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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:
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
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.
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.