Re: [PATCH RFC 5/5] media: imx219: Add status polling using .detect()

[Sakari Ailus <sakari.ailus@linux.intel.com>]

Hi Dave, Mattij,

On Thu, Oct 01, 2026 at 04:58:57PM +0100, Dave Stevenson wrote:
> Hi Mattij
> 
> On Thu, 1 Oct 2026 at 13:55, Mattijs Korpershoek
> <mkorpershoek@kernel.org> wrote:
> >
> > Userspace needs to be notified when a sensor connection status
> > changes (e.g. disconnected at boot, then later reconnected) so it can
> > react accordingly.
> >
> > Add periodic polling using a delayed work that calls .detect() every
> > 2s and sends a KOBJ_CHANGE uevent with HOTPLUG=1 on status changes.
> > This mirrors the approach used by DRM connectors in output_poll_execute().
> 
> AIUI DRM polls from within the framework (drm_probe_helper.c), not by
> a workqueue in the individual drivers.
> 
> Admittedly V4L2 doesn't currently have a totally obvious place to
> setup this, but it would be far less effort to have the polling
> framework within the core code rather than driver.
> Possibly initialised in __v4l2_async_register_subdev_sensor() based on
> whether .detect is set, and cleaned up in
> v4l2_async_unregister_subdev, with the workqueue calling .detect and
> generating the udev event based on the return value? I think that's
> feasible.

Sounds good to me.

I'd also put this behind a Kconfig option, the use case is rather special.

Also there are different approaches to this: in some cases you may want to
know the values written to the device's registers get updated so you write
and read, then some devices might crash in a way they're not doing their
real job while still allowing reading registers as usual. These are rare
cases though.

Should the interval be at least configurable? That indeed further suggests
the use of controls for this.

-- 
Regards,

Sakari Ailus