Messages in this thread | | | Date | Mon, 19 Nov 2007 16:46:11 -0800 (PST) | Subject | Re: SCSI breakage on non-cache coherent architectures | From | David Miller <> |
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From: Benjamin Herrenschmidt <benh@kernel.crashing.org> Date: Tue, 20 Nov 2007 11:34:24 +1100
> Do you still think we should introduce this __dma_cacheline_aligned ? Do > you see other cases of drivers where it would be useful ? It tend to > agree with your earlier statement that drivers doing that are broken and > should be using a separate allocator for DMA'ble objects (in fact, on > non-cache coherent archs, kmalloc is just fine).
I don't care either way.
If we say that the DMA api works on "DMA cacheline boundaries" (and in reality it does) we do need to either:
1) Require that entire buffers are commited by call sites, and thus "embedding" DMA'd within non-DMA stuff isn't allowed
2) Add the __dma_cacheline_aligned tag.
But note that with #2 it could get quite ugly because the alignment and size both have a minimum that needs to be enforced, not just the alignment alone. So either:
struct foo { unsigned int other_unrelated_stuff;
struct object dma_thing __dma_cacheline_aligned;
unsigned int more_nondma_stuff __dma_cacheline_aligned; };
or:
struct foo { unsigned int other_unrelated_stuff;
union { struct object dma_thing __dma_cacheline_aligned; char __pad[(sizeof(object) + DMA_CACHELINE_SIZE & ~DMA_CACHELINE_SIZE)]; } u;
unsigned int more_nondma_stuff __dma_cacheline_aligned; };
I hope you see what I'm trying to say. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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