| Message ID | 20171003104311.10058-8-hch@lst.de (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
| Series | [01/11] floppy: consolidate the dummy fd_cacheflush definition | expand |
Le 03/10/2017 à 12:43, Christoph Hellwig a écrit : > powerpc 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. What about arch/powerpc/mm/dma-noncoherent.c ? Powerpc 8xx doesn't have coherent memory. Christophe > > Signed-off-by: Christoph Hellwig <hch@lst.de> > --- > arch/powerpc/include/asm/dma-mapping.h | 2 -- > 1 file changed, 2 deletions(-) > > diff --git a/arch/powerpc/include/asm/dma-mapping.h b/arch/powerpc/include/asm/dma-mapping.h > index eaece3d3e225..320846442bfb 100644 > --- a/arch/powerpc/include/asm/dma-mapping.h > +++ b/arch/powerpc/include/asm/dma-mapping.h > @@ -144,8 +144,6 @@ static inline phys_addr_t dma_to_phys(struct device *dev, dma_addr_t daddr) > static inline void dma_cache_sync(struct device *dev, void *vaddr, size_t size, > enum dma_data_direction direction) > { > - BUG_ON(direction == DMA_NONE); > - __dma_sync(vaddr, size, (int)direction); > } > > #endif /* __KERNEL__ */ >
On 03/10/17 12:24, Christophe LEROY wrote: > > > Le 03/10/2017 à 12:43, Christoph Hellwig a écrit : >> powerpc 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. > What about arch/powerpc/mm/dma-noncoherent.c ? AFAICS, just like the ARM code from which it is derived, that will always return a non-cacheable remap of the allocation, which should thus not require explicit maintenance after CPU accesses. dma_cache_sync() would only matter if dma_alloc_attrs(..., DMA_ATTR_NON_CONSISTENT) got special treatment and was allowed to return a cacheable address, but PPC doesn't even propagate the attrs to its internal __dma_alloc_coherent() implementations. Robin. > Powerpc 8xx doesn't have coherent memory. > > Christophe > >> >> Signed-off-by: Christoph Hellwig <hch@lst.de> >> --- >> arch/powerpc/include/asm/dma-mapping.h | 2 -- >> 1 file changed, 2 deletions(-) >> >> diff --git a/arch/powerpc/include/asm/dma-mapping.h >> b/arch/powerpc/include/asm/dma-mapping.h >> index eaece3d3e225..320846442bfb 100644 >> --- a/arch/powerpc/include/asm/dma-mapping.h >> +++ b/arch/powerpc/include/asm/dma-mapping.h >> @@ -144,8 +144,6 @@ static inline phys_addr_t dma_to_phys(struct >> device *dev, dma_addr_t daddr) >> static inline void dma_cache_sync(struct device *dev, void *vaddr, >> size_t size, >> enum dma_data_direction direction) >> { >> - BUG_ON(direction == DMA_NONE); >> - __dma_sync(vaddr, size, (int)direction); >> } >> #endif /* __KERNEL__ */ >>
On Tue, Oct 03, 2017 at 01:24:57PM +0200, Christophe LEROY wrote: >> powerpc 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. > What about arch/powerpc/mm/dma-noncoherent.c ? > > Powerpc 8xx doesn't have coherent memory. It doesn't implement the DMA_ATTR_NON_CONSISTENT interface either, so if it really doesn't have a way to provide dma coherent allocation (although the code in __dma_alloc_coherent suggests it does provide dma coherent allocations) I have no idea how it could ever have worked.
Le 03/10/2017 à 13:43, Christoph Hellwig a écrit : > On Tue, Oct 03, 2017 at 01:24:57PM +0200, Christophe LEROY wrote: >>> powerpc 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. >> What about arch/powerpc/mm/dma-noncoherent.c ? >> >> Powerpc 8xx doesn't have coherent memory. > > It doesn't implement the DMA_ATTR_NON_CONSISTENT interface either, > so if it really doesn't have a way to provide dma coherent allocation > (although the code in __dma_alloc_coherent suggests it does provide > dma coherent allocations) I have no idea how it could ever have > worked. > Yes indeed it provides coherent memory by allocation non cached memory. And drivers aiming at using non coherent memory do it by using kmalloc() with GFP_DMA then dma_map_single(). Then they use dma_sync_single_for_xxx(), which calls __dma_sync() on the 8xx and is a nop on other powerpcs. Christophe
diff --git a/arch/powerpc/include/asm/dma-mapping.h b/arch/powerpc/include/asm/dma-mapping.h index eaece3d3e225..320846442bfb 100644 --- a/arch/powerpc/include/asm/dma-mapping.h +++ b/arch/powerpc/include/asm/dma-mapping.h @@ -144,8 +144,6 @@ static inline phys_addr_t dma_to_phys(struct device *dev, dma_addr_t daddr) static inline void dma_cache_sync(struct device *dev, void *vaddr, size_t size, enum dma_data_direction direction) { - BUG_ON(direction == DMA_NONE); - __dma_sync(vaddr, size, (int)direction); } #endif /* __KERNEL__ */
powerpc 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/powerpc/include/asm/dma-mapping.h | 2 -- 1 file changed, 2 deletions(-)