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: 2026-06-04T12:17:50.607491

---

This is a single documentation-only patch (v2) to the DRM writeback connector subsystem. It adds six lines of kernel-doc commentary to the `WRITEBACK_FB_ID` property documentation in `drm_writeback.c`, specifying what should happen when the writeback framebuffer dimensions differ from the attached CRTC dimensions.

The patch is well-motivated: the existing documentation left this behavior entirely undefined, which is a problem for both driver implementers and userspace (compositors like Weston). The chosen policy — allow scaling, forbid cropping, and require failure over partial fills — is reasonable and pragmatic:

- **Scaling** is the natural operation for hardware with scaler blocks in the writeback path.
- **Cropping** is correctly excluded since there's no property to specify a crop origin.
- **Failure over partial fill** is the safe default, preventing garbage data in the output buffer.

The v2 change (making it explicit that partial fills must not occur) is a good improvement.

No functional code changes, no risk of regressions. This is straightforward UAPI documentation clarification.

**Verdict: Looks good.** Minor wording nit below, but nothing blocking.

---
Generated by Claude Code Patch Reviewer