[Intel-gfx] [PATCH 2/2] drm/i915/color: For MTL convert 24 bit lut values to 16 bit

[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.

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 25c73e2e6fa3..856191640e71 100644
--- a/drivers/gpu/drm/i915/display/intel_color.c
+++ b/drivers/gpu/drm/i915/display/intel_color.c
@@ -3477,6 +3477,14 @@ 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 = mul_u32_u32(val, (1 << 16)) / (1 << 24);
+
 		lut[i].red = val;
 		lut[i].green = val;
 		lut[i].blue = val;
-- 
2.25.1