Android虚拟电源管理驱动

Android系统如果没有电源管理相关的驱动程序，在启动时将会提示如下错误：

I/SystemServer(   50): Starting Battery Service.
E/BatteryService(   50): Could not open '/sys/class/power_supply/ac/online'
E/BatteryService(   50): Could not open '/sys/class/power_supply/usb/online'
E/BatteryService(   50): Could not open '/sys/class/power_supply/battery/present'
E/BatteryService(   50): Could not open '/sys/class/power_supply/battery/capacity'
E/BatteryService(   50): Could not open '/sys/class/power_supply/battery/batt_vol'
E/BatteryService(   50): Could not open '/sys/class/power_supply/battery/batt_temp'
E/BatteryService(   50): Could not open '/sys/class/power_supply/battery/status'
E/BatteryService(   50): Could not open '/sys/class/power_supply/battery/health'
E/BatteryService(   50): Could not open '/sys/class/power_supply/battery/technology'
I/SystemServer(   50): Starting Hardware Service.

此时启动完成后将显示Poweroff界面
图1

图2

这个问题的原因很简单，因为缺少相关电源部分驱动程序，Android系统无法获取/sys/class/power_supply/下的信息，从而导致启动不能。

对于开发板，开发的初期一般没有电源管理驱动程序，那要如何解决这个问题呢？

网上流传的解决办法是通过修改Android源码中的com_android_server_BatteryService.cpp，让android系统不去去读相关信息，强行赋值为电量充足。

但是如果无法重新编译android文件系统，应该如何处理？

其实，有一个更好的解决方法，就是在Linux内核中写一个虚拟电源驱动，这样的好处是增加电源芯片后，直接在此驱动上修改即可，也不用修改Android源码了。

/sys/class # cd power_supply/
/sys/class/power_supply # ls
ac       battery
/sys/class/power_supply # cd battery/
/sys/class/power_supply/battery # ls
capacity        manufacturer    subsystem       uevent
charge_counter power           technology      voltage_avg
current_avg     present         temp
device          serial_number   temp_ambient
health          status          type
/sys/class/power_supply/battery #

驱动源码：
=========================================================================================================
/*
* Fake Battery driver for android
*
* Copyright © 2009 Rockie Cheng < [e-mail] >
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/

#include <linux/module.h>
#include <linux/err.h>
#include <linux/platform_device.h>
#include <linux/power_supply.h>
#include <linux/jiffies.h>
#include <linux/sched.h>

#define BAT_STAT_PRESENT 0x01
#define BAT_STAT_FULL   0x02
#define BAT_STAT_LOW   0x04
#define BAT_STAT_DESTROY 0x08
#define BAT_STAT_AC   0x10
#define BAT_STAT_CHARGING 0x20
#define BAT_STAT_DISCHARGING 0x40

#define BAT_ERR_INFOFAIL 0x02
#define BAT_ERR_OVERVOLTAGE 0x04
#define BAT_ERR_OVERTEMP 0x05
#define BAT_ERR_GAUGESTOP 0x06
#define BAT_ERR_OUT_OF_CONTROL 0x07
#define BAT_ERR_ID_FAIL   0x09
#define BAT_ERR_ACR_FAIL 0x10

#define BAT_ADDR_MFR_TYPE 0x5F

static int android_ac_get_prop(struct power_supply *psy,
enum power_supply_property psp,
union power_supply_propval *val)
{

switch (psp)
{
case POWER_SUPPLY_PROP_ONLINE:
val->intval = BAT_STAT_AC;
break;
default:
break;
}
return 0;
}

static enum power_supply_property android_ac_props[] =
{
POWER_SUPPLY_PROP_ONLINE,
};

static struct power_supply android_ac =
{
.name = "ac",
.type = POWER_SUPPLY_TYPE_MAINS,
.properties = android_ac_props,
.num_properties = ARRAY_SIZE(android_ac_props),
.get_property = android_ac_get_prop,
};

static int android_bat_get_status(union power_supply_propval *val)
{

val->intval = POWER_SUPPLY_STATUS_FULL;
return 0;
}

static int android_bat_get_health(union power_supply_propval *val)
{

val->intval = POWER_SUPPLY_HEALTH_GOOD;
return 0;
}

static int android_bat_get_mfr(union power_supply_propval *val)
{

val->strval = "Rockie";
return 0;
}

static int android_bat_get_tech(union power_supply_propval *val)
{
val->intval = POWER_SUPPLY_TECHNOLOGY_LION;
return 0;
}

static int android_bat_get_property(struct power_supply *psy,
enum power_supply_property psp,
union power_supply_propval *val)
{
int ret = 0;

switch (psp)
{
case POWER_SUPPLY_PROP_STATUS:
ret = android_bat_get_status(val);
if (ret)
return ret;
break;
case POWER_SUPPLY_PROP_PRESENT:
val->intval = BAT_STAT_PRESENT;
break;

case POWER_SUPPLY_PROP_HEALTH:
ret = android_bat_get_health(val);
break;
case POWER_SUPPLY_PROP_MANUFACTURER:
ret = android_bat_get_mfr(val);
if (ret)
return ret;
break;
case POWER_SUPPLY_PROP_TECHNOLOGY:
ret = android_bat_get_tech(val);
if (ret)
return ret;
break;
case POWER_SUPPLY_PROP_VOLTAGE_AVG:
val->intval = 3;
break;
case POWER_SUPPLY_PROP_CURRENT_AVG:
val->intval = 3;
break;
case POWER_SUPPLY_PROP_CAPACITY:
val->intval = 100;
break;
case POWER_SUPPLY_PROP_TEMP:
val->intval = 50;
break;
case POWER_SUPPLY_PROP_TEMP_AMBIENT:
val->intval = 50;
break;
case POWER_SUPPLY_PROP_CHARGE_COUNTER:
val->intval = 10;
break;
case POWER_SUPPLY_PROP_SERIAL_NUMBER:
break;
default:
ret = -EINVAL;
break;
}
return ret;
}

static enum power_supply_property android_bat_props[] = {
POWER_SUPPLY_PROP_STATUS,
POWER_SUPPLY_PROP_PRESENT,
POWER_SUPPLY_PROP_HEALTH,
POWER_SUPPLY_PROP_TECHNOLOGY,
POWER_SUPPLY_PROP_VOLTAGE_AVG,
POWER_SUPPLY_PROP_CURRENT_AVG,
POWER_SUPPLY_PROP_CAPACITY,
POWER_SUPPLY_PROP_TEMP,
POWER_SUPPLY_PROP_TEMP_AMBIENT,
POWER_SUPPLY_PROP_MANUFACTURER,
POWER_SUPPLY_PROP_SERIAL_NUMBER,
POWER_SUPPLY_PROP_CHARGE_COUNTER,
};

/*********************************************************************
*   Initialisation
*********************************************************************/

static struct platform_device *bat_pdev;

static struct power_supply android_bat =
{
.properties = android_bat_props,
.num_properties = ARRAY_SIZE(android_bat_props),
.get_property = android_bat_get_property,
.use_for_apm = 1,
};

 

static int __init android_bat_init(void)
{
int ret = 0;

bat_pdev = platform_device_register_simple("battery", 0, NULL, 0);

ret = power_supply_register(&bat_pdev->dev, &android_ac);
if (ret)
goto ac_failed;

android_bat.name = bat_pdev->name;

ret = power_supply_register(&bat_pdev->dev, &android_bat);
if (ret)
goto battery_failed;

goto success;

power_supply_unregister(&android_bat);
battery_failed:
power_supply_unregister(&android_ac);
ac_failed:
platform_device_unregister(bat_pdev);
success:
return ret;
}

static void __exit android_bat_exit(void)
{
power_supply_unregister(&android_bat);
power_supply_unregister(&android_ac);
platform_device_unregister(bat_pdev);
}

module_init(android_bat_init);
module_exit(android_bat_exit);

MODULE_AUTHOR("Rockie Cheng < [e-mail] >");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Fake Battery driver for android");