linux-kernel - Re: Power Management with rootfs on SDMMC.

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Message-ID: <20090102172407.GD1555@ucw.cz>
Date:	Fri, 2 Jan 2009 18:24:13 +0100
From:	Pavel Machek <pavel@...e.cz>
To:	Andreas Mohr <andi@...as.de>
Cc:	Sriram V <vshrirama@...il.com>,
	Pierre Ossman <drzeus-list@...eus.cx>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: Power Management with rootfs on SDMMC.

Hi!

> >   I am using linux-2.6.27.  I am testing power management after
> > booting out of a SD/MMC card.
> >   My root file system is on a SD card.
> > 
> >   I am issuing the following command to suspend
> > 
> >       $ echo -n mem > /sys/power/state
> >  What happens is, The kernel hangs and it does not come out of suspend.
> >  even after i press keypad/generate serial input data.
> 
> 
> > Has anyone tried this before?
> > 
> > Am i missing something here?
> 
> I don't think you're missing much, and you're definitely not alone.
> 
> There have been long threads on mobile phone and netbook related forums about issues
> with seemingly "any slightly advanced use whatsoever" of partitions on SD cards.
> 
> IMHO in this strongly increasingly netbook- and mobile phone-enabled world it's
> a bloody shame that:
...
> - installing a swap partition on an SD card and then resuming can easily
>   go as far as __even completely corrupting__ the entire SD card partitioning
>   plus first partition (corrupts first 1kB of the card: both table and partition)
>   People then immediately resort to a non-helpful "Don't Do This, Ever" reply
>   (using swap partition on SD and suspend, see http://dev.laptop.org/ticket/6532#comment:10),
>   but to this I'd say:
>   News Flash, if this can theoretically be made to work at all using software
>   (i.e. there are no VM-related _hard_ blockers to such an operation
>   of using swap itself on a non-fixed SD slot), then this should goddamn be made
>   to work practically on Linux, _somehow_, since on SSD netbooks this is
>   the most natural thing to do to avoid wear of the builtin device.

I'd like to help with this one... can you reproduce this?


> (or, slightly reworded: I think it's high time for some kernel God to buy a measly
> netbook or some such instead of 16-core mainframes to get a feeling for the
> amount of issues that one hits there)

I have one and yes, its full of problems; see my blog post about 'evil
little cards'.

OTOH currently you can't safely use ext3 on flash card, so suspend
problems seem little 'uninteresting' compared to that.
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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