linux-kernel - Re: [bug] ata subsystem related crash with latest -git

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Message-ID: <20071018171429.GH10674@kernel.dk>
Date:	Thu, 18 Oct 2007 19:14:29 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	fujita.tomonori@....ntt.co.jp, mingo@...e.hu,
	linux-kernel@...r.kernel.org, jgarzik@...ox.com,
	alan@...rguk.ukuu.org.uk, tomof@....org
Subject: Re: [bug] ata subsystem related crash with latest -git

On Thu, Oct 18 2007, Arjan van de Ven wrote:
> On Thu, 18 Oct 2007 09:55:04 -0700 (PDT)
> Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> 
> > 
> > 
> > On Thu, 18 Oct 2007, Jens Axboe wrote:
> > > -		unsigned long addr = page_to_phys(s->page) +
> > > s->offset; 
> > > +		unsigned long addr = page_to_phys(sg_page(s)) +
> > > s->offset; 
> > 
> > Umm. May I suggest (I haven't read the whole thread yet, maybe
> > somebody else already did) that
> > 
> > 	static inline unsigned long sg_phys(struct scatterlist *sg)
> > 	{
> > 		return 	page_to_phys(sg_page(sg)) + sg->offset;
> > 	}
> > 
> > would be a good thing to have?
> > 
> > Very few drivers should care so much about the *page* itself (or the 
> > offset). That's something that the generic allocation code etc cares 
> > about, but the driver is almost bound to care mostly about the actual
> > DMA address
> 
> .... but will that work for systems with IOMMU ? or is it fundamentally
> the wrong interface

They use foo_to_bus() on the address. sg_phys() should of course only be
used where the user previously did page_to_phys() on the sg page.

-- 
Jens Axboe

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