Claude review: drm: writeback: Document behaviour for framebuffer size mismatch

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

Overall Series Review

Subject: drm: writeback: Document behaviour for framebuffer size mismatch
Author: Derek Foreman <derek.foreman@collabora.com>
Patches: 1
Reviewed: 2026-06-04T13:41:03.189082

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This is a single documentation-only patch that adds three lines to the KDoc comment for the `WRITEBACK_FB_ID` property in `drm_writeback.c`. It specifies the expected behavior when the writeback framebuffer dimensions don't match the CRTC dimensions: the driver may either fail the commit or scale the content (but not crop).

The patch is reasonable and addresses a genuine gap in the writeback connector specification. The rationale in the commit message is sound — cropping is underspecified without an origin/viewport property, while scaling is well-defined.

**Minor concerns:**

1. The wording "the driver may either fail or scale (not crop)" is clear but could be slightly more precise about *when* the failure occurs — it should be at atomic check time, not silently at commit time. A `TEST_ONLY` commit should be able to discover this.

2. There's no mention of whether the scaling should preserve aspect ratio or stretch. For a UAPI doc, it might be worth stating this is implementation-defined, or that the framebuffer dimensions define the output size (i.e., stretch to fit).

3. The patch does not add any helper validation or enforcement in the core — it's purely documenting what drivers are allowed to do. That's fine for now, but a follow-up adding a core helper (e.g., a flag on `drm_writeback_connector` indicating scaling support) would make this more useful and consistent across drivers.

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