Date: Mon, 4 Aug 2008 22:06:19 +0100
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Robert Hancock <hancockr@shaw.ca>
Cc: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>,
       James Bottomley <James.Bottomley@hansenpartnership.com>,
       ksummit-2008-discuss@lists.linux-foundation.org,
       linux-kernel <linux-kernel@vger.kernel.org>,
       linux-ide <linux-ide@vger.kernel.org>, Jeff Garzik <jeff@garzik.org>
Subject: Re: Kernel Summit request for Discussion of future of ATA (libata)
 and IDE
Message-ID: <20080804220619.76b94ceb@lxorguk.ukuu.org.uk>
In-Reply-To: <48977200.3050307@shaw.ca>
References: <fa.OGeO7gZvBG4obEzRbVltjSebgTQ@ifi.uio.no>
	<fa.KtvYE2B2yrJqUleolhtMPN9ljAQ@ifi.uio.no>
	<fa.AqEKTvguYFAzDFHy/We/8MpOqmo@ifi.uio.no>
	<48976168.3020804@shaw.ca>
	<20080804205508.20a3f917@lxorguk.ukuu.org.uk>
	<48977200.3050307@shaw.ca>
Organization: Red Hat UK Cyf., Amberley Place, 107-111 Peascod Street,
 Windsor, Berkshire, SL4 1TE, Y Deyrnas Gyfunol. Cofrestrwyd yng Nghymru a
 Lloegr o'r rhif cofrestru 3798903
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1409
Lines: 32

> 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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/