Claude review: drm/i915/color: Extract HDR post-CSC LUT programming to helper function

Claude Code Review Bot
2026-04-12T03:07:24Z

Patch Review

**Issue (minor)**: The commit message says "removes the segment 0 index register writes as it is not currently programmed." The old code had:
```c
intel_de_write_dsb(display, dsb, PLANE_POST_CSC_GAMC_SEG0_INDEX_ENH(...),
PLANE_PAL_PREC_AUTO_INCREMENT);
...
intel_de_write_dsb(display, dsb, PLANE_POST_CSC_GAMC_SEG0_INDEX_ENH(...), 0);
```
These are silently removed in the refactoring. While the old code had a `/*TODO: Add for segment 0 */` comment and wasn't programming any actual data to segment 0, removing the index register setup changes behavior. If the hardware requires the segment 0 index to be reset to 0 after programming, this could leave it in an inconsistent state. At minimum, a comment explaining why segment 0 programming is intentionally omitted would help future readers.