Date: Thu, 9 Sep 2004 16:32:44 +0200
From: Jens Axboe <axboe@suse.de>
To: Bartlomiej Zolnierkiewicz <bzolnier@elka.pw.edu.pl>,
       linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [patch][9/9] block: remove bio walking
Message-ID: <20040909143244.GY1737@suse.de>
References: <200409082127.04331.bzolnier@elka.pw.edu.pl> <20040909090314.A24950@flint.arm.linux.org.uk> <200409091553.13918.bzolnier@elka.pw.edu.pl> <20040909150444.C6434@flint.arm.linux.org.uk>
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On Thu, Sep 09 2004, Russell King wrote:
> On Thu, Sep 09, 2004 at 03:53:13PM +0200, Bartlomiej Zolnierkiewicz wrote:
> > On Thursday 09 September 2004 10:03, Russell King wrote:
> > > On Wed, Sep 08, 2004 at 09:27:04PM +0200, Bartlomiej Zolnierkiewicz wrote:
> > > > [patch] block: remove bio walking
> > > > 
> > > > IDE driver was the only user of bio walking code.
> > 
> > was in -bk10 :-(
> > 
> > > The MMC driver also uses this.  Please don't remove.
> > 
> > OK I'll just drop this patch but can't we also use scatterlists in MMC?
> > 
> > The point is that I now think bio walking was a mistake and accessing
> > bios directly from low-level drivers is a layering violation (thus
> > all the added complexity). Moreover with fixed IDE PIO and without
> > bio walking code it should be possible to shrink struct request by
> > removing all "current" entries.
> 
> I'm wondering whether it is legal to map onto SG lists and then do PIO.
> Provided we don't end up using the DMA API and then using PIO to the
> original pages, it should work.

Will be fine.

> I would rather Jens considered your point first before rewriting code.
> 
> However, using the SG lists does finally provide us with a nice way to
> ensure that we have the right information to finally fix IDE wrt the
> PIO cache issues (dirty cache lines being left in the page cache.)

You can do this directly from the bio. Probably mmc should just do a
make_request_fn hook instead and just fill in a scatter gather table
directly and submit.

-- 
Jens Axboe

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