Re: [PATCH V2] net: ethernet: mellanox: correct page conversion

[okaya]

On 2016-04-18 00:00, David Miller wrote:
> From: Sinan Kaya <okaya@xxxxxxxxxxxxxx>
> Date: Sat, 16 Apr 2016 18:23:32 -0400
>
> > Current code is assuming that the address returned by 
> > dma_alloc_coherent
> > is a logical address. This is not true on ARM/ARM64 systems. This 
> > patch
> > replaces dma_alloc_coherent with dma_map_page API. The address 
> > returned
> > can later by virtually mapped from the CPU side with vmap API.
> >
> > Signed-off-by: Sinan Kaya <okaya@xxxxxxxxxxxxxx>
>
> You can't do this.
>
> The DMA map page API gives non-coherent mappings, and thus requires
> proper flushing.
>
> So a straight conversion like this is never legitimate.

I would agree on proper dma api usage. However, the code is already 
assuming coherent architecture by mapping the cpu pages as page_kernel.

Dma_map_page returns cached buffers and you don't need cache flushes on 
coherent architecture to make the data visible.