linux-kernel - Re: [PATCH] sparc: use asm-generic/scatterlist.h

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Date:	Tue, 2 Mar 2010 21:25:29 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	arnd@...db.de
Cc:	fujita.tomonori@....ntt.co.jp, davem@...emloft.net,
	sparclinux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sparc: use asm-generic/scatterlist.h

On Tue, 2 Mar 2010 13:03:25 +0100
Arnd Bergmann <arnd@...db.de> wrote:

> On Tuesday 02 March 2010, FUJITA Tomonori wrote:
> > If we go with such approach, then we could use something like the
> > following. There are only two kinds of scatterlist definitions (use
> > dma_length or not) so we can cover all the architectures.
> > 
> > diff --git a/include/asm-generic/scatterlist.h b/include/asm-generic/scatterlist.h
> > index 8b94544..1bf620d 100644
> > --- a/include/asm-generic/scatterlist.h
> > +++ b/include/asm-generic/scatterlist.h
> > @@ -11,7 +11,9 @@ struct scatterlist {
> >         unsigned int    offset;
> >         unsigned int    length;
> >         dma_addr_t      dma_address;
> > +#ifdef CONFIG_NEED_SG_DMA_LENGTH
> >         unsigned int    dma_length;
> > +#endif
> >  };
> 
> Yes, that sounds good. If the only reason to need dma_length is virtual merging,
> a clearer (from the Kconfig perspective, not from the implementation) name 
> might be CONFIG_HAVE_IOMMU_VMERGE, similar to the CONFIG_IOMMU_VMERGE option
> on PPC64 that determines the default for the virtual merging runtime option.

Yeah, but IIRC, Alpha, x86_64 GART, parisc, and IA64 don't have
CONFIG_ option for IOMMU virtual merging. I prefer to avoid to adding
something like CONFIG_HAVE_IOMMU_VMERGE for them. If we add
CONFIG_HAVE_IOMMU_VMERGE to them, it's a bit strange not to add the
feature to disable virtual merging for them (I guess GART already has
the feature though).

Actually, I want to use dma_length on all the architectures (if nobody
complains).
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