OMAP Power Management

PM branch

The PM branch is a developement branch of the linux-omap kernel for the purposes of developing and stabilizing the PM infrastructure for OMAP and submitting it upstream.

The maintainer of the PM branch is Kevin Hilman.

Features

• full-chip retention in idle and suspend
• full-chip OFF in idle and suspend
• idle PM via CPUidle
• support for multiple OMAP3/4 boards

The latest, tested PM branch is available as a branch named 'pm' from the linux-omap-pm repository. This branch is also sync'd daily as the 'pm' branch of the main linux-omap repository.

Current version

Supported platforms (OMAP3 only)

Tested on the following platforms using omap3_pm_defconfig with busybox-based initramfs, and tested full-chip RET and OFF in idle and suspend:

• 3430SDP
• OMAP3EVM
• Beagle
• Overo (Water + Tobi)
• Nokia N900 (a.k.a RX51)
• Zoom2
• KwikByte KBOC

Using OMAP PM

Features

By default, the OMAP is configured to hit full-chip retention in suspend.

Suspend/Resume

# echo mem > /sys/power/state

Serial console activity or other configured wakeup sources (keypad, touchscreen) will trigger resume.

Upon resume, you can use the powerdomain state statistics to check whether all states hit the desired state, cf. 'Debug info'

# cat /debug/pm_debug/count

In addition, if any power domains did not hit the desired state, you will see a message on the console.

Enabling system for hitting retention during idle

By default, the UARTs will not automatically idle when unused so they will prevent low-power states during idle. To enable UART idle timeouts with a 5 second timeout:

# echo 5 > /sys/devices/platform/omap/omap_uart.0/sleep_timeout               
# echo 5 > /sys/devices/platform/omap/omap_uart.1/sleep_timeout               
# echo 5 > /sys/devices/platform/omap/omap_uart.2/sleep_timeout               
# echo 5 > /sys/devices/platform/omap/omap_uart.3/sleep_timeout               

NOTE: the 4th UART is only present on 3630 and OMAP4.

Then, wait for any inactivity timers to expire (such as the 5 second UART timer) and check the powerdomain transition statistics to see that transitions are happening

 # cat /debug/pm_debug/count

Enabling system for hitting OFF

By default, retention is the deepest sleep state attempted. To enable power domain transitions to off mode

# echo 1 > /debug/pm_debug/enable_off_mode

Once again, after a suspend or after some idle time, use the power domain transition stats to check that transitions to off-mode are happening

 # cat /debug/pm_debug/count

Known Problems

• Zoom2/3: serial console wakeups not working
  • Problem: on suspend, by default the serial driver will disable serial interrupts, thus disabling the GPIO IRQ needed for wakeup.
  • Fix: enable the wakeup feature for the tty used as console:

 # echo enabled > /sys/devices/platform/serial8250.0/tty/ttyS0/power/wakeup 

• GPIO module-level wakeups not always working
  • Background: GPIO wakeups can happen either via the GPIO module itself (module-level wakeups) or via IO pad wakeups if the CORE powerdomain is inactive, in retention or off.
  • If the IO pad wakeups are not enabled (either because CORE remains on, or because IO pad is not armed) GPIO wakeups may not happen unless the GPIO module-level wakeups are programmed correctly.
  • To ensure GPIO module wakeups are programmed correctly:
    • Enable GPIO IRQ for wakeup GPIO, including ISR. Use request_irq()
    • Ensure GPIO is edge-triggered. Only edge triggered GPIOs are wakeup capable (c.f. omap34xx TRM Sec. 25.5.3.1)
      • the flags argument of request_irq() should have either IRQF_TRIGGER_FALLING, IRQF_TRIGGER_RISING or both.
    • Enable GPIO IRQ as wakeup source using enable_irq_wake(gpio_to_irq(<gpio>))
  • NOTE: It is very important that an interrupt handler be configured for the GPIO IRQ, even if it does nothing but return IRQ_HANDLED. This is because without an interrupt handler, the GPIO IRQ event will never be properly cleared and this can prevent the GPIO module from hitting retention or off on the next idle request (c.f. omap34xx TRM Sec. 25.5.3.1).

• GPIO wakeup works once, but prevents future retention
  • See NOTE just above

Advanced features for PM developers and power users

Debug info

First, mount the debug filesystem (debugfs)

# mount -t debugfs debugfs /debug

Show powerdomain state statistics and clockdomain active clocks

# cat /debug/pm_debug/count

This will look something like this on OMAP3:

 # cat /debug/pm_debug/count
 cefuse_pwrdm (OFF),OFF:1,RET:0,INA:0,ON:0,RET-LOGIC-OFF:0
 always_on_core_pwrdm (OFF),OFF:1,RET:0,INA:0,ON:0,RET-LOGIC-OFF:0
 l4per_pwrdm (ON),OFF:0,RET:0,INA:0,ON:1,RET-LOGIC-OFF:0,RET-MEMBANK1-OFF:0,RET-MEMBANK2-OFF:0
 l3init_pwrdm (RET),OFF:0,RET:1,INA:0,ON:1,RET-LOGIC-OFF:0,RET-MEMBANK1-OFF:0
 cam_pwrdm (OFF),OFF:1,RET:0,INA:0,ON:0,RET-LOGIC-OFF:0,RET-MEMBANK1-OFF:0
 ivahd_pwrdm (RET),OFF:1,RET:1,INA:0,ON:1,RET-LOGIC-OFF:0,RET-MEMBANK1-OFF:0,RET-MEMBANK2-OFF:0,RET-MEMBANK3-OFF:0,RET-MEMBANK4-OFF:0
 mpu_pwrdm (ON),OFF:0,RET:0,INA:0,ON:1,RET-LOGIC-OFF:0,RET-MEMBANK1-OFF:0,RET-MEMBANK2-OFF:0
 cpu1_pwrdm (ON),OFF:0,RET:0,INA:0,ON:1,RET-LOGIC-OFF:0,RET-MEMBANK1-OFF:0
 cpu0_pwrdm (ON),OFF:0,RET:0,INA:0,ON:1,RET-LOGIC-OFF:0,RET-MEMBANK1-OFF:0
 tesla_pwrdm (RET),OFF:1,RET:1,INA:0,ON:0,RET-LOGIC-OFF:0,RET-MEMBANK1-OFF:0,RET-MEMBANK2-OFF:0,RET-MEMBANK3-OFF:0
 dss_pwrdm (RET),OFF:0,RET:1,INA:0,ON:1,RET-LOGIC-OFF:0,RET-MEMBANK1-OFF:0
 abe_pwrdm (ON),OFF:1,RET:0,INA:0,ON:1,RET-LOGIC-OFF:0,RET-MEMBANK1-OFF:0,RET-MEMBANK2-OFF:0
 gfx_pwrdm (OFF),OFF:2,RET:0,INA:0,ON:1,RET-LOGIC-OFF:0,RET-MEMBANK1-OFF:0
 core_pwrdm (ON),OFF:0,RET:0,INA:0,ON:1,RET-LOGIC-OFF:0,RET-MEMBANK1-OFF:0,RET-MEMBANK2-OFF:0,RET-MEMBANK3-OFF:0,RET-MEMBANK4-OFF:0,RET-MEMBANK5-OFF:0

If you see each power domain has counters specified. OFF, RET, INA and so on...The count basically keeps incrementing every time it hits low power state. In the above example, cam_pwrdm (camera power domain) has hit OFF state once. GFX power domain has hit OFF state twice and like wise.

UART wakeup and timeout options

By default, each of the on-chip OMAP UARTs are enabled as wakeup sources. In addition, they are configured with a configurable inactivity timer (default 5 seconds) after which the UART clocks are allowed to be gated during idle or suspend.

For example, to disable the wakeup capability of a UART1 (a.k.a ttyO0)

 # echo disabled > /sys/devices/platform/omap/omap-hsuart.0/power/wakeup

And to change the inactivity timer to 10 seconds, instead of the default 5:

 # echo 10 > /sys/devices/platform/omap/omap-hsuart.0/sleep_timeout

Note that you can cat these files under /sys as well to see the current values.

UART PM Debugging Techniques

Debugging problems with the OMAP UART driver wakeup and data transfer when Power Management is enabled can be quite tedious, if one does not have a proper HW setup. An example of a setup (including both HW and SW changes) can be found in the OMAP_UART_pm_debugging page.

Public Power management test framework

Some commonly used power management utilities are listed here which make sense from an OMAP perspective

Cpufreq utils

cpufreq utils for testing dynamic voltage and frequency scaling.

Maemo pm_test

pm-test plugin for Maemo says

 utility which tests that kernel and kernel modules works power management wise

This utility could be used to sanity test the powermanagement impact to a system for suspend/restore and basic power features.

Quick verification of suspend-idle functionality

the following script may be used with userspace supporting something simple as busybox:

#!/bin/ash
# Quick script to verify SUSPEND Resume behavior without human intervention
# Refer: http://elinux.org/OMAP_Power_Management for details

# Some params that might change based on the environment
SYS=/sys
DEBUG=$SYS/kernel/debug
PROC=/proc

PMDEBUG=$DEBUG/pm_debug
VOLTAGE_OFF=$PMDEBUG/voltage_off_mode
kver=`uname -r`
if [ $kver > "2.6.36" ]; then
	UART="$SYS/devices/platform/omap/omap-hsuart"
else
	UART="$SYS/devices/platform/serial8250"
fi
UART1=$UART.0/sleep_timeout
UART2=$UART.1/sleep_timeout
UART3=$UART.2/sleep_timeout

# Setup cpu idle
cpu_idle(){
	echo -n "$1" > $PMDEBUG/sleep_while_idle
}

# setup off mode
off_mode(){
	echo -n "$1" > $PMDEBUG/enable_off_mode
}

# Do a suspend
suspend_me(){
	echo -n "mem" > $SYS/power/state
}

# get my core data (This is the last domain to hit lowest power state)
core_count(){
	cat $PMDEBUG/count |grep "^core_pwrdm"
}

# get my retention counter
core_ret_count(){
	core_count|cut -d ',' -f3|cut -d ':' -f2
}

# get my off counter
core_off_count(){
	core_count|cut -d ',' -f2|cut -d ':' -f2
}

# setup wakeup timer - automated testing
wakeup_timer(){
	echo -n "$1" > $PMDEBUG/wakeup_timer_seconds
	echo -n "$2" > $PMDEBUG/wakeup_timer_milliseconds
}

# Setup our uart to be inactivity timer
setup_tty_sleep_timeout() {
	if [ -f $UART1 ]; then
		echo -n "$1" > $UART1
	fi
	if [ -f $UART2 ]; then
		echo -n "$1" > $UART1
	fi
	if [ -f $UART3 ]; then
		echo -n "$1" > $UART3
	fi

}

# Measurement Start
measure_start(){
	OFF_START=`core_off_count`
	RET_START=`core_ret_count`
	TIME_START=`date "+%s"`
}
# Measurement End
measure_end(){
	OFF_END=`core_off_count`
	RET_END=`core_ret_count`
	TIME_END=`date "+%s"`
}
# Common formatted print
measure_print(){
	DUR=`expr $TIME_END - $TIME_START`
	echo "$1 | $2 | OFF: $OFF_START->$OFF_END| RET:$RET_START->$RET_END ($DUR sec)"
}

# verify function
check_core_off(){
	RESULT=FAIL
	if [ $OFF_START -lt $OFF_END ]; then
		RESULT=PASS
	fi
}
check_core_ret(){
	RESULT=FAIL
	if [ $RET_START -lt $RET_END ]; then
		RESULT=PASS
	fi
}

# Disable everything
disable_all(){
	# disable voltage off
	if [ -f $VOLTAGE_OFF ]; then
		echo -n "0" >$VOLTAGE_OFF
	fi
	setup_tty_sleep_timeout 0
	wakeup_timer 0 0
	off_mode 0
	cpu_idle 0
}

# test idle - core ret
test_idle_ret() {
	disable_all
	measure_start
	setup_tty_sleep_timeout 5
	cpu_idle 1
	sleep 20
	disable_all
	sleep 1;sync
	measure_end
	check_core_ret
	measure_print "IDLE:RET test" $RESULT
}

# test idle - core off
test_idle_off() {
	disable_all
	measure_start
	setup_tty_sleep_timeout 5
	off_mode 1
	cpu_idle 1
	sleep 20
	disable_all
	sleep 1;sync
	measure_end
	check_core_off
	measure_print "IDLE:OFF test" $RESULT
}

# test suspend - core ret
test_suspend_ret() {
	disable_all
	measure_start
	wakeup_timer 5 0
	suspend_me
	disable_all
	sleep 1;sync
	measure_end
	check_core_ret
	measure_print "SUSPEND:RET test" $RESULT
}

# test suspend - core off
test_suspend_off() {
	disable_all
	measure_start
	off_mode 1
	wakeup_timer 5 0
	suspend_me
	disable_all
	sleep 1;sync
	measure_end
	check_core_off
	measure_print "SUSPEND:OFF test" $RESULT
}

# mount up the basic fs
already_mntd=`mount|grep $PROC`
if [ x == x"$already_mntd" ]; then
	mount -t proc none $PROC
fi

already_mntd=`mount|grep $SYS`
if [ x == x"$already_mntd" ]; then
	mount -t sysfs none $SYS
fi
already_mntd=`mount|grep $DEBUG`
if [ x == x"$already_mntd" ]; then
	mount -t debugfs none $DEBUG
fi
# Lets run the tests one by one..
NR=""
R=`test_suspend_off`
echo $R
NR="$NR\n$R"
R=`test_suspend_ret`
echo $R
NR="$NR\n$R"
R=`test_idle_off`
echo $R
NR="$NR\n$R"
R=`test_idle_ret`
echo $R
NR="$NR\n$R"
# Print End result summary
cat $PMDEBUG/count

# Print test summary
echo -e "$NR"