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SubjectRe: [PATCH 1/7] arm-nommu: remove the partial DMA_ATTR_NON_CONSISTENT support
On Mon, Jun 24, 2019 at 03:23:08PM +0100, Vladimir Murzin wrote:
> On 6/14/19 3:44 PM, Christoph Hellwig wrote:
> > The arm-nommu DMA code supports DMA_ATTR_NON_CONSISTENT allocations, but
> > does not provide a cache_sync operation. This means any user of it
> > will never be able to actually transfer cache ownership and thus cause
> > coherency bugs.
>
> By the way, Documentation/DMA-attributes.txt doesn't specify cache_sync() as
> requirement for DMA_ATTR_NON_CONSISTENT it only states that it is responsibility
> of the driver to have all the correct and necessary sync points.

True. dma_cache_sync has always been a rather odd interface, as it
doesn't specify in what direction we need to sync and doesn't
participate in our ownership protocol. So my mid-term plan is to kill
it off and replace it with the existing dma_sync_* helpers. This
series is the first step towards that.

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