[PATCH] drm/ttm: do not try to preserve caching state

[Jerome Glisse]

On Wed, Nov 28, 2012 at 6:13 PM, Jerome Glisse <j.glisse at gmail.com> wrote:
> On Wed, Nov 28, 2012 at 5:18 PM, Thomas Hellstrom <thomas at shipmail.org> wrote:
>> On 11/28/2012 09:09 PM, Jerome Glisse wrote:
>>>
>>> On Wed, Nov 28, 2012 at 10:05 AM,  <j.glisse at gmail.com> wrote:
>>>>
>>>> From: Jerome Glisse <jglisse at redhat.com>
>>>>
>>>> It make no sense to preserve caching state especialy when
>>>> moving from vram to system. It burden the page allocator to
>>>> match the vram caching (often WC) which just burn CPU cycle
>>>> for no good reasons.
>>
>>
>> Nack.
>> This is a driver problem.
>>
>> What happens with this patch if you evict write-combined TT memory to
>> system?
>> That's why we want to preserve caching state in the first place.
>>
>> If you need a different behavior, you can fine-tune in driver::evict_flags,
>> or in the
>> radeon-case in radeon_move_ram_vram / radeon_move_vram_ram.
>
> No you can't. Because cur placement of vram will be wc, and thus it
> will want to preserve it for gtt. Only way to force it is to declare
> vram as cached too.
>
> Cheers,
> Jerome

Now that i think a bit more to it, in all fairness you can do so from
the driver side.

Cheers,
Jerome