RE: [PATCH 8/9] dspbridge: add map support for big buffers

[FUJITA Tomonori]

On Thu, 26 Aug 2010 08:16:24 -0500
"Guzman Lugo, Fernando" <fernando.lugo@xxxxxx> wrote:

> >From a quick look, arch/arm/plat-omap/iovmm.c does nothing wrong about
> >scatter gather chaining. arm/arm/mm/dma-mapping.c looks fine too about
> >it. Maybe just defining ARCH_HAS_SG_CHAIN works?
> 
> I can try, but it looks tricky for me. Maybe someone else can tell us why
> SG chain is not supported for ARM or if there is a problem just defining 
> ARCH_HAS_SG_CHAIN.

I suppose that nobody in ARM has been interested in the feature. It
was invented to improve I/O performance with large I/O requests. No
wonder embeded people aren't interested in it.

fujita@rose:~/git/linux-2.6$ find arch -name 'scatterlist.h'|xargs grep HAS_SG
arch/x86/include/asm/scatterlist.h:#define ARCH_HAS_SG_CHAIN
arch/ia64/include/asm/scatterlist.h:#define ARCH_HAS_SG_CHAIN
arch/sparc/include/asm/scatterlist.h:#define ARCH_HAS_SG_CHAIN
arch/powerpc/include/asm/scatterlist.h:#define ARCH_HAS_SG_CHAIN
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