Re: [PATCH 4/7] dma-direct: provide generic support for uncached kernel segments

[Paul Burton]

Hi Christoph,

On Wed, May 01, 2019 at 07:29:12PM +0200, Christoph Hellwig wrote:
> On Wed, May 01, 2019 at 05:18:59PM +0000, Paul Burton wrote:
> > I'm not so sure about this part though.
> > 
> > On MIPS we currently don't clear the allocated memory with memset. Is
> > doing that really necessary?
> 
> We are clearling it on mips, it is inside dma_direct_alloc_pages.

Ah, of course, I clearly require more caffeine :)

> > If it is necessary then as-is this code will clear the allocated memory
> > using uncached writes which will be pretty slow. It would be much more
> > efficient to perform the memset before arch_dma_prep_coherent() & before
> > converting ret to an uncached address.
> 
> Yes, we could do that.

Great; using cached writes would match the existing MIPS behavior.

Thanks,
    Paul