drm/nouveau: check ioctl command codes better

nouveau_drm_ioctl() only checks the _IOC_NR() bits in the
DRM_NOUVEAU_NVIF command, but ignores the type and direction bits, so any
command with '7' in the low eight bits gets passed into
nouveau_abi16_ioctl() instead of drm_ioctl().

Check for all the bits except the size that is handled inside of the
handler.

Fixes: 27111a2 ("drm/nouveau: expose the full object/event interfaces to userspace")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
[ Fix up two checkpatch warnings and a typo. - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
Link: https://lore.kernel.org/r/20250711072458.2665325-1-arnd@kernel.org

Author: arndb

drivers/gpu/drm/nouveau/nouveau_drm.c

@@ -1284,6 +1284,9 @@ nouveau_ioctls[] = {
 	DRM_IOCTL_DEF_DRV(NOUVEAU_EXEC, nouveau_exec_ioctl_exec, DRM_RENDER_ALLOW),
 };
 
+#define DRM_IOCTL_NOUVEAU_NVIF _IOC(_IOC_READ | _IOC_WRITE, DRM_IOCTL_BASE, \
+				    DRM_COMMAND_BASE + DRM_NOUVEAU_NVIF, 0)
+
 long
 nouveau_drm_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 {
@@ -1297,14 +1300,10 @@ nouveau_drm_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 		return ret;
 	}
 
-	switch (_IOC_NR(cmd) - DRM_COMMAND_BASE) {
-	case DRM_NOUVEAU_NVIF:
+	if ((cmd & ~IOCSIZE_MASK) == DRM_IOCTL_NOUVEAU_NVIF)
 		ret = nouveau_abi16_ioctl(filp, (void __user *)arg, _IOC_SIZE(cmd));
-		break;
-	default:
+	else
 		ret = drm_ioctl(file, cmd, arg);
-		break;
-	}
 
 	pm_runtime_mark_last_busy(dev->dev);
 	pm_runtime_put_autosuspend(dev->dev);