linux-kernel - Re: PATA DMA problem leading to kernel panic on reading movie DVDs

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Message-ID: <20090519211221.GA6977@wanza.invalid>
Date:	Tue, 19 May 2009 23:12:21 +0200
From:	Martin Lottermoser <Martin.Lottermoser@...nline.de>
To:	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
Cc:	linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org
Subject: Re: PATA DMA problem leading to kernel panic on reading movie DVDs

Hi,

On Tue, May 19, 2009 at 09:30:59PM +0200, Bartlomiej Zolnierkiewicz wrote:
> Incremental patch fixing it:
> 
> diff -u b/drivers/ide/ide-iops.c b/drivers/ide/ide-iops.c
> --- b/drivers/ide/ide-iops.c
> +++ b/drivers/ide/ide-iops.c
> @@ -255,7 +255,7 @@
>  	if (ivb) {
>  		const char *model = (char *)&id[ATA_ID_PROD];
>  
> -		if (strcmp("TSSTcorp CDDVDW SH-S202", model) == 0) {
> +		if (strstr("TSSTcorp CDDVDW SH-S202", model)) {
>  			/*
>  			 * These ATAPI devices always report 80c cable
>  			 * so we have to depend on the host in this case.
> 

I applied that, recompiled, installed, rebooted, and checked the syslog.
The message was still

  hdc: UDMA/66 mode selected

and hdparm also showed "udma4" as being selected. I therefore didn't test
with a DVD.

However, after twice reading the POSIX definition of strstr() I reversed
the order of the arguments to

                if (strstr(model, "TSSTcorp CDDVDW SH-S202")) {

and that did it. Syslog now contained:

  hdc: host side 80-wire cable detection failed, limiting max speed to UDMA33
  hdc: UDMA/33 mode selected

hdparm showed "udma2", and playing movie DVDs worked without DMA being
disabled. :-)

That seems to be it, then. Many thanks for your help, and in particular for
the explanations.

Regards,
Martin Lottermoser
-- 
Martin Lottermoser             Martin.Lottermoser at _REMOVE_t-online.de
Greifswaldstrasse 28
38124 Braunschweig             http://home.vrweb.de/martin.lottermoser
Germany
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