Claude review: drm/syncobj: add drm_syncobj_timeline_signal

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

Patch Review

**Design concern**: The exported function signature is:

```c
int drm_syncobj_timeline_signal(struct drm_syncobj **syncobjs,
                                u64 user_points, u32 count)
```

`user_points` is a raw `__u64` cast from a user pointer, and the function internally does `copy_from_user(points, u64_to_user_ptr(user_points), ...)`. An exported kernel API function should not take a disguised user pointer as a `u64`. The caller (patch 12's `syncobj_ioctl_signal`) should copy the points array from userspace and pass a kernel pointer. This is the standard kernel pattern -- ioctls copy from user, then call internal functions with kernel pointers.

**Bug**: The new function adds `if (count == 0) return -EINVAL;` but the original ioctl code didn't have this check at the function level (it was checked earlier in the ioctl handler via `args->count_handles`). The semantics are preserved for the ioctl path since that check already existed, but it means the exported API differs subtly from what you might expect.

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Generated by Claude Code Patch Reviewer