[Intel-gfx] [PATCH v2 2/2] drm/i915/color: Downscale degamma lut values read from hardware

[Chaitanya Kumar Borah]

For MTL and beyond, convert back the 24 bit lut values
read from HW to 16 bit values to maintain parity with
userspace values. This way we avoid pipe config mismatch
for pre-csc lut values.

v2: Add helper function to downscale values (Jani)

Signed-off-by: Chaitanya Kumar Borah <chaitanya.kumar.borah at intel.com>
---
 drivers/gpu/drm/i915/display/intel_color.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_color.c b/drivers/gpu/drm/i915/display/intel_color.c
index 15ada7fada96..41666e778c03 100644
--- a/drivers/gpu/drm/i915/display/intel_color.c
+++ b/drivers/gpu/drm/i915/display/intel_color.c
@@ -3456,6 +3456,14 @@ static struct drm_property_blob *glk_read_degamma_lut(struct intel_crtc *crtc)
 	for (i = 0; i < lut_size; i++) {
 		u32 val = intel_de_read_fw(dev_priv, PRE_CSC_GAMC_DATA(pipe));
 
+		/*
+		 * For MTL and beyond, convert back the 24 bit lut values
+		 * read from HW to 16 bit values to maintain parity with
+		 * userspace values
+		 */
+		if (DISPLAY_VER(dev_priv) >= 14)
+			val = change_lut_val_precision(val, 16, 24);
+
 		lut[i].red = val;
 		lut[i].green = val;
 		lut[i].blue = val;
-- 
2.25.1