Re: How to efficiently handle DMA and cache on ARMv7 ? (was "Isget_user_pages() enough to prevent pages from being swapped out ?")

From: Russell King - ARM Linux
Date: Thu Sep 03 2009 - 04:36:31 EST

On Wed, Sep 02, 2009 at 06:10:44PM +0300, Imre Deak wrote:
> To my understanding buffers returned by dma_alloc_*, kmalloc, vmalloc
> are ok:

For dma_map_*, the only pages/addresses which are valid to pass are
those returned by get_free_pages() or kmalloc. Everything else is
not permitted.

Use of vmalloc'd and dma_alloc_* pages with the dma_map_* APIs is invalid
use of the DMA API. See the notes in the DMA-mapping.txt document
against "dma_map_single".

> For user mappings I think you'd have to do an additional flush for
> the direct mapping, while the user mapping is flushed in dma_map_*.

I will not accept a patch which adds flushing of anything other than
the kernel direct mapping in the dma_map_* functions, so please find
a different approach.
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