[PATCH] drm/amdgpu/virtual_dce: Need to pin the fb's bo

[Michel Dänzer]

On 2018-12-21 10:32 a.m., Deng, Emily wrote:
>> -----Original Message-----
>> From: Michel Dänzer <michel at daenzer.net>
>> Sent: Friday, December 21, 2018 5:28 PM
>> To: Deng, Emily <Emily.Deng at amd.com>
>> Cc: amd-gfx at lists.freedesktop.org
>> Subject: Re: [PATCH] drm/amdgpu/virtual_dce: Need to pin the fb's bo
>>
>> On 2018-12-21 10:17 a.m., Deng, Emily wrote:
>>>> From: amd-gfx <amd-gfx-bounces at lists.freedesktop.org> On Behalf Of
>>>> Deng, Emily
>>>>> From: Michel Dänzer <michel at daenzer.net> On 2018-12-21 9:45 a.m.,
>>>>> Deng, Emily wrote:
>>>>>>> From: Michel Dänzer <michel at daenzer.net> On 2018-12-21 8:26 a.m.,
>>>>>>> Emily Deng wrote:
>>>>>>>> When the bo is used to set mode, the bo need to be pinned.
>>>>>>>
>>>>>>> On second thought, why does the BO need to be pinned? When using
>>>>>>> the display hardware, the BO needs to be pinned to prevent it from
>>>>>>> being moved while the hardware is scanning out from it, but that
>>>>>>> shouldn't be
>>>>> necessary here.
>>>>>> The pin here is used for scan out the buffer by remote display app.
>>>>>
>>>>> I still don't understand why pinning is needed. What mechanism does
>>>>> the remote display app use to access the BO contents?
>>>> Sorry, I am not familiar with the remote display app. Maybe it will
>>>> use drm ioctl function to get the current crtc's fb's information,
>>>> and get the content in the fb's buffer object by mmap or translate
>>>> the bo to an OpenGL texture for next rendering. Maybe don't need to
>>>> pin the bo here, as the use has no different with other normal bos.
>>>> So please ignore the patch, and will send another patch to remove the unpin
>> the fb's bo code.
>>> It seems to be hard to remove all the pin for virtual_dce, as it uses some
>> common code in amdgpu_display.c.
>>
>> Because of amdgpu_display_unpin_work_func? That might be as simple as
>> replacing
>>
>> 	schedule_work(&works->unpin_work);
>>
>> with
>>
>> 	kfree(works->shared);
>> 	kfree(works);
>>
>> in dce_virtual_pageflip.
> But the amdgpu_display_crtc_page_flip_target will pin the new_bo, then
> we don't need to unpin it?

Ah, right, but then dce_virtual_pageflip could just unpin it? Not ideal,
but better than leaving it pinned unnecessarily.


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