| Message ID | 20171003104311.10058-5-hch@lst.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
From: Christoph Hellwig > Sent: 03 October 2017 11:43 > > ia64 does not implement DMA_ATTR_NON_CONSISTENT allocations, so it doesn't > make any sense to do any work in dma_cache_sync given that it must be a > no-op when dma_alloc_attrs returns coherent memory. > > Signed-off-by: Christoph Hellwig <hch@lst.de> > --- > arch/ia64/include/asm/dma-mapping.h | 5 ----- > 1 file changed, 5 deletions(-) > > diff --git a/arch/ia64/include/asm/dma-mapping.h b/arch/ia64/include/asm/dma-mapping.h > index 3ce5ab4339f3..99dfc1aa9d3c 100644 > --- a/arch/ia64/include/asm/dma-mapping.h > +++ b/arch/ia64/include/asm/dma-mapping.h > @@ -48,11 +48,6 @@ static inline void > dma_cache_sync (struct device *dev, void *vaddr, size_t size, > enum dma_data_direction dir) > { > - /* > - * IA-64 is cache-coherent, so this is mostly a no-op. However, we do need to > - * ensure that dma_cache_sync() enforces order, hence the mb(). > - */ > - mb(); > } Are you sure about this one? It looks as though you are doing a mechanical change for all architectures. Some of them are probably stranger than you realise. Even with cache coherent memory any cpu 'store/write buffer' may not be snooped by dma reads. Something needs to flush the store buffer between the last cpu write to the dma buffer and the write (probably a device register) that tells the device it can read the memory. My guess from the comment is that dma_cache_synch() is expected to include that barrier - and it might not be anywhere else. David -- To unsubscribe from this list: send the line "unsubscribe linux-sh" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Wed, Oct 04, 2017 at 08:59:24AM +0000, David Laight wrote:
> Are you sure about this one?
Yes. And if you are not you haven't read either of the cover letter,
the DMA-API documentation, or the reply from Thomas to your mail
yesterday.
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diff --git a/arch/ia64/include/asm/dma-mapping.h b/arch/ia64/include/asm/dma-mapping.h index 3ce5ab4339f3..99dfc1aa9d3c 100644 --- a/arch/ia64/include/asm/dma-mapping.h +++ b/arch/ia64/include/asm/dma-mapping.h @@ -48,11 +48,6 @@ static inline void dma_cache_sync (struct device *dev, void *vaddr, size_t size, enum dma_data_direction dir) { - /* - * IA-64 is cache-coherent, so this is mostly a no-op. However, we do need to - * ensure that dma_cache_sync() enforces order, hence the mb(). - */ - mb(); } #endif /* _ASM_IA64_DMA_MAPPING_H */
ia64 does not implement DMA_ATTR_NON_CONSISTENT allocations, so it doesn't make any sense to do any work in dma_cache_sync given that it must be a no-op when dma_alloc_attrs returns coherent memory. Signed-off-by: Christoph Hellwig <hch@lst.de> --- arch/ia64/include/asm/dma-mapping.h | 5 ----- 1 file changed, 5 deletions(-)