linux-kernel - Re: [patch 6/7] SDHCI: Check DMA for overruns at end of transfer

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Message-ID: <20081119194127.34204891@mjolnir.drzeus.cx>
Date:	Wed, 19 Nov 2008 19:41:27 +0100
From:	Pierre Ossman <drzeus-mmc@...eus.cx>
To:	Ben Dooks <ben-linux@...ff.org>
Cc:	Ben Dooks <ben-linux@...ff.org>, linux-kernel@...r.kernel.org,
	sdhci-devel@...t.drzeus.cx
Subject: Re: [patch 6/7] SDHCI: Check DMA for overruns at end of transfer

On Sun, 16 Nov 2008 00:05:08 +0000
Ben Dooks <ben-linux@...ff.org> wrote:

> On Fri, Nov 14, 2008 at 11:00:26PM +0100, Pierre Ossman wrote:
> > 
> > I'm sorry, but I don't see how this is anywhere near acceptable. This
> > should be a panic at the very least, and until this can be sorted out
> > and avoided the driver should avoid using DMA on these chips.
> 
> A panic won't help get the debug logs out of the kernel.

Indeed, but it will avoid corrupting the system.

> This only
> turned up whilst debugging the controller, I got the timeout clock
> calculation wrong and thus ended up timing out pretty much all the
> CMD25s and seeing this problem.
> 

Just because you had to provoke it doesn't mean it won't appear under
"normal" circumstances for others.

Until this problem is fully understood I think DMA should be turned off
(or possibly needs to be explicitly forced on using Kconfig or a module
parameter).

Do you have any contacts at Samsung that can help out here?

Rgds
-- 
     -- Pierre Ossman

  Linux kernel, MMC maintainer        http://www.kernel.org
  rdesktop, core developer          http://www.rdesktop.org

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