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

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Date:	Mon, 4 Aug 2008 22:06:19 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Robert Hancock <hancockr@...w.ca>
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

> I guess that bit doesn't really make any difference with remotely modern 
> drives, then.. Could we make that ata_id_has_dword_io check always 
> return true if ata_id_is_ata returns true and only check word 48 if not?

I suspect (but need to dig further) that ata_id_has_dword_io should only
be called by pata_legacy.

> I saw Willy Tarreau's patch from February for this, I agree that we 
> should likely use a separate data_xfer method for 32-bit transfer (or if 
> enough controllers should support 32-bit, then just make it be the 
> default and make a separate 16-bit only function for those that don't), 
> rather than punting the decision to the user with hdparm.

Definitely.

> 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
- 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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