[PATCH] drm: uapi: Add macro for chipset specific event ID region

[PATCH] drm: uapi: Add macro for chipset specific event ID region

[Bence Csokas]

uapi/drm/drm.h states:

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

However, this distinction was not put in the code. To elevate the contract
between the generic DRM framework and the driver from the comment to code,
put this in a macro for clarity and convenience.

Cc: Daniel Kiss <Daniel.Kiss@arm.com>
Signed-off-by: Bence Csokas <bence.csokas@arm.com>
---
 include/uapi/drm/drm.h         | 8 ++++++++
 include/uapi/drm/exynos_drm.h  | 4 ++--
 include/uapi/drm/virtgpu_drm.h | 2 +-
 include/uapi/drm/vmwgfx_drm.h  | 2 +-
 4 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/include/uapi/drm/drm.h b/include/uapi/drm/drm.h
index 27cc159c1d27..aa745e643ef4 100644
--- a/include/uapi/drm/drm.h
+++ b/include/uapi/drm/drm.h
@@ -1419,6 +1419,14 @@ struct drm_event {
  * The event payload is a struct drm_event_crtc_sequence.
  */
 #define DRM_EVENT_CRTC_SEQUENCE	0x03
+/**
+ * DRM_EVENT_VENDOR_SPECIFIC - vendor/chipset specific event
+ *
+ * These event IDs are reserved for chipset and driver specific events.
+ *
+ * Refer to the chipset driver's header for details and payload struct.
+ */
+#define DRM_EVENT_VENDOR_SPECIFIC(_v) ((_v) | 0x80000000)
 
 struct drm_event_vblank {
 	struct drm_event base;
diff --git a/include/uapi/drm/exynos_drm.h b/include/uapi/drm/exynos_drm.h
index a51aa1c618c1..8d3156fb129c 100644
--- a/include/uapi/drm/exynos_drm.h
+++ b/include/uapi/drm/exynos_drm.h
@@ -395,8 +395,8 @@ struct drm_exynos_ioctl_ipp_commit {
 		DRM_EXYNOS_IPP_COMMIT, struct drm_exynos_ioctl_ipp_commit)
 
 /* Exynos specific events */
-#define DRM_EXYNOS_G2D_EVENT		0x80000000
-#define DRM_EXYNOS_IPP_EVENT		0x80000002
+#define DRM_EXYNOS_G2D_EVENT		DRM_EVENT_VENDOR_SPECIFIC(0x0)
+#define DRM_EXYNOS_IPP_EVENT		DRM_EVENT_VENDOR_SPECIFIC(0x2)
 
 struct drm_exynos_g2d_event {
 	struct drm_event	base;
diff --git a/include/uapi/drm/virtgpu_drm.h b/include/uapi/drm/virtgpu_drm.h
index 9debb320c34b..03e8a0c7f778 100644
--- a/include/uapi/drm/virtgpu_drm.h
+++ b/include/uapi/drm/virtgpu_drm.h
@@ -224,7 +224,7 @@ struct drm_virtgpu_context_init {
  * effect.  The event size is sizeof(drm_event), since there is no additional
  * payload.
  */
-#define VIRTGPU_EVENT_FENCE_SIGNALED 0x90000000
+#define VIRTGPU_EVENT_FENCE_SIGNALED DRM_EVENT_VENDOR_SPECIFIC(0x10000000)
 
 #define DRM_IOCTL_VIRTGPU_MAP \
 	DRM_IOWR(DRM_COMMAND_BASE + DRM_VIRTGPU_MAP, struct drm_virtgpu_map)
diff --git a/include/uapi/drm/vmwgfx_drm.h b/include/uapi/drm/vmwgfx_drm.h
index 7d786a0cc835..5e5878384e60 100644
--- a/include/uapi/drm/vmwgfx_drm.h
+++ b/include/uapi/drm/vmwgfx_drm.h
@@ -715,7 +715,7 @@ struct drm_vmw_fence_arg {
 /*
  * The event type
  */
-#define DRM_VMW_EVENT_FENCE_SIGNALED 0x80000000
+#define DRM_VMW_EVENT_FENCE_SIGNALED DRM_EVENT_VENDOR_SPECIFIC(0x0)
 
 struct drm_vmw_event_fence {
 	struct drm_event base;
-- 
2.53.0

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

[Claude Code Review Bot]

Overall Series Review

Subject: drm: uapi: Add macro for chipset specific event ID region
Author: Bence Csokas <bence.csokas@arm.com>
Patches: 1
Reviewed: 2026-04-12T12:13:17.431218

---

This is a single patch that introduces a `DRM_EVENT_VENDOR_SPECIFIC(_v)` macro to codify the existing convention that DRM event types `>= 0x80000000` are reserved for chipset/driver-specific use. The concept is sound — elevating a comment-only contract into a code-enforced convention is good practice for UAPI headers.

However, the patch has one notable omission: `nouveau_drm.h` defines `DRM_NOUVEAU_EVENT_NVIF` as `0x80000000` (line 28) but was not converted. This appears to be because in `nouveau_drm.h` the define appears *before* the `#include "drm.h"` (line 30), so the macro wouldn't be available at the point of use. This is a valid technical obstacle, but it should be explicitly called out in the commit message. Silently skipping one of the four vendor-specific event definitions without explanation undermines the goal of making the conversion comprehensive.

The macro values are all numerically correct — every converted definition produces the same value as before.

---
Generated by Claude Code Patch Reviewer

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

[Claude Code Review Bot]

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.

---
Generated by Claude Code Patch Reviewer