linux-kernel - Re: [patch] suspend/resume debugging: device filter

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Message-ID: <20070125113233.GC23343@elf.ucw.cz>
Date:	Thu, 25 Jan 2007 12:32:33 +0100
From:	Pavel Machek <pavel@....cz>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...l.org>, Greg KH <gregkh@...e.de>
Subject: Re: [patch] suspend/resume debugging: device filter

Hi!

> Subject: [patch] suspend/resume debugging: device filter
> From: Ingo Molnar <mingo@...e.hu>
> 
> this patch implements the /sys/power/filter attribute, which takes a 
> string. If a device's name matches the filter string (exactly), then 
> that device is excluded from suspend/resume.
> 
> this can be helpful in a number of ways when debugging suspend and 
> resume problems:
> 
>  - if CONFIG_DISABLE_CONSOLE_SUSPEND is used then the serial
>    console is still suspended after which point there's no
>    log output. Doing "echo serial > /sys/power/filter" keeps
>    the serial port active, so any messages (and crash info)
>    after that point is displayed.
> 
>  - if a device is suspected to be the reason of resume failure
>    then it can be excluded via the filter. That device obviously
>    wont work, but users can thus help us debug resume problems
>    in combination with pm_trace, without having to hack the kernel.
> 
> (note that you can obvious break suspend/resume via the filter, by 
> excluding a vital device - so it is only to be used when suspend or 
> resume is broken to begin with.)

Should this go to Documentation/power?

> it might be better to do this centrally in sysfs, via a per-device 
> attribute, to individually enable suspend and resume on a per device 
> basis, but my sysfs-fu is not strong enough for that now ;-)

Yep, I think it should go to per-device attribute. Also it would be
nice to name it somehow like debug_suspend_filter or something, so
that people have less tendency to play with it.
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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