Re: [PATCH 5/7] MIPS: use the generic uncached segment support in dma-direct

[Paul Burton]

Hi Christoph,

On Tue, Apr 30, 2019 at 10:29:47PM +0200, Christoph Hellwig wrote:
> On Tue, Apr 30, 2019 at 08:10:43PM +0000, Paul Burton wrote:
> > This series looks like a nice cleanup to me - the one thing that puzzles
> > me is the !PageHighMem check above.
> > 
> > As far as I can see arch_dma_prep_coherent() should never be called with
> > a highmem page, so would it make more sense to either drop this check or
> > perhaps wrap it in a WARN_ON()?
> 
> dma_alloc_from_contigous can return highmem pages depending on where
> the CMA area is located.  But given that these pages don't have a
> direct kernel mapping we also shouldn't have to flush the caches
> for them.

Right but dma_direct_alloc_pages() already checks for the PageHighMem
case & returns before ever calling arch_dma_prep_coherent(), no?

Thanks,
    Paul