drm/i915/color: fix broken gamma state-checker during boot

Premature gamma lut prepration and loading which was getting
reflected in first modeset causing different colors on
screen during boot.

Issue: In BIOS, gamma is disabled by default. However, legacy read_luts()
was setting crtc_state->base.gamma_lut and gamma_lut was programmed
with junk values which led to visual artifacts (different
colored screens instead of usual black during boot).

Fix: Calling read_luts() only when gamma is enabled which will happen
after first modeset.

This fix is independent from the revert 1b858874 ("Revert
"drm/i915/color: Extract icl_read_luts()"") and should fix different colors
on screen in legacy platforms too.

v2:
-Added gamma_enable checks inside read_luts() [Ville/Jani N]
-Corrected gamma enable check for CHV [Ville]

v3:
-Added check in ilk_read_luts() [Ville]
-Simplified gamma enable check for CHV [Ville]

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111809
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111885Tested-by: Jani Saarinen <jani.saarinen@intel.com>
Signed-off-by: Swati Sharma <swati2.sharma@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191009065542.27415-2-swati2.sharma@intel.com

drivers/gpu/drm/i915/display/intel_color.c

@@ -1613,6 +1613,9 @@ i9xx_read_lut_8(const struct intel_crtc_state *crtc_state)
 
 static void i9xx_read_luts(struct intel_crtc_state *crtc_state)
 {
+	if (!crtc_state->gamma_enable)
+		return;
+
 	crtc_state->base.gamma_lut = i9xx_read_lut_8(crtc_state);
 }
 
@@ -1659,6 +1662,9 @@ i965_read_lut_10p6(const struct intel_crtc_state *crtc_state)
 
 static void i965_read_luts(struct intel_crtc_state *crtc_state)
 {
+	if (!crtc_state->gamma_enable)
+		return;
+
 	if (crtc_state->gamma_mode == GAMMA_MODE_MODE_8BIT)
 		crtc_state->base.gamma_lut = i9xx_read_lut_8(crtc_state);
 	else
@@ -1701,10 +1707,10 @@ chv_read_cgm_lut(const struct intel_crtc_state *crtc_state)
 
 static void chv_read_luts(struct intel_crtc_state *crtc_state)
 {
-	if (crtc_state->gamma_mode == GAMMA_MODE_MODE_8BIT)
-		crtc_state->base.gamma_lut = i9xx_read_lut_8(crtc_state);
-	else
+	if (crtc_state->cgm_mode & CGM_PIPE_MODE_GAMMA)
 		crtc_state->base.gamma_lut = chv_read_cgm_lut(crtc_state);
+	else
+		i965_read_luts(crtc_state);
 }
 
 static struct drm_property_blob *
@@ -1742,6 +1748,12 @@ ilk_read_lut_10(const struct intel_crtc_state *crtc_state)
 
 static void ilk_read_luts(struct intel_crtc_state *crtc_state)
 {
+	if (!crtc_state->gamma_enable)
+		return;
+
+	if ((crtc_state->csc_mode & CSC_POSITION_BEFORE_GAMMA) == 0)
+		return;
+
 	if (crtc_state->gamma_mode == GAMMA_MODE_MODE_8BIT)
 		crtc_state->base.gamma_lut = i9xx_read_lut_8(crtc_state);
 	else
@@ -1788,6 +1800,9 @@ glk_read_lut_10(const struct intel_crtc_state *crtc_state, u32 prec_index)
 
 static void glk_read_luts(struct intel_crtc_state *crtc_state)
 {
+	if (!crtc_state->gamma_enable)
+		return;
+
 	if (crtc_state->gamma_mode == GAMMA_MODE_MODE_8BIT)
 		crtc_state->base.gamma_lut = i9xx_read_lut_8(crtc_state);
 	else