Claude review: drm/hibmc: Use drm_atomic_helper_check_plane_state()

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

Patch Review

**Status: Good**

This correctly replaces the hand-rolled plane validation with the standard `drm_atomic_helper_check_plane_state()` helper. The key changes:

```c
ret = drm_atomic_helper_check_plane_state(new_plane_state, new_crtc_state,
                                          DRM_PLANE_NO_SCALING,
                                          DRM_PLANE_NO_SCALING,
                                          false, true);
```

- `can_position=false` is correct for a primary plane that must fully cover the CRTC.
- `can_update_disabled=true` is the right call -- the original code returned early when `!crtc_state->enable`, but letting the helper still initialize plane state is cleaner and safer.
- The switch from `drm_atomic_get_crtc_state()` to `drm_atomic_get_new_crtc_state()` is a subtle but correct improvement: the old call would add the CRTC to the atomic state (potentially forcing a modeset), while the new call only retrieves it if already present. `drm_atomic_helper_check_plane_state()` handles `new_crtc_state == NULL` correctly by treating the plane as not visible.
- The visibility check (`!new_plane_state->visible`) gates the stride validation below, which is correct since there's no point checking stride on an invisible plane.

The commit message is thorough and the Fixes/Cc:stable tags are appropriate.

---
Generated by Claude Code Patch Reviewer