Claude review: drm: Remove DRIVER_GEM_GPUVA feature flag

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

Patch Review

**Core DRM changes (drm_gem.c, drm_drv.h, drm_gem.h, drm_debugfs.h):**

These are correct. The key observations:

1. `drm_gem_gpuva_init()` is just `INIT_LIST_HEAD(&obj->gpuva.list)` — calling it unconditionally for every GEM object is harmless. The `mutex_init(&obj->gpuva.lock)` at line 230 of `drm_gem.c` is already unconditional, so the list head init is the only thing that was gated.

2. The `DRM_DEBUGFS_GPUVA_INFO` change from `DRIVER_GEM_GPUVA` to `0` is correct. Looking at `drm_debugfs_create_files()`:
   ```c
   if (features && !drm_core_check_all_features(dev, features))
       continue;
   ```
   Passing `0` means `features` is falsy, so the condition short-circuits and the entry is always created — but only for drivers that actually use `DRM_DEBUGFS_GPUVA_INFO` in their debugfs info list (panthor and nouveau). Non-GPUVA drivers never reference this macro, so they don't get a spurious "gpuvas" debugfs entry. This is fine.

3. Removing the enum value and doc comment from `drm_drv.h` is clean. Note that `BIT(8)` is left as a gap — this is normal for DRM driver feature flags and avoids ABI issues with out-of-tree drivers.

4. The doc update in `drm_gem.h` removing the "only necessary for drivers intending to support DRIVER_GEM_GPUVA" comment is appropriate.

**Driver changes (pvr_drv.c, msm_drv.c, nouveau_drm.c, panthor_drv.c, xe_device.c):**

All driver removals of the flag from `.driver_features` look correct and mechanical.

**One point to note — nouveau double-init:**

In `nouveau_bo.c:394`, nouveau has an explicit call:
```c
drm_gem_gpuva_init(&nvbo->bo.base);
```
This exists because nouveau needs the list initialized *before* `ttm_bo_init_reserved()` (as the comment explains: "Subsequent bo_move() callbacks might already iterate the GEMs GPUVA list"). Previously, the core's `drm_gem_private_object_init()` would also call it (gated by the feature flag). With this patch, the core now calls it unconditionally, and then nouveau calls it again. Since it's just `INIT_LIST_HEAD()`, double-calling is harmless (re-initializing an empty list head is a no-op in effect). However, it would be tidier to also remove the now-redundant explicit call in `nouveau_bo.c` and its associated comment. This is a minor cleanup opportunity, not a correctness issue — but it would make the patch more complete.

**Summary:** The patch is correct and well-reasoned. The only suggestion is optionally removing the now-redundant `drm_gem_gpuva_init()` call in `drivers/gpu/drm/nouveau/nouveau_bo.c:394` (and its comment block at lines 391-393), since the core will now always handle this initialization.

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Generated by Claude Code Patch Reviewer