Subject: Re: SII SATA request size limit
From: Justin Cormack <justin@street-vision.com>
To: Jens Axboe <axboe@suse.de>
Cc: casino_e@terra.es, Kernel mailing list <linux-kernel@vger.kernel.org>
In-Reply-To: <20030915153255.GB3412@suse.de>
References: <d95d2d93f8.d93f8d95d2@teleline.es> 
	<20030915153255.GB3412@suse.de>
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Date: 15 Sep 2003 17:00:54 +0100
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On Mon, 2003-09-15 at 16:32, Jens Axboe wrote:
> On Mon, Sep 15 2003, CASINO_E wrote:
> > Forgive me if I'm saying something stupid but, do you mean a special 
> > case for this controller in ide-dma.c:ide_build_dmatable()?
> 
> No that's not stupid at all. In 2.4 that would be how you do it, in 2.6
> I was referring to the possibility of letting the drive queues that hang
> off that controller be naturally limited. So you would do something ala
> 
> 	if (hwif->dma_boundary)
> 		blk_queue_segment_boundary(drive->queue, 0x1fff);
> 
> and then no segment would be >= 8192 (or cross it, naturally) by
> default.
> 
> > In this case, should not segment size and boundary be included in hwif 
> > so we can have a generic ide_build_dmatable() without dealing 
> > explicitly with special cases? We could initialize to the default for 
> > most controllers and set the values for the exceptions inside each 
> > particular driver.
> 
> Of course. But that is implementation detail, I was just worried that
> someone would clamp on a nasty work around like 15 sectors (which would
> in reality be just a 4kb request, nasty!) when you could get nice 128kb
> requests with just the right segment limiting instead.
> 
> But basically I don't understand why the work-around was _ever_ in
> sectors, if that is the bug in the hardware dma engine. Two
> explanations: it's not really that bug and NetBSD is wrong, or the
> person who did the work-around didn't know a better solution existed
> (don't laugh, I wouldn't be surprised if something like that came down
> from a vendor :)

Unfortunately the bug isnt exactly this (apparently) and is only
revealed under NDA (see Alan Cox's mail).

justin


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