Re: [patch] PM: suspend/resume debugging should depend on SOFTWARE_SUSPEND

Linus Torvalds
2006-11-19T18:22:09Z

On Sun, 19 Nov 2006, Rafael J. Wysocki wrote:
>
> In fact that's up to 30 seconds on a modern box, usually less than that.

Right. If the machine boots quickly, it's fast. Of course, if the machine
boots quickly, you might as well often just shut down and reboot.

> And suspend-to-ram doesn't work on quilte a lot of boxes right now. Also, you
> can use the software suspend on boxes that don't support the suspend-to-ram
> at all.

One large reason STR often doesn't work is that people don't even test it,
because people point to the suspend-to-disk instead. suspend-to-disk is
the problem, not the solution.

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.

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.

The point being that PM_TRACE is wonderful, and it's wonderful exactly for
NOT using suspend-to-disk. The other point being that people have gotten
lazy, and accept half a minute (minimum - usually it's longer) boot times,
when STR is a lot more pleasant, but it does require some detective work
when it doesn't boot.

I wish more people tried STR, instead of having the STD people tell them
not to!

Linus