[PATCH v2 2/2] drm/i915/color: Fix Pre-CSC degamma LUT bounds

[Sean Paul <sean@poorly.run>]

From: Sean Paul <seanpaul@google.com>

Fix a typo in the loop condition in xelpd_program_plane_pre_csc_lut
for Segment 2 degamma programming, changing 'while (i++ > 130)' to
'while (i++ < 130)'. Also clamp Segment 2 to the last user-provided
LUT entry value instead of hardcoding it to 1.0 (1 << 24) to fix
a step discontinuity.

Link: https://lore.kernel.org/intel-gfx/20260521180143.2143262-1-sean@poorly.run/ #v1
Signed-off-by: Sean Paul <seanpaul@google.com>

Changes in v2:
- Split out into separate patches for pre/post csc fixes
- Dropped loop bounds fix in favor of [1]

[1]- https://lore.kernel.org/r/20260519075245.383864-1-pranay.samala@intel.com
---
 drivers/gpu/drm/i915/display/intel_color.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_color.c b/drivers/gpu/drm/i915/display/intel_color.c
index 90d5dc2ef3e4..469011c83f9b 100644
--- a/drivers/gpu/drm/i915/display/intel_color.c
+++ b/drivers/gpu/drm/i915/display/intel_color.c
@@ -3953,6 +3953,7 @@ xelpd_program_plane_pre_csc_lut(struct intel_dsb *dsb,
 	enum plane_id plane = to_intel_plane(state->plane)->id;
 	const struct drm_color_lut32 *pre_csc_lut = plane_state->hw.degamma_lut->data;
 	u32 i, lut_size;
+	u32 lut_val = 1 << 24;
 
 	if (icl_is_hdr_plane(display, plane)) {
 		lut_size = 128;
@@ -3963,7 +3964,7 @@ xelpd_program_plane_pre_csc_lut(struct intel_dsb *dsb,
 
 		if (pre_csc_lut) {
 			for (i = 0; i < lut_size; i++) {
-				u32 lut_val = drm_color_lut32_extract(pre_csc_lut[i].green, 24);
+				lut_val = drm_color_lut32_extract(pre_csc_lut[i].green, 24);
 
 				intel_de_write_dsb(display, dsb,
 						   PLANE_PRE_CSC_GAMC_DATA_ENH(pipe, plane, 0),
@@ -3975,7 +3976,7 @@ xelpd_program_plane_pre_csc_lut(struct intel_dsb *dsb,
 			do {
 				intel_de_write_dsb(display, dsb,
 						   PLANE_PRE_CSC_GAMC_DATA_ENH(pipe, plane, 0),
-						   (1 << 24));
+						   lut_val);
 			} while (i++ > 130);
 		} else {
 			for (i = 0; i < lut_size; i++) {
-- 
Sean Paul, Software Engineer, Google / Chromium OS