Claude review: drm/panthor: Part ways with drm_gem_shmem_object

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

Patch Review

This is the largest and most impactful patch. It replaces the `drm_gem_shmem_object` base with a plain `drm_gem_object` and implements custom page management, vmap, sgt, pin/unpin, and mmap handling.

Key observations:

1. **`panthor_gem_backing_pin_locked` / `panthor_gem_backing_unpin_locked`**: The pin/unpin pair is clean, with the unpin explicitly leaving pages allocated (lazy cleanup). This is appropriate for the upcoming shrinker.

2. **`panthor_gem_vmap_get_locked` error path**: The error path calls `panthor_gem_backing_unpin_locked(bo)` which is correct — it undoes the pin acquired earlier in the function.

3. **`panthor_gem_free_object`**: For non-imported objects, the cleanup properly takes the resv lock before cleaning up vmap, sgt, and pages. For imported objects, `drm_prime_gem_destroy()` is called. Note that the `MODULE_IMPORT_NS("DMA_BUF")` addition is needed because `drm_prime_gem_destroy` is in that namespace.

4. **Missing `drm_gem_free_mmap_offset`**: The old code called `drm_gem_free_mmap_offset()` but the new code doesn't seem to. However, `drm_gem_object_release()` should handle this via the VMA offset manager cleanup, so this should be fine.

5. **`panthor_gem_create` GFP flags**: The comment about MOVABLE zone and CMA is carried over from shmem. The `GFP_HIGHUSER | __GFP_RETRY_MAYFAIL | __GFP_NOWARN` mask is appropriate.

6. **`panthor_gem_alloc_object` missing `flags` parameter type**: The function takes `uint32_t flags` but the kernel convention is `u32`. Minor style nit.

7. **`to_panthor_bo` change to `container_of_const`**: Good — this properly handles const propagation.

8. The `panthor_gem_fault` handler holds `dma_resv_lock()` unconditionally (non-interruptible) in the fault path. This is a concern — if the lock is contended, userspace can't be interrupted. This is addressed in patch 6 (lazy allocation) where it's reworked.

No blocking issues. The lack of R-b on this patch is notable given its size.

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Generated by Claude Code Patch Reviewer