Android Power Management on i.MX6DQ/DL | Freescale Community

老匹夫 2015-06-16

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Android Power Debug and Optimization

Introduction
Android Power Management on i.MX Overview
How to do power optimization for Android on i.MX
How to check high power consumption on i.MX
How to debug suspend/resume problems on i.MX

Introduction

This document describes i.MX Android power issues debug and power consumption optimization.

Android Power Management on i.MX Overview

What Power Manager introduced by Android

· Early Suspend

It is allow drivers like LCD, keypad backlight, touch-screen, gsensor, to be notified when user-space writes to /sys/power/request_state to indicate that the user visible sleep state should change. These drivers will act as like Linux stand suspend() to let these devices entry in suspend for better battery life.

·Late Resume

Late resume is matching with early suspend. It will resume the devices suspended during early suspend after the Stand Linux resume finished

·Wake Locks

Wake locks are used by applications, services, kernel drivers to request CPU resources. A locked wakelock, depending on its type, prevents the system from entering suspend or other low-power states. It as a core member in android power management architecture from framework to kernel

What introduced by i.MX to enhance the power framework

BusFreq
- Support High bus, Low power audio bus and Low bus totally 3 system bus working points.
- Switching between these 3 bus mode according clock flags automatically.
- DDR running frequency will change according bus mode changing (highest 528/400MHz and lowest at 24MHz for MX6DQ/DL).
CPUFreq
- The CPU frequency scaling device driver allows the clock speed of the CPUs to be changed on the fly. Once the CPU frequency is changed, the GP voltage will be changed to the voltage value.
- Enhance the default interactive governor for better performance on SDHC/GPU etc.
System Power Profile Service and App (just for MX6DQ/DL)
- Support 3 profiles currently: Normal mode, Power Saving Mode and Performance Mode to get much better balance between performance and power consumption.
- Profiles can be customized according customers’ HW /MD design, including: CPU running max freq, trigger temperature, CPU running minimal freq, running cpu
LDO bypass mode

i.MX6X has built-in LDO module, but also allows you to use external LDO suppliers. SW will provide the configuration using external LDO or internal LDO.

How to do power optimization for Android on i.MX

Suspend Mode

All devices enter in suspend or low power
Config GPIO PADs as High Z or input mode (depending on HW design,FSL provide Ref code)
Cut off LDOs which no modules need (depending on HW design, FSL provide Ref code)
DDR enter in self-refresh mode (FSL done)
Config DDR IO Float pin to reduce the DDR IO consumption (FSL done)
ARM core entry stop mode (WFI) (FSL done)
All PLLs will cut off, just 32KHZ sleep clock living (FSL done)
Notify the PMIC entry in standby to save some power (FSL done)

User Idle Mode

Optimization on device driver for WiFi, 3G, BT, screen brightness modules, etc., to save some power
Let some device/GPIOs entry in suspend mode/low power mode
Active power saving profile to reduce some system power loading.
GPU 2D/3D auto entry in Stop/Standby mode if no activity needs update. (FSL done)
Enable CPUFreq reduce ARM CORE power consumption (FSL done)
Busfreq scanning to let system work at lower Freq to save power (FSL done)

Audio/Video Playback Mode

Optimization on device driver for WiFi, 3G, BT, screen brightness modules, etc., to save some power
Let some device/GPIOs entry in suspend mode/low power mode
Disable HW 3D acceleration for some Apps such as System UI, Music Player, etc., to save some power when System in IDLE or music playing mode.
Enable CPUFreq and SOC WAIT mode, decrease CPU Freq/Voltage to save power for ARM CORE when no there is no task need cpu to handle(FSL done)
Busfreq scanning will set bus work at low power audio bus mode to save some power (FSL done for audio case)
DDR enter in self-refresh mode (FSL done for audio case)
Reduce the screen brightness will save some power (for video case)
VPU clock auto-gating to save power on SOC domain (for video case, FSL done)
GPU 2D/3D auto-gating to save some power on SOC domain (FSL done)
Try VDOA+IPU to bypass GPU in video playback(not comment for Android platform, pure Linux environment using this method, for it has some limitation such as the input/output size limit), this can save some power on DDR domain.

How to check high power consumption on i.MX

Idle Audio/Video Playback high power consumption

Check the CPUFreq and Bus_freq is enabled

cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor

cat /sys/devices/platform/imx_busfreq.0/enable

Check whether the system bus working poing
For MX6Q:

cat /sys/kernel/debug/clock/osc_clk/pll2_528_bus_main_clk/periph_clk/mmdc_ch0_axi_clk/rate

For MX6DL/SL:

cat /sys/kernel/debug/clock/osc_clk/pll2_528_bus_main_clk/pll2_pfd_400M/periph_clk/mmdc_ch0_axi_clk/rate

Check CPU Loading and Interrupt(cat /proc/interrupts)
Check clock tree carefully to see which clocks arenot gated off but no any modules need them.

powerdebug –d -c

SUSPEND MODE high power consumption

Make sure all device entries are in suspend mode
Make sure the system entry in DSM(measure the voltage &current of VDDARM_CAP, VDDSOC_CAP,DDR_1V5, VDD_HIGH…)

Some tips help to locate the problems

Add debug message in device drivers which may lead high power consumption
Enable PM debug in kernel
Catch the waveform from these modules which may impact the high power consumption
Remove devices from the board or do H/W rework to exclude some H/W problems