drm/msm/mdp5: Always generate active-high sync signals for DSI

DSI video mode engine can only take active-high sync signals. This
change prevents MDP5 sending active-low sync signals to DSI in any
case.
Signed-off-by: Hai Li <hali@codeaurora.org>
Tested-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>

drivers/gpu/drm/msm/mdp/mdp5/mdp5_encoder.c

@@ -144,10 +144,14 @@ static void mdp5_encoder_mode_set(struct drm_encoder *encoder,
 			mode->type, mode->flags);
 
 	ctrl_pol = 0;
+
+	/* DSI controller cannot handle active-low sync signals. */
+	if (mdp5_encoder->intf.type != INTF_DSI) {
 		if (mode->flags & DRM_MODE_FLAG_NHSYNC)
 			ctrl_pol |= MDP5_INTF_POLARITY_CTL_HSYNC_LOW;
 		if (mode->flags & DRM_MODE_FLAG_NVSYNC)
 			ctrl_pol |= MDP5_INTF_POLARITY_CTL_VSYNC_LOW;
+	}
 	/* probably need to get DATA_EN polarity from panel.. */
 
 	dtv_hsync_skew = 0;  /* get this from panel? */