drm/msm: Avoid dirtyfb stalls on video mode displays (v2)

Someone on IRC once asked an innocent enough sounding question:  Why
with xf86-video-modesetting is es2gears limited at 120fps.

So I broke out the perfetto tracing mesa MR and took a look.  It turns
out the problem was drm_atomic_helper_dirtyfb(), which would end up
waiting for vblank.. es2gears would rapidly push two frames to Xorg,
which would blit them to screen and in idle hook (I assume) call the
DIRTYFB ioctl.  Which in turn would do an atomic update to flush the
dirty rects, which would stall until the next vblank.  And then the
whole process would repeat.

But this is a bit silly, we only need dirtyfb for command mode DSI
panels.  So track in plane state whether dirtyfb is required, and
track in the fb how many attached planes require dirtyfb so that we
can skip it when not required.  (Note, mdp4 does not actually have
cmd mode support.)

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20220223191118.881321-1-robdclark@gmail.com
Signed-off-by: Rob Clark <robdclark@chromium.org>

1 files changed, 19 insertions, 1 deletions

diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
index 662b7bc9c219..7763558ef566 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
@@ -1046,6 +1046,20 @@ struct plane_state {
 	u32 pipe_id;
 };
 
+static bool dpu_crtc_needs_dirtyfb(struct drm_crtc_state *cstate)
+{
+	struct drm_crtc *crtc = cstate->crtc;
+	struct drm_encoder *encoder;
+
+	drm_for_each_encoder_mask (encoder, crtc->dev, cstate->encoder_mask) {
+		if (dpu_encoder_get_intf_mode(encoder) == INTF_MODE_CMD) {
+			return true;
+		}
+	}
+
+	return false;
+}
+
 static int dpu_crtc_atomic_check(struct drm_crtc *crtc,
 		struct drm_atomic_state *state)
 {
@@ -1066,6 +1080,7 @@ static int dpu_crtc_atomic_check(struct drm_crtc *crtc,
 	const struct drm_plane_state *pipe_staged[SSPP_MAX];
 	int left_zpos_cnt = 0, right_zpos_cnt = 0;
 	struct drm_rect crtc_rect = { 0 };
+	bool needs_dirtyfb = dpu_crtc_needs_dirtyfb(crtc_state);
 
 	pstates = kzalloc(sizeof(*pstates) * DPU_STAGE_MAX * 4, GFP_KERNEL);
 
@@ -1097,6 +1112,7 @@ static int dpu_crtc_atomic_check(struct drm_crtc *crtc,
 
 	 /* get plane state for all drm planes associated with crtc state */
 	drm_atomic_crtc_state_for_each_plane_state(plane, pstate, crtc_state) {
+		struct dpu_plane_state *dpu_pstate = to_dpu_plane_state(pstate);
 		struct drm_rect dst, clip = crtc_rect;
 
 		if (IS_ERR_OR_NULL(pstate)) {
@@ -1108,11 +1124,13 @@ static int dpu_crtc_atomic_check(struct drm_crtc *crtc,
 		if (cnt >= DPU_STAGE_MAX * 4)
 			continue;
 
-		pstates[cnt].dpu_pstate = to_dpu_plane_state(pstate);
+		pstates[cnt].dpu_pstate = dpu_pstate;
 		pstates[cnt].drm_pstate = pstate;
 		pstates[cnt].stage = pstate->normalized_zpos;
 		pstates[cnt].pipe_id = dpu_plane_pipe(plane);
 
+		dpu_pstate->needs_dirtyfb = needs_dirtyfb;
+
 		if (pipe_staged[pstates[cnt].pipe_id]) {
 			multirect_plane[multirect_count].r0 =
 				pipe_staged[pstates[cnt].pipe_id];