Claude review: drm/amd/display: use halving distribution for PQ/sRGB linearizing LUT

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

**Purpose**: Replaces the uniform 12-region/16-points-per-region distribution with a 9-region halving distribution for PQ and sRGB EOTFs, concentrating samples in the bright end where these curves are steepest.

**Segment distribution verification**:
```
seg_distr[0] = 0  →  2^0 = 1 point    (region [2^-9, 2^-8])
seg_distr[1] = 0  →  2^0 = 1 point    (region [2^-8, 2^-7])
seg_distr[2] = 1  →  2^1 = 2 points   (region [2^-7, 2^-6])
seg_distr[3] = 2  →  2^2 = 4 points   (region [2^-6, 2^-5])
seg_distr[4] = 3  →  2^3 = 8 points   (region [2^-5, 2^-4])
seg_distr[5] = 4  →  2^4 = 16 points  (region [2^-4, 2^-3])
seg_distr[6] = 5  →  2^5 = 32 points  (region [2^-3, 2^-2])
seg_distr[7] = 6  →  2^6 = 64 points  (region [2^-2, 2^-1])
seg_distr[8] = 7  →  2^7 = 128 points (region [2^-1, 2^0])
Total: 1+1+2+4+8+16+32+64+128 = 256 points ✓
```

This fits within `rgb_resulted[256+3]`. The maximum `seg_distr` value is 7, requiring `increment = 256/128 = 2`, which is within patch 4's capability (up to seg_distr=8).

**Bounds on tf_pts access**: For k=8 (brightest region), `start_index = (-9+8+25)*16 = 384`. Max `i` = `(384<<4) + 256 = 6400`. Max `i >> 4 = 400`, `(i>>4)+1 = 401 < 1025`. Safe.

**Corner point `end_value = 125` for PQ**: With `region_end = 0`, corner_points[1].x = 2^0 = 1.0. The PQ slope computation `(1.0 - Y(1.0)) / (125 - 1.0)` extrapolates from the last sample to the 10000-nit point. This is unchanged from the original function and remains correct.

**Non-PQ/non-sRGB fallback**: Transfer functions other than PQ and sRGB (e.g., GAMMA22, HLG) still use the 12-region uniform distribution. This is a reasonable choice — the halving distribution is specifically tuned for PQ/sRGB curvature.

**Comment style nit**: Lines 352-354 use `//` comments while surrounding comments use `/* */`. This is a minor inconsistency; the kernel accepts both styles but `/* */` is more traditional for multi-word comments in display code.

**Observation on the cover letter's candor**: The author notes no clear visual improvement from patches 4-5. While the mathematical reasoning is sound (more precision where curvature is steepest), the lack of visible improvement suggests the banding was already adequately addressed by patches 1-3's switch to the degamma helper with 192 points. These patches are still worthwhile as future-proofing for higher-precision displays.

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**Summary**: Patches 1-3 are the substantive fix for gradient banding and look correct. Patches 4-5 are a clean precision enhancement. The only actionable item is the whitespace fix in patch 1 (tab+spaces vs double-tab for comment indentation). The series is in good shape overall.

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Generated by Claude Code Patch Reviewer