[PATCH] drm/amdgpu: allow write access to mapped userptrs

[Christian König]

Am 17.03.2016 um 20:18 schrieb Jerome Glisse:
> On Fri, Mar 11, 2016 at 3:29 PM, Christian König
> <deathsimple at vodafone.de> wrote:
>> From: Christian König <christian.koenig at amd.com>
>>
>> With the updated MMU notifier we should also be able to
>> handle the writeback case correctly.
>>
> Out of curiosity what are you refering too ? I do not see anything
> special on amdgpu_mn.c logs and i do not see why you could not use
> then for write before.

We moved the get_user_pages() outside of reserving the BO and tested 
that quite extensively.

And don't ask me why that shouldn't have worked. It was you who gave the 
advise to not allow it.

I think the rational was something like that the writeback code disables 
CPU writes, compute a CRC and start to write the page to disk. When the 
GPU could write to the page in that moment the CRC won't match any more 
and we would get errors reported from the disk driver.

But I think that the MMU notifier should catch that case as well.

Cheers,
Christian.