drm/i915: Fix scaling check for 90/270 degree plane rotation

Starting from commit b63a16f6 ("drm/i915: Compute display surface
offset in the plane check hook for SKL+") we've already rotated the src
coordinates by 270 degrees by the time we check if a scaler is needed
or not, so we must not account for the rotation a second time.
Previously we did these steps in the opposite order and hence the
scaler check had to deal with rotation itself. The double rotation
handling causes us to enable a scaler pretty much every time 90/270
degree plane rotation is requested, leading to fuzzier fonts and whatnot.

v2: s/unsigned/unsigned int/ to appease checkpatch
v3: s/DRM_ROTATE_0/DRM_MODE_ROTATE_0/

Cc: stable@vger.kernel.org
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reported-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Tested-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Fixes: b63a16f6 ("drm/i915: Compute display surface offset in the plane check hook for SKL+")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170331180056.14086-2-ville.syrjala@linux.intel.comReviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>

drivers/gpu/drm/i915/intel_display.c

@@ -4610,7 +4610,7 @@ static void cpt_verify_modeset(struct drm_device *dev, int pipe)
 
 static int
 skl_update_scaler(struct intel_crtc_state *crtc_state, bool force_detach,
-		  unsigned scaler_user, int *scaler_id, unsigned int rotation,
+		  unsigned int scaler_user, int *scaler_id,
 		  int src_w, int src_h, int dst_w, int dst_h)
 {
 	struct intel_crtc_scaler_state *scaler_state =
@@ -4619,9 +4619,12 @@ skl_update_scaler(struct intel_crtc_state *crtc_state, bool force_detach,
 		to_intel_crtc(crtc_state->base.crtc);
 	int need_scaling;
 
-	need_scaling = drm_rotation_90_or_270(rotation) ?
-		(src_h != dst_w || src_w != dst_h):
-		(src_w != dst_w || src_h != dst_h);
+	/*
+	 * Src coordinates are already rotated by 270 degrees for
+	 * the 90/270 degree plane rotation cases (to match the
+	 * GTT mapping), hence no need to account for rotation here.
+	 */
+	need_scaling = src_w != dst_w || src_h != dst_h;
 
 	/*
 	 * if plane is being disabled or scaler is no more required or force detach
@@ -4683,7 +4686,7 @@ int skl_update_scaler_crtc(struct intel_crtc_state *state)
 	const struct drm_display_mode *adjusted_mode = &state->base.adjusted_mode;
 
 	return skl_update_scaler(state, !state->base.active, SKL_CRTC_INDEX,
-		&state->scaler_state.scaler_id, DRM_MODE_ROTATE_0,
+		&state->scaler_state.scaler_id,
 		state->pipe_src_w, state->pipe_src_h,
 		adjusted_mode->crtc_hdisplay, adjusted_mode->crtc_vdisplay);
 }
@@ -4712,7 +4715,6 @@ static int skl_update_scaler_plane(struct intel_crtc_state *crtc_state,
 	ret = skl_update_scaler(crtc_state, force_detach,
 				drm_plane_index(&intel_plane->base),
 				&plane_state->scaler_id,
-				plane_state->base.rotation,
 				drm_rect_width(&plane_state->base.src) >> 16,
 				drm_rect_height(&plane_state->base.src) >> 16,
 				drm_rect_width(&plane_state->base.dst),