Claude review: drm: uapi: Add macro for chipset specific event ID region

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

Patch Review

**Value correctness — OK**

All conversions are value-preserving:
- `DRM_EXYNOS_G2D_EVENT`: `0x0 | 0x80000000 = 0x80000000` (was `0x80000000`) ✓
- `DRM_EXYNOS_IPP_EVENT`: `0x2 | 0x80000000 = 0x80000002` (was `0x80000002`) ✓
- `VIRTGPU_EVENT_FENCE_SIGNALED`: `0x10000000 | 0x80000000 = 0x90000000` (was `0x90000000`) ✓
- `DRM_VMW_EVENT_FENCE_SIGNALED`: `0x0 | 0x80000000 = 0x80000000` (was `0x80000000`) ✓

**Missing conversion — nouveau_drm.h**

```c
/* nouveau_drm.h line 28 */
#define DRM_NOUVEAU_EVENT_NVIF                                       0x80000000
```

This is a vendor-specific event at `0x80000000` that was not converted. The cause is likely the include ordering in `nouveau_drm.h`:

```c
/* line 28 */ #define DRM_NOUVEAU_EVENT_NVIF   0x80000000
/* line 30 */ #include "drm.h"
```

The macro isn't defined yet at line 28. The fix would be to move the `#include "drm.h"` above the define, or move the define below the include. Either way, this omission should be mentioned in the commit message, or better yet, fixed as part of this patch.

**Comment update opportunity**

The existing comment at `drm.h:1387`:

```c
 * Event types 0 - 0x7fffffff are generic DRM events, 0x80000000 and
 * up are chipset specific.
```

could be updated to reference the new `DRM_EVENT_VENDOR_SPECIFIC()` macro, reinforcing the link between the comment and the code it describes. This is optional but would improve discoverability.

**Macro design — minor concern**

```c
#define DRM_EVENT_VENDOR_SPECIFIC(_v) ((_v) | 0x80000000)
```

The OR operation doesn't guard against a caller passing a value that already has bit 31 set (e.g., `DRM_EVENT_VENDOR_SPECIFIC(0x80000000)` would produce `0x80000000`, silently masking a likely error). For UAPI this is probably fine — adding `BUILD_BUG_ON` style validation would be impractical in a header — but it's worth noting.

**Naming**

`DRM_EVENT_VENDOR_SPECIFIC` reads somewhat like a constant rather than a function-like macro. Names like `DRM_EVENT_VENDOR(_v)` or `DRM_VENDOR_EVENT(_v)` might be slightly more conventional, but this is a subjective style point and the current name is descriptive enough.

**Summary**: The patch is a net improvement in code clarity. The missing `nouveau_drm.h` conversion is the main issue — it should either be included (with the necessary include reorder) or explicitly explained in the commit message. With that addressed, the patch looks ready.

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Generated by Claude Code Patch Reviewer