drm: rcar-du: Reject modes that fail CRTC timing requirements

The hardware requires the HDSR and VDSR registers to be set to 1 or
higher. This translates to a minimum combined horizontal sync and back
porch of 20 pixels and a minimum vertical back porch of 3 lines. Reject
modes that fail those requirements.
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>

drivers/gpu/drm/rcar-du/rcar_du_crtc.c

@@ -735,10 +735,22 @@ enum drm_mode_status rcar_du_crtc_mode_valid(struct drm_crtc *crtc,
 	struct rcar_du_crtc *rcrtc = to_rcar_crtc(crtc);
 	struct rcar_du_device *rcdu = rcrtc->group->dev;
 	bool interlaced = mode->flags & DRM_MODE_FLAG_INTERLACE;
+	unsigned int vbp;
 
 	if (interlaced && !rcar_du_has(rcdu, RCAR_DU_FEATURE_INTERLACED))
 		return MODE_NO_INTERLACE;
 
+	/*
+	 * The hardware requires a minimum combined horizontal sync and back
+	 * porch of 20 pixels and a minimum vertical back porch of 3 lines.
+	 */
+	if (mode->htotal - mode->hsync_start < 20)
+		return MODE_HBLANK_NARROW;
+
+	vbp = (mode->vtotal - mode->vsync_end) / (interlaced ? 2 : 1);
+	if (vbp < 3)
+		return MODE_VBLANK_NARROW;
+
 	return MODE_OK;
 }