drm/msm/mdp5: Configure PP_SYNC_HEIGHT to double the vtotal

Leaving this at a close-to-maximum register value 0xFFF0 means it takes
very long for the MDSS to generate a software vsync interrupt when the
hardware TE interrupt doesn't arrive.  Configuring this to double the
vtotal (like some downstream kernels) leads to a frame to take at most
twice before the vsync signal, until hardware TE comes up.

In this case the hardware interrupt responsible for providing this
signal - "disp-te" gpio - is not hooked up to the mdp5 vsync/pp logic at
all.  This solves severe panel update issues observed on at least the
Xperia Loire and Tone series, until said gpio is properly hooked up to
an irq.
Suggested-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@somainline.org>
Signed-off-by: Marijn Suijten <marijn.suijten@somainline.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@somainline.org>
Link: https://lore.kernel.org/r/20210406214726.131534-2-marijn.suijten@somainline.orgSigned-off-by: Rob Clark <robdclark@chromium.org>

drivers/gpu/drm/msm/disp/mdp5/mdp5_cmd_encoder.c

@@ -49,9 +49,17 @@ static int pingpong_tearcheck_setup(struct drm_encoder *encoder,
 		| MDP5_PP_SYNC_CONFIG_VSYNC_IN_EN;
 	cfg |= MDP5_PP_SYNC_CONFIG_VSYNC_COUNT(vclks_line);
 
+	/*
+	 * Tearcheck emits a blanking signal every vclks_line * vtotal * 2 ticks on
+	 * the vsync_clk equating to roughly half the desired panel refresh rate.
+	 * This is only necessary as stability fallback if interrupts from the
+	 * panel arrive too late or not at all, but is currently used by default
+	 * because these panel interrupts are not wired up yet.
+	 */
 	mdp5_write(mdp5_kms, REG_MDP5_PP_SYNC_CONFIG_VSYNC(pp_id), cfg);
 	mdp5_write(mdp5_kms,
-		REG_MDP5_PP_SYNC_CONFIG_HEIGHT(pp_id), 0xfff0);
+		REG_MDP5_PP_SYNC_CONFIG_HEIGHT(pp_id), (2 * mode->vtotal));
+
 	mdp5_write(mdp5_kms,
 		REG_MDP5_PP_VSYNC_INIT_VAL(pp_id), mode->vdisplay);
 	mdp5_write(mdp5_kms, REG_MDP5_PP_RD_PTR_IRQ(pp_id), mode->vdisplay + 1);