drm/amd/display: Use vrr friendly pageflip throttling in DC.

kleinerm · airlied · commit 634092b1b9f6 · 2019-03-05T08:13:39.000+10:00
In VRR mode, keep track of the vblank count of the last completed pageflip in amdgpu_crtc->last_flip_vblank, as recorded in the pageflip completion handler after each completed flip. Use that count to prevent mmio programming a new pageflip within the same vblank in which the last pageflip completed, iow. to throttle pageflips to at most one flip per video frame, while at the same time allowing to request a flip not only before start of vblank, but also anywhere within vblank. The old logic did the same, and made sense for regular fixed refresh rate flipping, but in vrr mode it prevents requesting a flip anywhere inside the possibly huge vblank, thereby reducing framerate in vrr mode instead of improving it, by delaying a slightly delayed flip requests up to a maximum vblank duration + 1 scanout duration. This would limit VRR usefulness to only help applications with a very high GPU demand, which can submit the flip request before start of vblank, but then have to wait long for fences to complete. With this method a flip can be both requested and - after fences have completed - executed, ie. it doesn't matter if the request (amdgpu_dm_do_flip()) gets delayed until deep into the extended vblank due to cpu execution delays. This also allows clients which want to regulate framerate within the vrr range a much more fine-grained control of flip timing, a feature that might be useful for video playback, and is very useful for neuroscience/vision research applications. In regular non-VRR mode, retain the old flip submission behavior. This to keep flip scheduling for fullscreen X11/GLX OpenGL clients intact, if they use the GLX_OML_sync_control extensions glXSwapBufferMscOML(, ..., target_msc,...) function with a specific target_msc target vblank count. glXSwapBuffersMscOML() or DRI3/Present PresentPixmap() will not flip at the proper target_msc for a non-zero target_msc if VRR mode is active with this patch. They'd often flip one frame too early. However, this limitation should not matter much in VRR mode, as scheduling based on vblank counts is pretty futile/unusable under variable refresh duration anyway, so no real extra harm is done. According to some testing already done with this patch by Nicholas on top of my tests, IGT tests didn't report any problems. If fixes stuttering and flickering when flipping at rates below the minimum vrr refresh rate. Fixes: bb47de7 ("drm/amdgpu: Set FreeSync state using drm VRR properties") Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com> Cc: <stable@vger.kernel.org> Cc: Harry Wentland <harry.wentland@amd.com> Cc: Alex Deucher <alexander.deucher@amd.com> Cc: Michel Dänzer <michel@daenzer.net> Tested-by: Bruno Filipe <bmilreu@gmail.com> Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com> Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com> Signed-off-by: Alex Deucher <alexander.deucher@amd.com> Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -4645,6 +4645,8 @@ static void amdgpu_dm_commit_planes(struct drm_atomic_state *state,
 	struct amdgpu_bo *abo;
 	uint64_t tiling_flags, dcc_address;
 	uint32_t target, target_vblank;
+	uint64_t last_flip_vblank;
+	bool vrr_active = acrtc_state->freesync_config.state == VRR_STATE_ACTIVE_VARIABLE;
 
 	struct {
 		struct dc_surface_update surface_updates[MAX_SURFACES];
@@ -4804,7 +4806,31 @@ static void amdgpu_dm_commit_planes(struct drm_atomic_state *state,
 	 * hopefully eliminating dc_*_update structs in their entirety.
 	 */
 	if (flip_count) {
-		target = (uint32_t)drm_crtc_vblank_count(pcrtc) + *wait_for_vblank;
+		if (!vrr_active) {
+			/* Use old throttling in non-vrr fixed refresh rate mode
+			 * to keep flip scheduling based on target vblank counts
+			 * working in a backwards compatible way, e.g., for
+			 * clients using the GLX_OML_sync_control extension or
+			 * DRI3/Present extension with defined target_msc.
+			 */
+			last_flip_vblank = drm_crtc_vblank_count(pcrtc);
+		}
+		else {
+			/* For variable refresh rate mode only:
+			 * Get vblank of last completed flip to avoid > 1 vrr
+			 * flips per video frame by use of throttling, but allow
+			 * flip programming anywhere in the possibly large
+			 * variable vrr vblank interval for fine-grained flip
+			 * timing control and more opportunity to avoid stutter
+			 * on late submission of flips.
+			 */
+			spin_lock_irqsave(&pcrtc->dev->event_lock, flags);
+			last_flip_vblank = acrtc_attach->last_flip_vblank;
+			spin_unlock_irqrestore(&pcrtc->dev->event_lock, flags);
+		}
+
+		target = (uint32_t)last_flip_vblank + *wait_for_vblank;
+
 		/* Prepare wait for target vblank early - before the fence-waits */
 		target_vblank = target - (uint32_t)drm_crtc_vblank_count(pcrtc) +
 				amdgpu_get_vblank_counter_kms(pcrtc->dev, acrtc_attach->crtc_id);
