Re: [PATCH 12/12] misc/syncobj: add new device

[Julian Orth <ju.orth@gmail.com>]

On Sat, May 16, 2026 at 1:38 PM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> On Sat, May 16, 2026 at 01:06:15PM +0200, Julian Orth wrote:
> > This device makes the DRM_IOCTL_SYNCOBJ_* ioctls available via a
> > dedicated device. This allows applications to use syncobjs without
> > having to open device nodes in /dev/dri, on systems that don't have any
> > such nodes, or on systems whose devices don't support the
> > DRIVER_SYNCOBJ_TIMELINE feature.
> >
> > Wayland uses syncobjs as its buffer synchronization mechanism. Most
> > compositors use the DRM_IOCTL_SYNCOBJ_EVENTFD ioctl to perform a pure
> > CPU wait for syncobj point. DRM devices are not involved in this process
> > except insofar that a DRM device needs to be used to access the ioctl.
> >
> > Similarly, a software-rendered client might perform rendering on a
> > dedicated thread and use the wayland syncobj protocol to submit frames
> > before they finish rendering. Again, this does not involve DRM devices
> > except insofar ... as above.
> >
> > As an added benefit, this device removes the need to translate between
> > file descriptors and handles.
> >
> > Signed-off-by: Julian Orth <ju.orth@gmail.com>
> > ---
> >  Documentation/userspace-api/ioctl/ioctl-number.rst |   1 +
> >  drivers/misc/Kconfig                               |  10 +
> >  drivers/misc/Makefile                              |   1 +
> >  drivers/misc/syncobj.c                             | 404 +++++++++++++++++++++
> >  include/uapi/linux/syncobj.h                       |  75 ++++
> >  5 files changed, 491 insertions(+)
>
> As this is a bunch of user-facing code, why not do this in rust to at
> least get some semblance of proper parsing of user data sanity?  Or is
> the api to the drm layer just to complex for that at the moment?

I didn't consider using rust because I'm not familiar with rust in the kernel.

But even if I had considered it, I probably would not have done it
because drm_syncobj currently has no rust bindings. The driver as-is
is just a thin layer around drm_syncobj.c so if drm_syncobj gains rust
bindings it should be easy to convert the driver.

>
> Just curious, not a criticism of this in C at all.
>
> thanks,
>
> greg k-h