drm/i915/glk: Fix degamma lut programming

Fixed the glk degamma lut programming which currently
was hard coding a linear lut all the time, making degamma
block of glk basically a pass through.

Currently degamma lut for glk is assigned as 0 in platform
configuration. Updated the same to 33 as per the hardware
capability. IGT tests for degamma were getting skipped due to
this, spotted by Swati.

ToDo: The current gamma/degamm lut ABI has just 16bit for each
color component. This is not enough for GLK+, since input
precision is increased to 3.16 which will need 19bit entries.

v2: Added Matt's RB.

v3: Changed uint32_t to u32.

v4: Fixed Maarten's review comment

Credits-to: Swati Sharma <swati2.sharma@intel.com>
Signed-off-by: Uma Shankar <uma.shankar@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1549893025-21837-2-git-send-email-uma.shankar@intel.com

drivers/gpu/drm/i915/i915_pci.c

@@ -73,7 +73,7 @@
 		   .gamma_lut_tests = DRM_COLOR_LUT_NON_DECREASING, \
 	}
 #define GLK_COLORS \
-	.color = { .degamma_lut_size = 0, .gamma_lut_size = 1024, \
+	.color = { .degamma_lut_size = 33, .gamma_lut_size = 1024, \
 		   .degamma_lut_tests = DRM_COLOR_LUT_NON_DECREASING | \
 					DRM_COLOR_LUT_EQUAL_CHANNELS, \
 	}

drivers/gpu/drm/i915/intel_color.c

@@ -489,6 +489,12 @@ static void bdw_load_gamma_lut(const struct intel_crtc_state *crtc_state, u32 of
 		I915_WRITE(PREC_PAL_GC_MAX(pipe, 1), (1 << 16) - 1);
 		I915_WRITE(PREC_PAL_GC_MAX(pipe, 2), (1 << 16) - 1);
 	}
+
+	/*
+	 * Reset the index, otherwise it prevents the legacy palette to be
+	 * written properly.
+	 */
+	I915_WRITE(PREC_PAL_INDEX(pipe), 0);
 }
 
 /* Loads the palette/gamma unit for the CRTC on Broadwell+. */
@@ -496,7 +502,6 @@ static void broadwell_load_luts(const struct intel_crtc_state *crtc_state)
 {
 	struct intel_crtc *crtc = to_intel_crtc(crtc_state->base.crtc);
 	struct drm_i915_private *dev_priv = to_i915(crtc->base.dev);
-	enum pipe pipe = crtc->pipe;
 
 	if (crtc_state_is_legacy_gamma(crtc_state)) {
 		i9xx_load_luts(crtc_state);
@@ -504,12 +509,6 @@ static void broadwell_load_luts(const struct intel_crtc_state *crtc_state)
 		bdw_load_degamma_lut(crtc_state);
 		bdw_load_gamma_lut(crtc_state,
 				   INTEL_INFO(dev_priv)->color.degamma_lut_size);
-
-		/*
-		 * Reset the index, otherwise it prevents the legacy palette to be
-		 * written properly.
-		 */
-		I915_WRITE(PREC_PAL_INDEX(pipe), 0);
 	}
 }
 
@@ -518,7 +517,7 @@ static void glk_load_degamma_lut(const struct intel_crtc_state *crtc_state)
 	struct intel_crtc *crtc = to_intel_crtc(crtc_state->base.crtc);
 	struct drm_i915_private *dev_priv = to_i915(crtc->base.dev);
 	enum pipe pipe = crtc->pipe;
-	const u32 lut_size = 33;
+	const u32 lut_size = INTEL_INFO(dev_priv)->color.degamma_lut_size;
 	u32 i;
 
 	/*
@@ -529,14 +528,32 @@ static void glk_load_degamma_lut(const struct intel_crtc_state *crtc_state)
 	I915_WRITE(PRE_CSC_GAMC_INDEX(pipe), 0);
 	I915_WRITE(PRE_CSC_GAMC_INDEX(pipe), PRE_CSC_GAMC_AUTO_INCREMENT);
 
-	/*
-	 *  FIXME: The pipe degamma table in geminilake doesn't support
-	 *  different values per channel, so this just loads a linear table.
-	 */
-	for (i = 0; i < lut_size; i++) {
-		u32 v = (i * (1 << 16)) / (lut_size - 1);
+	if (crtc_state->base.degamma_lut) {
+		struct drm_color_lut *lut = crtc_state->base.degamma_lut->data;
+
+		for (i = 0; i < lut_size; i++) {
+			/*
+			 * First 33 entries represent range from 0 to 1.0
+			 * 34th and 35th entry will represent extended range
+			 * inputs 3.0 and 7.0 respectively, currently clamped
+			 * at 1.0. Since the precision is 16bit, the user
+			 * value can be directly filled to register.
+			 * The pipe degamma table in GLK+ onwards doesn't
+			 * support different values per channel, so this just
+			 * programs green value which will be equal to Red and
+			 * Blue into the lut registers.
+			 * ToDo: Extend to max 7.0. Enable 32 bit input value
+			 * as compared to just 16 to achieve this.
+			 */
+			I915_WRITE(PRE_CSC_GAMC_DATA(pipe), lut[i].green);
+		}
+	} else {
+		/* load a linear table. */
+		for (i = 0; i < lut_size; i++) {
+			u32 v = (i * (1 << 16)) / (lut_size - 1);
 
-		I915_WRITE(PRE_CSC_GAMC_DATA(pipe), v);
+			I915_WRITE(PRE_CSC_GAMC_DATA(pipe), v);
+		}
 	}
 
 	/* Clamp values > 1.0. */
@@ -546,23 +563,12 @@ static void glk_load_degamma_lut(const struct intel_crtc_state *crtc_state)
 
 static void glk_load_luts(const struct intel_crtc_state *crtc_state)
 {
-	struct intel_crtc *crtc = to_intel_crtc(crtc_state->base.crtc);
-	struct drm_i915_private *dev_priv = to_i915(crtc->base.dev);
-	enum pipe pipe = crtc->pipe;
-
 	glk_load_degamma_lut(crtc_state);
 
-	if (crtc_state_is_legacy_gamma(crtc_state)) {
+	if (crtc_state_is_legacy_gamma(crtc_state))
 		i9xx_load_luts(crtc_state);
-	} else {
+	else
 		bdw_load_gamma_lut(crtc_state, 0);
-
-		/*
-		 * Reset the index, otherwise it prevents the legacy palette to be
-		 * written properly.
-		 */
-		I915_WRITE(PREC_PAL_INDEX(pipe), 0);
-	}
 }
 
 static void cherryview_load_luts(const struct intel_crtc_state *crtc_state)