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If the device which fails to resume is part of a loadable kernel module it won't be checked at startup against the magic number stored in the RTC. Add a read-only sysfs attribute /sys/power/pm_trace_dev_match which contains a list of newline separated devices (usually just the one) which currently match the last magic number. This allows the device which is failing to resume to be found after the modules are loaded again. Signed-off-by: James Hogan <james@albanarts.com> Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
82 lines
3.1 KiB
Plaintext
82 lines
3.1 KiB
Plaintext
How to get s2ram working
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~~~~~~~~~~~~~~~~~~~~~~~~
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2006 Linus Torvalds
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2006 Pavel Machek
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1) Check suspend.sf.net, program s2ram there has long whitelist of
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"known ok" machines, along with tricks to use on each one.
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2) If that does not help, try reading tricks.txt and
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video.txt. Perhaps problem is as simple as broken module, and
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simple module unload can fix it.
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3) You can use Linus' TRACE_RESUME infrastructure, described below.
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Using TRACE_RESUME
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~~~~~~~~~~~~~~~~~~
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I've been working at making the machines I have able to STR, and almost
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always it's a driver that is buggy. Thank God for the suspend/resume
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debugging - the thing that Chuck tried to disable. That's often the _only_
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way to debug these things, and it's actually pretty powerful (but
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time-consuming - having to insert TRACE_RESUME() markers into the device
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driver that doesn't resume and recompile and reboot).
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Anyway, the way to debug this for people who are interested (have a
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machine that doesn't boot) is:
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- enable PM_DEBUG, and PM_TRACE
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- use a script like this:
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#!/bin/sh
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sync
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echo 1 > /sys/power/pm_trace
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echo mem > /sys/power/state
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to suspend
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- if it doesn't come back up (which is usually the problem), reboot by
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holding the power button down, and look at the dmesg output for things
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like
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Magic number: 4:156:725
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hash matches drivers/base/power/resume.c:28
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hash matches device 0000:01:00.0
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which means that the last trace event was just before trying to resume
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device 0000:01:00.0. Then figure out what driver is controlling that
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device (lspci and /sys/devices/pci* is your friend), and see if you can
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fix it, disable it, or trace into its resume function.
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If no device matches the hash (or any matches appear to be false positives),
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the culprit may be a device from a loadable kernel module that is not loaded
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until after the hash is checked. You can check the hash against the current
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devices again after more modules are loaded using sysfs:
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cat /sys/power/pm_trace_dev_match
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For example, the above happens to be the VGA device on my EVO, which I
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used to run with "radeonfb" (it's an ATI Radeon mobility). It turns out
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that "radeonfb" simply cannot resume that device - it tries to set the
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PLL's, and it just _hangs_. Using the regular VGA console and letting X
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resume it instead works fine.
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NOTE
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====
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pm_trace uses the system's Real Time Clock (RTC) to save the magic number.
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Reason for this is that the RTC is the only reliably available piece of
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hardware during resume operations where a value can be set that will
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survive a reboot.
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Consequence is that after a resume (even if it is successful) your system
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clock will have a value corresponding to the magic number instead of the
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correct date/time! It is therefore advisable to use a program like ntp-date
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or rdate to reset the correct date/time from an external time source when
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using this trace option.
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As the clock keeps ticking it is also essential that the reboot is done
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quickly after the resume failure. The trace option does not use the seconds
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or the low order bits of the minutes of the RTC, but a too long delay will
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corrupt the magic value.
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