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

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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(+)
> 
> diff --git a/Documentation/userspace-api/ioctl/ioctl-number.rst b/Documentation/userspace-api/ioctl/ioctl-number.rst
> index 331223761fff..5e140ae5735e 100644
> --- a/Documentation/userspace-api/ioctl/ioctl-number.rst
> +++ b/Documentation/userspace-api/ioctl/ioctl-number.rst
> @@ -395,6 +395,7 @@ Code  Seq#    Include File                                             Comments
>                                                                         <mailto:michael.klein@puffin.lb.shuttle.de>
>  0xCC  00-0F  drivers/misc/ibmvmc.h                                     pseries VMC driver
>  0xCD  01     linux/reiserfs_fs.h                                       Dead since 6.13
> +0xCD  00-0F  uapi/linux/syncobj.h
>  0xCE  01-02  uapi/linux/cxl_mem.h                                      Compute Express Link Memory Devices
>  0xCF  02     fs/smb/client/cifs_ioctl.h
>  0xDD  00-3F                                                            ZFCP device driver see drivers/s390/scsi/
> diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
> index 00683bf06258..c1e7749bd356 100644
> --- a/drivers/misc/Kconfig
> +++ b/drivers/misc/Kconfig
> @@ -644,6 +644,16 @@ config MCHP_LAN966X_PCI
>  	    - lan966x-miim (MDIO_MSCC_MIIM)
>  	    - lan966x-switch (LAN966X_SWITCH)
>  
> +config SYNCOBJ_DEV
> +	tristate "DRM syncobj device (/dev/syncobj)"
> +	depends on DRM

If this is a drm-only thing, then please put it in the drm subdirs, not
in drivers/misc/ as that would imply that I have to maintain this, not
the DRM developers :)

thanks,

greg k-h