Claude review: rust: drm: gem: Introduce shmem::Object::sg_table()

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

Patch Review

**Status: Looks good**

This patch adds the test for the wrong-device rejection path that was introduced in patch 3. The test is well-structured:

```rust
fn fail_sg_table_on_wrong_dev() -> Result {
    let (_dev, drm) = create_drm_dev()?;
    let wrong_dev = faux::Registration::new(c"EvilKunit", None)?;

    let obj = Object::<KunitObject>::new(&drm, PAGE_SIZE, ObjectConfig::default(), ())?;

    assert_eq!(obj.sg_table(wrong_dev.as_ref()).err().unwrap(), EINVAL);

    // If sgt_res was not initialized mistakenly with the wrong device, this should still fail.
    assert_eq!(obj.sg_table(wrong_dev.as_ref()).err().unwrap(), EINVAL);
```

The double-call test is a good edge case check — it verifies that `sgt_res` (the `LazyInit`) isn't accidentally initialized with the wrong device on the first call.

The TODO comments about needing dummy dma_ops for success-path testing are reasonable.

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**Summary**: The series is well-designed and mostly correct. The two actionable items are: (1) fix the kdoc function name in patch 5 to say `__drm_gem_shmem_free_sgt_locked`, and (2) consider adding a NULL guard or `drm_WARN_ON` for `shmem->sgt` in `__drm_gem_shmem_free_sgt_locked()` since it's an exported symbol. The kdoc claim about "unpin" is also inaccurate and should say "DMA unmap and release" instead.

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