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

[Christoph Hellwig]

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.