[PATCH 6/8] drm/amd/display: enable GPU VM support

[Michel Dänzer]

On 27/10/17 04:48 PM, Christian König wrote:
> Am 27.10.2017 um 16:37 schrieb Harry Wentland:
>> On 2017-10-26 12:06 PM, Christian König wrote:
>>> From: Christian König <christian.koenig at amd.com>
>>>
>>> Just set the bit so that DC does the hardware programming.
>>>
>>> Signed-off-by: Christian König <christian.koenig at amd.com>
>>> ---
>>>   drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 2 ++
>>>   1 file changed, 2 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>>> b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>>> index 2188f20..ed4351a 100644
>>> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>>> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
>>> @@ -417,6 +417,8 @@ static int amdgpu_dm_init(struct amdgpu_device
>>> *adev)
>>>         init_data.dce_environment = DCE_ENV_PRODUCTION_DRV;
>>>   +    init_data.flags.gpu_vm_support = true;
>>> +
>> Hi Christian,
>>
>> what ASIC has this been tested on?
> 
> Carizzo.
> 
>> I'm not sure that this won't break dGPU. dGPU doesn't have vm_support
>> but I think DC will still try to write the same registers as for CZ on
>> dGPU if we enable this. We at least need to make sure it doesn't blow up.
> 
> Yeah, as Tom already stumbled over as well it causes a warning on Tonga.
> Currently giving it a spin on Polaris.
> 
>> As for Raven we use this flag on Windows but only tested the case
>> where VM is actually programmed. If VM isn't programmed it might still
>> work but we'd need to give that a spin.
> 
> Without this flag tilling fails and only displays a quite unusual pattern.
> 
> I would actually prefer if we can completely remove this flag and
> instead always enable the VM programming on supported hardware.
> 
> Is there any downside on doing so?

Is there a particular use-case for scanout from system memory with a
dGPU? Otherwise I suspect it's better not to bother, because the failure
mode might be pretty bad if the PCIe link can't keep up with scanout.


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