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Document pm_tracing actually affecting suspend in non-trivial way. Signed-off-by: Pavel Machek <pavel@ucw.cz> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
86 lines
3.3 KiB
Plaintext
86 lines
3.3 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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pm_trace is not compatible with asynchronous suspend, so it turns
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asynchronous suspend off (which may work around timing or
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ordering-sensitive bugs).
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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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