linux-kernel - Re: [PATCH] [OLPC] sdhci: add quirk for the Marvell CaFe's interrupt timeout

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Message-ID: <20080627193001.5925f664@mjolnir.drzeus.cx>
Date:	Fri, 27 Jun 2008 19:30:01 +0200
From:	Pierre Ossman <drzeus@...eus.cx>
To:	Andres Salomon <dilinger@...ued.net>
Cc:	akpm@...ux-foundation.org, drzeus-sdhci@...eus.cx,
	sdhci-devel@...t.drzeus.cx, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [OLPC] sdhci: add quirk for the Marvell CaFe's
 interrupt timeout

On Mon, 23 Jun 2008 10:13:52 -0400
Andres Salomon <dilinger@...ued.net> wrote:

> 
> The CaFe chip has a hardware bug that ends up with us getting a timeout
> value that's too small, causing the following sorts of problems:
> 
> [   60.525138] mmcblk0: error -110 transferring data
> [   60.531477] end_request: I/O error, dev mmcblk0, sector 1484353
> [   60.533371] Buffer I/O error on device mmcblk0p2, logical block 181632
> [   60.533371] lost page write due to I/O error on mmcblk0p2
> 
> Presumably this is an off-by-one error in the hardware.  Incrementing
> the timeout count value that we stuff into the TIMEOUT_CONTROL register
> gets us a value that works.  This bug was originally discovered by
> Pierre Ossman, I believe.
> 
> [thanks to Robert Millan for proving that this was still a problem]
> 
> Signed-off-by: Andres Salomon <dilinger@...ian.org>

Hmm... I'm not entirely sure about the specifics of the workaround
here. It's likely that we'll have an off-by-minus-one in another
controller, and off-by-two in a third.

Perhaps we should just have "broken timeout" and set the timeout to
0xE. It doesn't cause any side-effects except that the user will have
to wait slightly longer for requests to fail if the card has decided to
crap out.

> @@ -479,6 +482,13 @@ static void sdhci_prepare_data(struct sdhci_host *host, struct mmc_data *data)
>  			break;
>  	}
>  
> +	/*
> +	 * Compensate for an off-by-one error in the CaFe hardware; otherwise,
> +	 * a too-small count gives us interrupt timeouts.
> +	 */

Same issue with "CaFE" as the previous patch.

-- 
     -- Pierre Ossman

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