linux-kernel - Re: Bugs in MMC [was: [Bug 10030] Suspend doesn't work when SD card is inserted]

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Date:	Tue, 4 Mar 2008 14:51:38 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	David Brownell <david-b@...bell.net>
cc:	Pierre Ossman <drzeus-mmc@...eus.cx>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	Zdenek Kabelac <zdenek.kabelac@...il.com>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: Bugs in MMC [was: [Bug 10030] Suspend doesn't work when SD card
 is inserted]

On Tue, 4 Mar 2008, David Brownell wrote:

> > I don't understand this comment.  Suppose a card was inserted while the 
> > system was hibernating.  If the core didn't reprobe, when would that 
> > card be discovered?
> 
> The host controller would tell the core to check for a card, exactly
> like it does at all other times.

But how would the host controller know to do that?  Isn't card 
insertion detection often driven by interrupts?  If a card is 
inserted while the computer is off, no interrupt will be generated.

> That's the natural alternative to having the MMC core assume that card
> detection was broken in low power states, so that the core needed to
> forcibly remove the cards before suspend, and reprobe during resume
> processing.

Is that the assumption the MMC core was really making?  Are you sure it 
wasn't assuming something else (perhaps equally as bad)?

> Having the MMC core make such needless assumptions can cause problems
> for the upper layers, including filesystems.

What's wrong with a superfluous probe at resume time, besides the waste 
of a few milliseconds?

Alan Stern

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