On Mon, 1 Mar 2010 12:29:51 +0100
Arnd Bergmann <arnd@xxxxxxxx> wrote:
> On Monday 01 March 2010, FUJITA Tomonori wrote:
> > On Fri, 26 Feb 2010 04:35:36 -0800 (PST)
> > David Miller <davem@xxxxxxxxxxxxx> 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.
Yeah, but the following assumption are not true for sparc, parisc, and
even x86_32 so this ccp trick is not so useful:
/*
* Normally, you have an iommu on 64 bit machines, but not on 32 bit
* machines. Architectures that are differnt should override this.
*/
> > 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.
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
};
/*
@@ -22,17 +24,11 @@ struct scatterlist {
* is 0.
*/
#define sg_dma_address(sg) ((sg)->dma_address)
-#ifndef sg_dma_len
-/*
- * Normally, you have an iommu on 64 bit machines, but not on 32 bit
- * machines. Architectures that are differnt should override this.
- */
-#if __BITS_PER_LONG == 64
+#ifdef CONFIG_NEED_SG_DMA_LENGTH
#define sg_dma_len(sg) ((sg)->dma_length)
#else
#define sg_dma_len(sg) ((sg)->length)
-#endif /* 64 bit */
-#endif /* sg_dma_len */
+#endif
#ifndef ISA_DMA_THRESHOLD
#define ISA_DMA_THRESHOLD (~0UL)
--
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