Dan Malek wrote:
> So, I did a little research. It appears in the case of PowerPC,
> the GFP_DMA can change the way the allocation operates.
> Since the coherent allocator works with pages of memory,
> in the case of a system with highmem, not using GFP_DMA
> could hand you a physical page out of the highmem pool.
I think that's true only if SWIOTLB is enabled. dma_direct_alloc_coherent()
does this:
/* ignore region specifiers */
flag &= ~(__GFP_HIGHMEM);
> This behavior is modified if you specify a restricted DMA
> mask for the device. In this case, dma_alloc_coherent
> will force GFP_DMA on your behalf (on PowerPC).
Isn't it required for all callers of dma_alloc_coherent to specify a mask (via
dma_set_mask) first?
--
Timur Tabi
Linux kernel developer at Freescale
--
Timur Tabi
Linux kernel developer at Freescale
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