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

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

Patch Review

**Correctness:** The documentation accurately captures a sensible policy. It properly handles the three possible outcomes for size mismatch: scale (allowed), crop (disallowed), fail (always available as fallback). The "must fail instead of partially filling" language is a good addition in v2.

**Wording nit:** The phrase "an odd width for a sub-sampled format" at line 65:
```
+ *	such as hardware scaler constraints or an odd width for a sub-sampled
+ *	format, the writeback must fail instead of partially filling the buffer.
```
This example is reasonable but slightly tangential — odd-width-with-subsampling is more of a general format constraint issue than something specific to the scaling-vs-mismatch scenario being documented. It's fine as-is since it illustrates "unable to exactly fill," but a reviewer could argue it muddies the focus. Not worth blocking on.

**Integration with existing text:** The new text slots in cleanly between the description of what `WRITEBACK_FB_ID` stores and the instruction that "Userspace must set this property to an output buffer every time...". The flow reads naturally.

**Missing consideration:** The patch doesn't mention whether aspect ratio must be preserved during scaling, or whether arbitrary stretching is permitted. This is presumably left to the driver, which seems fine for now — adding aspect ratio constraints could come in a follow-up if needed.

**Reviewed-by: Looks good to merge.**

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Generated by Claude Code Patch Reviewer