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

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Date:	Mon, 1 Mar 2010 12:29:51 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Cc:	davem@...emloft.net, sparclinux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sparc: use asm-generic/scatterlist.h

On Monday 01 March 2010, FUJITA Tomonori wrote:
> On Fri, 26 Feb 2010 04:35:36 -0800 (PST)
> David Miller <davem@...emloft.net> wrote:
>
> You are referring to the following code (I guess that this hack came
> from x86)?
> 
> #if __BITS_PER_LONG == 64
> #define sg_dma_len(sg)          ((sg)->dma_length)
> #else
> #define sg_dma_len(sg)          ((sg)->length)
> #endif /* 64 bit */
> 
> if so, seems that you are right. we could simply have:
> 
> #define sg_dma_len(sg)          ((sg)->dma_length)

I did it the above way so it would work for any architecture that
wants it. IIRC, similar constructs were used in multiple architectures
before, using the __BITS_PER_LONG macro made this portable.
 
> The current users of asm-generic/scatterlist.h are microblaze, s390,
> score, sh, and x86.
> 
> The first three users don't support DMA so sg_dma_len doesn't matter
> for them.
> 
> sh and x86_32 use sg->length, x86_64 uses sg->dma_length. However, sh
> and x86_32 sets dma_length in dma_map_sg() so they can use
> sg->dma_length.
> 
> I'll clean up this in the next merge window.

Ok, great. I think a good way to clean this up would be to convert
all architectures to use asm-generic/scatterlist.h first, and then
move it to linux/scatterlist once it is architecture intedepent.

	Arnd
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