linux-kernel - Re: Kernel Summit request for Discussion of future of ATA (libata) and IDE

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Date:	Mon, 04 Aug 2008 15:48:17 -0600
From:	Robert Hancock <hancockr@...w.ca>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	ksummit-2008-discuss@...ts.linux-foundation.org,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-ide <linux-ide@...r.kernel.org>,
	Jeff Garzik <jeff@...zik.org>
Subject: Re: Kernel Summit request for Discussion of future of ATA (libata)
 and IDE

Alan Cox wrote:
>> You mentioned in the thread for Willy's patch that "some
>> controllers have quirky rules for 32bit xfers" - any details anywhere?
> 
> There are two main ones
> 
> - Some controllers only support 32bit I/O for a multiple of 32bit values
> [sometimes 'unless the fifo is disabled']. I'd have to go back over the
> docs but I think the AMD may be one of those

The AMD-766 doc I have says that when the Secondary Posted Write Buffer 
or Primary Posted Write Buffer are enabled, only 32-bit writes are 
allowed to the data port. It doesn't say anything about a restriction 
with the read prefetch buffer though.

I guess it depends if any other controllers could potentially have this 
restriction. I suspect non-multiple-of-32-bit transfers are rare enough 
we could just fall back to 16-bit IO always for them, but maybe not.

> - Some controllers (VLB generally) require a magic sequence before the
> transfer. You'll see that in the pata_legacy bits.
> 
> Alan
> 
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