drm/i915: Turn off pipe gamma when it's not needed

The pipe internal precision is higher than what we currently program to
the degamma/gamma LUTs. We can get a higher quality image by bypassing
the LUTs when they're not needed. Let's do that.

Each plane has its own control bit for this, so we have to update
all active planes. The way we've done this we don't actually have
to run through the whole .check_plane() thing. And we actually
do the .color_check() after .check_plane() so we couldn't even do
that without shuffling the code around.

Additionally on pre-skl we have to update the primary plane regardless
of whether it's active or not on account of the primary plane gamma
enable bit also affecting the pipe bottom color.

v2: Drop the '.' from patch title (Uma)
    Fix 'primayr' typo (Uma,Matt)
    Rebase
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190207202146.26423-5-ville.syrjala@linux.intel.com

drivers/gpu/drm/i915/intel_color.c

@@ -637,6 +637,51 @@ void intel_color_commit(const struct intel_crtc_state *crtc_state)
 	dev_priv->display.color_commit(crtc_state);
 }
 
+static bool need_plane_update(struct intel_plane *plane,
+			      const struct intel_crtc_state *crtc_state)
+{
+	struct drm_i915_private *dev_priv = to_i915(plane->base.dev);
+
+	/*
+	 * On pre-SKL the pipe gamma enable and pipe csc enable for
+	 * the pipe bottom color are configured via the primary plane.
+	 * We have to reconfigure that even if the plane is inactive.
+	 */
+	return crtc_state->active_planes & BIT(plane->id) ||
+		(INTEL_GEN(dev_priv) < 9 &&
+		 plane->id == PLANE_PRIMARY);
+}
+
+static int
+intel_color_add_affected_planes(struct intel_crtc_state *new_crtc_state)
+{
+	struct intel_crtc *crtc = to_intel_crtc(new_crtc_state->base.crtc);
+	struct drm_i915_private *dev_priv = to_i915(crtc->base.dev);
+	struct intel_atomic_state *state =
+		to_intel_atomic_state(new_crtc_state->base.state);
+	const struct intel_crtc_state *old_crtc_state =
+		intel_atomic_get_old_crtc_state(state, crtc);
+	struct intel_plane *plane;
+
+	if (new_crtc_state->gamma_enable == old_crtc_state->gamma_enable)
+		return 0;
+
+	for_each_intel_plane_on_crtc(&dev_priv->drm, crtc, plane) {
+		struct intel_plane_state *plane_state;
+
+		if (!need_plane_update(plane, new_crtc_state))
+			continue;
+
+		plane_state = intel_atomic_get_plane_state(state, plane);
+		if (IS_ERR(plane_state))
+			return PTR_ERR(plane_state);
+
+		new_crtc_state->update_planes |= BIT(plane->id);
+	}
+
+	return 0;
+}
+
 static int check_lut_size(const struct drm_property_blob *lut, int expected)
 {
 	int len;
@@ -661,20 +706,26 @@ int intel_color_check(struct intel_crtc_state *crtc_state)
 	const struct drm_property_blob *degamma_lut = crtc_state->base.degamma_lut;
 	int gamma_length, degamma_length;
 	u32 gamma_tests, degamma_tests;
+	int ret;
 
 	degamma_length = INTEL_INFO(dev_priv)->color.degamma_lut_size;
 	gamma_length = INTEL_INFO(dev_priv)->color.gamma_lut_size;
 	degamma_tests = INTEL_INFO(dev_priv)->color.degamma_lut_tests;
 	gamma_tests = INTEL_INFO(dev_priv)->color.gamma_lut_tests;
 
-	crtc_state->gamma_enable = true;
+	crtc_state->gamma_enable = gamma_lut || degamma_lut;
 
 	if (INTEL_GEN(dev_priv) >= 9 ||
 	    IS_BROADWELL(dev_priv) || IS_HASWELL(dev_priv))
 		crtc_state->csc_enable = true;
 
+	ret = intel_color_add_affected_planes(crtc_state);
+	if (ret)
+		return ret;
+
 	/* Always allow legacy gamma LUT with no further checking. */
-	if (crtc_state_is_legacy_gamma(crtc_state)) {
+	if (!crtc_state->gamma_enable ||
+	    crtc_state_is_legacy_gamma(crtc_state)) {
 		crtc_state->gamma_mode = GAMMA_MODE_MODE_8BIT;
 		return 0;
 	}