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

[Alex Deucher]

On Fri, Dec 21, 2018 at 1:15 PM Christian König
<ckoenig.leichtzumerken at gmail.com> wrote:
>
> Am 21.12.18 um 10:09 schrieb Deng, Emily:
> >> -----Original Message-----
> >> From: Michel Dänzer <michel at daenzer.net>
> >> Sent: Friday, December 21, 2018 4:52 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 9:45 a.m., Deng, Emily wrote:
> >>>> -----Original Message-----
> >>>> From: Michel Dänzer <michel at daenzer.net>
> >>>> Sent: Friday, December 21, 2018 4:38 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 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.
>
> Opening the BO and doing something with it in OpenGL should result in
> proper fencing of the BO, so this sounds like a workaround for a bug
> somewhere else.
>
> As long as this isn't explained further this patch is certainly a NAK.
>
> Pinning for physical displays is allowed because they are limited in
> number, but this is not necessary the case with a virtual output.

Well practically, it's the same as real displays.  We limit the
virtual displays to 6 just like most hw.  It really should overate the
same.  We just don't need the pinning per se because there is no hw
actively scanning out of it.

Alex

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