drm/i915: Fix glk/cnl display w/a #1175

The workaround was supposed to look at the plane destination
coordinates. Currently it's looking at some mixture of src
and dst coordinates that doesn't make sense. Fix it up.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180719182214.4323-2-ville.syrjala@linux.intel.com
Fixes: 394676f0 (drm/i915: Add WA for planes ending close to left screen edge)
Reviewed-by: Imre Deak <imre.deak@intel.com>

drivers/gpu/drm/i915/intel_display.c

@@ -2988,6 +2988,7 @@ static int skl_check_main_surface(const struct intel_crtc_state *crtc_state,
 	int w = drm_rect_width(&plane_state->base.src) >> 16;
 	int h = drm_rect_height(&plane_state->base.src) >> 16;
 	int dst_x = plane_state->base.dst.x1;
+	int dst_w = drm_rect_width(&plane_state->base.dst);
 	int pipe_src_w = crtc_state->pipe_src_w;
 	int max_width = skl_max_plane_width(fb, 0, rotation);
 	int max_height = 4096;
@@ -3009,10 +3010,10 @@ static int skl_check_main_surface(const struct intel_crtc_state *crtc_state,
 	 * screen may cause FIFO underflow and display corruption.
 	 */
 	if ((IS_GEMINILAKE(dev_priv) || IS_CANNONLAKE(dev_priv)) &&
-	    (dst_x + w < 4 || dst_x > pipe_src_w - 4)) {
+	    (dst_x + dst_w < 4 || dst_x > pipe_src_w - 4)) {
 		DRM_DEBUG_KMS("requested plane X %s position %d invalid (valid range %d-%d)\n",
-			      dst_x + w < 4 ? "end" : "start",
-			      dst_x + w < 4 ? dst_x + w : dst_x,
+			      dst_x + dst_w < 4 ? "end" : "start",
+			      dst_x + dst_w < 4 ? dst_x + dst_w : dst_x,
 			      4, pipe_src_w - 4);
 		return -ERANGE;
 	}