Re: [PATCH 1/7] arm-nommu: remove the partial DMA_ATTR_NON_CONSISTENT support

[Christoph Hellwig]

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.