Hi Pekka,
On 10/16/23 14:18, Pekka Paalanen wrote:
On Mon, 16 Oct 2023 12:52:32 +0200
André Almeida <andrealmeid@xxxxxxxxxx> wrote:
Hi Michel,
On 8/17/23 12:37, Michel Dänzer wrote:
On 8/15/23 20:57, André Almeida wrote:
From: Pekka Paalanen <pekka.paalanen@xxxxxxxxxxxxx>
Specify how the atomic state is maintained between userspace and
kernel, plus the special case for async flips.
Signed-off-by: Pekka Paalanen <pekka.paalanen@xxxxxxxxxxxxx>
Signed-off-by: André Almeida <andrealmeid@xxxxxxxxxx>
[...]
+An atomic commit with the flag DRM_MODE_PAGE_FLIP_ASYNC is allowed to
+effectively change only the FB_ID property on any planes. No-operation changes
+are ignored as always. [...]
During the hackfest in Brno, it was mentioned that a commit which re-sets the same FB_ID could actually have an effect with VRR: It could trigger scanout of the next frame before vertical blank has reached its maximum duration. Some kind of mechanism is required for this in order to allow user space to perform low frame rate compensation.
Xaver tested this hypothesis in a flipping the same fb in a VRR monitor
and it worked as expected, so this shouldn't be a concern.
Right, so it must have some effect. It cannot be simply ignored like in
the proposed doc wording. Do we special-case re-setting the same FB_ID
as "not a no-op" or "not ignored" or some other way?
There's an effect in the refresh rate, the image won't change but it
will report that a flip had happened asynchronously so the reported
framerate will be increased. Maybe an additional wording could be like:
Flipping to the same FB_ID will result in a immediate flip as if it was
changing to a different one, with no effect on the image but effecting
the reported frame rate.
Thanks,
pq
