From: Bartlomiej Zolnierkiewicz <bzolnier@elka.pw.edu.pl>
To: Russell King <rmk+lkml@arm.linux.org.uk>
Subject: Re: [patch][9/9] block: remove bio walking
Date: Thu, 9 Sep 2004 16:28:25 +0200
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Cc: linux-ide@vger.kernel.org, linux-kernel@vger.kernel.org,
       Jens Axboe <axboe@suse.de>, Jeff Garzik <jgarzik@pobox.com>
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On Thursday 09 September 2004 16:04, 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.

Yes, it actually works fine. See the other patches from the patchkit. :-)

While at it: AFAICS libata does pci_[un]map_sg() for PIO which is wrong.

> I would rather Jens considered your point first before rewriting code.

OK
 
> 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.)

Could you explain the issue a bit more?
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