linux-kernel - Re: [PATCH 02/20] ata_piix: unify code for programming PIO and MWDMA timings

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Date:	Sun, 20 Feb 2011 23:42:48 +0300
From:	Sergei Shtylyov <sshtylyov@...sta.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Sergei Shtylyov <sshtylyov@...sta.com>,
	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/20] ata_piix: unify code for programming PIO and MWDMA
 timings

Hello.

On 20-02-2011 21:59, Alan Cox wrote:

>>> +	if (ata_pio_need_iordy(adev) || use_mwdma)
>>>    		control |= 2;	/* IE enable */

>>      Why IORDY is enabled for MWDMA has always been beyond me... I understand
>> that the stupid Intel docs are to be blamed here.

> I fail to see whats stupid about the docs ?

    Association of IORDY with DMA mode is wrong.

> The same timing register set is used for MWDMA and PIO cycles in MWDMA
> tuned modes (eg ATAPI). Thus the controller needs to be in an MWDMA mode
> whose timings are compatible with the PIO timing and we want IORDY in use
> for the PIO transfer parts.

    Yeah, especially if we also set the bit which only enables fast timing for 
DMA. ;-)
    PIO mode is setup by different code, and it takes care of the IORDY 
setting according to the PIO rules (and it gets called). DMA mode setup should 
just ignore the IORDY setting as in all other sane drivers.

> Alan

WBR, Sergei
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