Re: using DMA-API on ARM

Russell King - ARM Linux
2014-12-05T19:25:57Z

On Fri, Dec 05, 2014 at 08:22:05PM +0100, Arend van Spriel wrote:
> On 12/05/14 19:28, Catalin Marinas wrote:
> >This is solved by using a pre-allocated, pre-mapped atomic_pool which
> >avoids any further mapping. __dma_alloc() calls __alloc_from_pool() when
> >!__GFP_WAIT.
>
> So we are actually calling dma_alloc_coherent() with GFP_KERNEL during
> device probe. That last paragraph Russell pointed out seems to suggest this
> is not allowed.

device probe is a schedulable, sleepable context, so dma_alloc_coherent()
is fine there. As Catalin points out, and as I realised after sending
them ail, it does check for __GFP_WAIT and uses a smaller atomic pool
for those allocations. This explains why no one has hit any warnings in
map_vm_area.

So, it's safe from atomic contexts after all.

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