Re: [RFC PATCH] drm: disable WC optimization for cache coherent devices on non-x86

Michel Dänzer
2019-01-21T17:55:33Z

On 2019-01-21 5:30 p.m., Ard Biesheuvel wrote:
> On Mon, 21 Jan 2019 at 17:22, Christoph Hellwig <hch@infradead.org> wrote:
>
>> Until that happens we should just change the driver ifdefs to default
>> the hacks to off and only enable them on setups where we 100%
>> positively know that they actually work. And document that fact
>> in big fat comments.
>
> Well, as I mentioned in my commit log as well, if we default to off
> unless CONFIG_X86, we may break working setups on MIPS and Power where
> the device is in fact non-cache coherent, and relies on this
> 'optimization' to get things working.

FWIW, the amdgpu driver doesn't rely on non-snooped transfers for
correct basic operation (the scenario Christian brought up is a very
specialized use-case), so that shouldn't be an issue.

--
Earthling Michel Dänzer | http://www.amd.com
Libre software enthusiast | Mesa and X developer