Claude review: drm/blend: size zpos array to active planes instead of total

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

Patch Review

**Correctness:** The change is correct. Walking the function at `drm_blend.c:463-511`:

- `total_planes = hweight32(crtc_state->plane_mask)` — counts exactly the bits set in the mask.
- `kmalloc_objs(*states, total_planes)` at line 477 — allocates that many entries.
- `drm_for_each_plane_mask(plane, dev, crtc_state->plane_mask)` at line 485 — iterates exactly over those same bits.
- `states[n++] = plane_state` at line 492 — `n` will reach exactly `total_planes` (assuming no early error exit), so no overrun.

The zero-planes edge case (`plane_mask == 0`) is also fine: `kmalloc_array(0, ...)` returns `ZERO_SIZE_PTR` (non-NULL), the loop body never executes, `sort` and the for-loop with `n=0` are no-ops, and `kfree(ZERO_SIZE_PTR)` is valid.

**Suggested improvement:** Consider using `hweight_long()` or a type-matched weight function instead of `hweight32()` to avoid a silent truncation bug if `plane_mask` is ever widened beyond `u32`:

```c
-	int total_planes = hweight32(crtc_state->plane_mask);
+	int total_planes = hweight_long(crtc_state->plane_mask);
```

Or alternatively, add a static assertion:

```c
BUILD_BUG_ON(sizeof(crtc_state->plane_mask) != sizeof(u32));
```

**Commit message:** The commit message is well written and clearly explains both the problem and the solution. The claim about "reducing memory pressure" is a bit strong for what amounts to saving a few pointers per atomic commit — "tightens the allocation" or "avoids over-allocation" would be more proportionate.

**Verdict:** Correct, low-risk change. Worth applying, ideally with `hweight_long()` for future-proofing.

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Generated by Claude Code Patch Reviewer