From 849369d6c66d3054688672f97d31fceb8e8230fb Mon Sep 17 00:00:00 2001 From: root Date: Fri, 25 Dec 2015 04:40:36 +0000 Subject: initial_commit --- Documentation/power/s2ram.txt | 81 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 81 insertions(+) create mode 100644 Documentation/power/s2ram.txt (limited to 'Documentation/power/s2ram.txt') diff --git a/Documentation/power/s2ram.txt b/Documentation/power/s2ram.txt new file mode 100644 index 00000000..1bdfa044 --- /dev/null +++ b/Documentation/power/s2ram.txt @@ -0,0 +1,81 @@ + How to get s2ram working + ~~~~~~~~~~~~~~~~~~~~~~~~ + 2006 Linus Torvalds + 2006 Pavel Machek + +1) Check suspend.sf.net, program s2ram there has long whitelist of + "known ok" machines, along with tricks to use on each one. + +2) If that does not help, try reading tricks.txt and + video.txt. Perhaps problem is as simple as broken module, and + simple module unload can fix it. + +3) You can use Linus' TRACE_RESUME infrastructure, described below. + + Using TRACE_RESUME + ~~~~~~~~~~~~~~~~~~ + +I've been working at making the machines I have able to STR, and almost +always it's a driver that is buggy. Thank God for the suspend/resume +debugging - the thing that Chuck tried to disable. That's often the _only_ +way to debug these things, and it's actually pretty powerful (but +time-consuming - having to insert TRACE_RESUME() markers into the device +driver that doesn't resume and recompile and reboot). + +Anyway, the way to debug this for people who are interested (have a +machine that doesn't boot) is: + + - enable PM_DEBUG, and PM_TRACE + + - use a script like this: + + #!/bin/sh + sync + echo 1 > /sys/power/pm_trace + echo mem > /sys/power/state + + to suspend + + - if it doesn't come back up (which is usually the problem), reboot by + holding the power button down, and look at the dmesg output for things + like + + Magic number: 4:156:725 + hash matches drivers/base/power/resume.c:28 + hash matches device 0000:01:00.0 + + which means that the last trace event was just before trying to resume + device 0000:01:00.0. Then figure out what driver is controlling that + device (lspci and /sys/devices/pci* is your friend), and see if you can + fix it, disable it, or trace into its resume function. + + If no device matches the hash (or any matches appear to be false positives), + the culprit may be a device from a loadable kernel module that is not loaded + until after the hash is checked. You can check the hash against the current + devices again after more modules are loaded using sysfs: + + cat /sys/power/pm_trace_dev_match + +For example, the above happens to be the VGA device on my EVO, which I +used to run with "radeonfb" (it's an ATI Radeon mobility). It turns out +that "radeonfb" simply cannot resume that device - it tries to set the +PLL's, and it just _hangs_. Using the regular VGA console and letting X +resume it instead works fine. + +NOTE +==== +pm_trace uses the system's Real Time Clock (RTC) to save the magic number. +Reason for this is that the RTC is the only reliably available piece of +hardware during resume operations where a value can be set that will +survive a reboot. + +Consequence is that after a resume (even if it is successful) your system +clock will have a value corresponding to the magic number instead of the +correct date/time! It is therefore advisable to use a program like ntp-date +or rdate to reset the correct date/time from an external time source when +using this trace option. + +As the clock keeps ticking it is also essential that the reboot is done +quickly after the resume failure. The trace option does not use the seconds +or the low order bits of the minutes of the RTC, but a too long delay will +corrupt the magic value. -- cgit v1.2.3