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- How to get s2ram working
- ~~~~~~~~~~~~~~~~~~~~~~~~
- 2006 Linus Torvalds
- 2006 Pavel Machek
-1) Check, 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.
- ~~~~~~~~~~~~~~~~~~
-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.
-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.