock(&g_lock); err = write_int(LCD_FILE, brightness); pthread_mutex_unlock(&g_lock); return err;}这里关注一下LCD背光的sys文件节点:"/sys/class/leds/lcd-backlight/brightness"疑问1:这个sys接口是谁约定的呢?疑问2:可不可以改这个接口呢?疑问3:为什么这里还有其他led的很多sys文件节点呢:先解释疑问3,因为一个Android设备,不只是有LCD背光的LED,还有可以有其他很多LED(当然也可以没有),所以这里一并实现了这些LED的HAL,产品商可以沿用这些HAL。先来试验一把:启动Android设备,在Setting里更改亮度,然后在串口命令行中或“adb shell"中运行命令cat /sys/class/leds/lcd-backlight/brightness,会发现Setting的更改后可以通过cat 显示Setting的更改。所以更加确认了这个"/sys/class/leds/lcd-backlight/brightness"接口是正确的。因为HAL层是和Linux Kernel交互的,所以这里如果能cat实现读取亮度等级,那么在Linux kernel层就一定实现了sysfs接口。
4.Linux的背光内核层
背光的内核层源码在:driver/leds/led-class.c这一层由内核开发者去维护,不用我们操心。看看它的init函数[cpp] view plain copy print ?- staticint__initleds_init(void)
- {
- leds_class=class_create(THIS_MODULE,"leds");
- if(IS_ERR(leds_class))
- returnPTR_ERR(leds_class);
- leds_class->suspend=led_suspend;
- leds_class->resume=led_resume;
- leds_class->dev_attrs=led_class_attrs;
- return0;
- }
static int __init leds_init(void){leds_class = class_create(THIS_MODULE, "leds");if (IS_ERR(leds_class))return PTR_ERR(leds_class);leds_class->suspend = led_suspend;leds_class->resume = led_resume;leds_class->dev_attrs = led_class_attrs;return 0;}好明显,正是由于它创建了sys class,名字为”leds“,所以上面的背光sys文件节点"/sys/class/leds/”就有了来由,那么剩下的“../lcd-backlight/brightness"又是怎么来的呢?看看一个注册led设备类的函数.[cpp] view plain copy print ?
- /**
- *led_classdev_register-registeranewobjectofled_classdevclass.
- *@parent:Thedevicetoregister.
- *@led_cdev:theled_classdevstructureforthisdevice.
- */
- intled_classdev_register(structdevice*parent,structled_classdev*led_cdev)
- {
- led_cdev->dev=device_create(leds_class,parent,0,led_cdev,
- "%s",led_cdev->name);
- if(IS_ERR(led_cdev->dev))
- returnPTR_ERR(led_cdev->dev);
- #ifdefCONFIG_LEDS_TRIGGERS
- init_rwsem(&led_cdev->trigger_lock);
- ...
/** * led_classdev_register - register a new object of led_classdev class. * @parent: The device to register. * @led_cdev: the led_classdev structure for this device. */int led_classdev_register(struct device *parent, struct led_classdev *led_cdev){led_cdev->dev = device_create(leds_class, parent, 0, led_cdev, "%s", led_cdev->name);if (IS_ERR(led_cdev->dev))return PTR_ERR(led_cdev->dev);#ifdef CONFIG_LEDS_TRIGGERSinit_rwsem(&led_cdev->trigger_lock);...这个注册函数的接口最终会被我们要开发的背光驱动调用,这个接口在/sys/class/leds/下又创建了一个设备接口,名字是led_cdev->name。好明显这里的led_cdev->name应该就是”lcd-backlight“,究竟是不是真的这样呢?继续看。这个led-class.c在实现两个设备属性,看代码:[cpp] view plain copy print ?
- staticstructdevice_attributeled_class_attrs[]={
- __ATTR(brightness,0644,led_brightness_show,led_brightness_store),
- __ATTR(max_brightness,0444,led_max_brightness_show,NULL),
- #ifdefCONFIG_LEDS_TRIGGERS
- __ATTR(trigger,0644,led_trigger_show,led_trigger_store),
- #endif
- __ATTR_NULL,
- };
static struct device_attribute led_class_attrs[] = {__ATTR(brightness, 0644, led_brightness_show, led_brightness_store),__ATTR(max_brightness, 0444, led_max_brightness_show, NULL),#ifdef CONFIG_LEDS_TRIGGERS__ATTR(trigger, 0644, led_trigger_show, led_trigger_store),#endif__ATTR_NULL,};看到了属性名字为”brightness“,这似乎越来越接近解释"/sys/class/leds/lcd-backlight/brightness"的由来了。
5.Linux的背光驱动层
Linux的背光驱动层就是完全由开发者去实现了,其实这层很简单,无非就是通过pwm实现设置背光。在这一层要注意将背光亮度量化为0~255,这是Android上层约定的。这一层的采用Linux的platform device/driver 模型。它最终会调用Linux内核层leds-class.c的接口。看看它的probe函数片段:[cpp] view plain copy print ?
- structdisplay_led_data{
- structled_classdevpri_display_class_dev;
- structled_classdevsec_display_class_dev;
- structomap4_disp_led_platform_data*led_pdata;
- structmutexpri_disp_lock;
- structmutexsec_disp_lock;
- };
- staticintomap4_XXX_display_probe(structplatform_device*pdev)
- {
- intret;
- structdisplay_led_data*info;
- pr_info("%s:Enter\n",__func__);
- if(pdev->dev.platform_data==NULL){
- pr_err("%s:platformdatarequired\n",__func__);
- return-ENODEV;
- }
- info=kzalloc(sizeof(structdisplay_led_data),GFP_KERNEL);
- if(info==NULL){
- ret=-ENOMEM;
- returnret;
- }
- info->led_pdata=pdev->dev.platform_data;
- platform_set_drvdata(pdev,info);
- info->pri_display_class_dev.name="lcd-backlight";
- info->pri_display_class_dev.brightness_set=omap4_xxx_primary_disp_store;
- ...
- ret=led_classdev_register(&pdev->dev,
- &info->pri_display_class_dev);
- if(ret<0){
- pr_err("%s:Registerledclassfailed\n",__func__);
- kfree(info);
- returnret;
- }
- if(info->led_pdata->flags&LEDS_CTRL_AS_TWO_DISPLAYS){
- pr_info("%s:ConfiguringthesecondaryLED\n",__func__);
- info->sec_display_class_dev.name="lcd-backlight2";
- info->sec_display_class_dev.brightness_set=
- omap4_mirage_secondary_disp_store;
- info->sec_display_class_dev.max_brightness=LED_OFF;
- mutex_init(&info->sec_disp_lock);
- ret=led_classdev_register(&pdev->dev,
- &info->sec_display_class_dev);
- ...
struct display_led_data {struct led_classdev pri_display_class_dev;struct led_classdev sec_display_class_dev;struct omap4_disp_led_platform_data *led_pdata;struct mutex pri_disp_lock;struct mutex sec_disp_lock;};static int omap4_XXX_display_probe(struct platform_device *pdev){int ret;struct display_led_data *info;pr_info("%s:Enter\n", __func__);if (pdev->dev.platform_data == NULL) {pr_err("%s: platform data required\n", __func__);return -ENODEV;}info = kzalloc(sizeof(struct display_led_data), GFP_KERNEL);if (info == NULL) {ret = -ENOMEM;return ret;}info->led_pdata = pdev->dev.platform_data;platform_set_drvdata(pdev, info);info->pri_display_class_dev.name = "lcd-backlight";info->pri_display_class_dev.brightness_set = omap4_xxx_primary_disp_store;...ret = led_classdev_register(&pdev->dev, &info->pri_display_class_dev);if (ret < 0) {pr_err("%s: Register led class failed\n", __func__);kfree(info);return ret;}if (info->led_pdata->flags & LEDS_CTRL_AS_TWO_DISPLAYS) {pr_info("%s: Configuring the secondary LED\n", __func__);info->sec_display_class_dev.name = "lcd-backlight2";info->sec_display_class_dev.brightness_set =omap4_mirage_secondary_disp_store;info->sec_display_class_dev.max_brightness = LED_OFF;mutex_init(&info->sec_disp_lock);ret = led_classdev_register(&pdev->dev, &info->sec_display_class_dev);...
需关注这里设置了info->pri_display_class_dev.name = "lcd-backlight";,然后调用led_classdev_register函数注册,所以完美解释了led_cdev->name就是"lcd-backlight",完美解释了"/sys/class/leds/lcd-backlight/brightness"的由来。
另外info->pri_display_class_dev.brightness_set = omap4_xxx_primary_disp_store;中的omap4_xxx_primary_disp_store()就是我们需要实现的设置背光亮度函数,函数里面就是pwm操作。到这里又有一个疑问4:为什么只实现设置背光亮度的接口,而没有实现读取当前亮度量化值的接口?其实Android上层自行处理了这个获取亮度量化值的事情,也就是说Android上层设置了亮度是多少,上层会执行保留设置结果。无需再通过下层读取。
6.总结
6.1针对之前的疑问1/2,其实LCD背光的sys接口路径是可以改的,但是需要Linux内核层和Android HAL层配合来改,单单改一方都是会导致Android Setting无法调节背光。6.2需注意在实现Linux背光驱动时的亮度量化关系,也就是注意上层传递下来的亮度设置范围是0~255。6.3Android底层的Linux驱动都是服务于上层Java的,在做Android底层的Linux驱动时需要明确和上层的接口依赖关系,否则无法重用google或芯片厂商实现的接口,从而导致功能无法用。6.4.再一次证明了Android系统服务运行效率极低。设置背光,其实最终就是设置了一下pwm寄存器即可,但是从Android最顶层一层层调用下来,真是“费尽周折”,怪不得Android设备的硬件配置明显远优于ios设备,但是流畅体验性却不明显优于ios设备。更多相关文章
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