linux-kernel - Re: [PATCH 8/15] ide: disable DMA in ->ide_dma

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Date:	Thu, 25 Jan 2007 20:03:17 +0300
From:	Sergei Shtylyov <sshtylyov@...mvista.com>
To:	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
Cc:	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 8/15] ide: disable DMA in ->ide_dma_check for "no IORDY"
 case

Hello.

Bartlomiej Zolnierkiewicz wrote:

>>>The other advantage of doing cleanups is that code becomes cleaner/simpler
>>>which matters a lot for this codebase, i.e. ide-dma-off-void.patch exposed
>>>(yet to be fixed) bug in set_using_dma() (->ide_dma_off_quietly always returns
>>>0 which is passed by ->ide_dma_check to set_using_dma() which incorrectly
>>>then calls ->ide_dma_on).

>>   Well, this seems a newly intruduced bug.

> The old code is so convulted that it is hard to see it w/o cleanup. :)

> ->ide_dma_check implementations often do

> 		return hwif->ide_dma_off_quietly(drive);

> so the return value of ide_dma_off_quietly() (which is always 0) is passed to

> 			if (HWIF(drive)->ide_dma_check(drive)) return -EIO;

> in ide.c:set_using_dma() -> as a result the next line is executed

> 			if (HWIF(drive)->ide_dma_on(drive)) return -EIO;

    So, the error seems to call hwif->ide_dma_on() after hwif->ide_dma_check() 
since hwif->ide_dma_check() must've already called that.

MBR, Sergei
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