From mboxrd@z Thu Jan  1 00:00:00 1970
From: Claude Code Review Bot <claude-review@example.com>
To: dri-devel-reviews@example.com
Subject: Claude review: drm/amd/display: use GAMCOR for degamma private props in subsampled format
Date: Thu, 07 May 2026 13:11:56 +1000
Message-ID: <review-patch1-20260506191606.15022-2-mwen@igalia.com>
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References: <20260506191606.15022-1-mwen@igalia.com> <20260506191606.15022-2-mwen@igalia.com>
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Patch Review

**Purpose**: When using subsampled video formats (4:2:0/4:2:2), the PRE_DEG=
AM hardware block (ROM curves) cannot be used because it would affect scale=
r linearity. This patch detects subsampled formats and passes that flag to =
`mod_color_calculate_degamma_params` so it computes distributed points for =
GAMCOR (RAM) instead.

**Correctness of the `map_user_ramp` repurposing**: Passing `is_subsampled_=
format` as the `map_user_ramp` parameter is semantically imprecise but func=
tionally correct. When `true`, it prevents early returns at `color_gamma.c:=
1693-1696` that would keep `TF_TYPE_PREDEFINED`, forcing the function to fa=
ll through to `TF_TYPE_DISTRIBUTED_POINTS` computation. The `ramp=3DNULL` p=
ath is safe =E2=80=94 all ramp accesses are guarded:

```c
// color_gamma.c:1718 =E2=80=94 guards ramp dereference
if (map_user_ramp && ramp && ramp->type =3D=3D GAMMA_RGB_256) {
```

```c
// color_gamma.c:1803 =E2=80=94 same pattern
map_user_ramp && ramp && ramp->type =3D=3D GAMMA_RGB_256,
```

**Whitespace issue**: Line 1457 of `amdgpu_dm_color.c` uses a tab + 7 space=
s for the comment indentation, while surrounding code uses double-tabs. Thi=
s is visible in the applied source:

```c
       } else {
	       /* Check if format requires ... */  =E2=86=90 tab + 7 spaces
		is_subsampled_format =3D ...             =E2=86=90 two tabs
```

The `} else {` at line 1456 also has space-based indentation, but that's a =
pre-existing issue.

**Error logging**: Adding `drm_err()` before returning `-ENOMEM` is a good =
improvement over the silent return in the original code.

**Nit**: The `is_subsampled_format` variable is declared at function scope =
but only used in the `else` branch. Declaring it inside the `else` block wo=
uld be cleaner and make the scope explicit.

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