Attaching an I2C VCM subdev (media entity) to media pipeline

Attaching an I2C VCM subdev (media entity) to media pipeline

[Karthik Poduval]

Hi All,

I had a question about VCM subdev (media entity). The  example VCM
drivers have no pads. How do we attach them to the image sensor subdev
in the pipeline ?

-- 
Regards,
Karthik Poduval

Re: Attaching an I2C VCM subdev (media entity) to media pipeline

[Daniel Scally]

Hi Karthik

On 07/06/2022 18:29, Karthik Poduval wrote:
> Hi All,
>
> I had a question about VCM subdev (media entity). The  example VCM
> drivers have no pads. How do we attach them to the image sensor subdev
> in the pipeline ?
>
This is somewhat in its infancy so you'll need to be running v5.19-rc1,
but assuming you're describing the device with DT you should be able to
link them by providing a lens-focus property with a phandle pointing to
the node for the lens controller. No pad-to-pad links will or should be
created though, the connection is represented by an "ancillary link"
which should be created by v4l2-core. The VCM drivers won't be in the
image pipeline as such but their connection to the sensor subdev is
discoverable to user space when parsing links, for example in
libcamera's implementation:
https://git.linuxtv.org/libcamera.git/tree/src/libcamera/media_device.cpp#n732

Re: Attaching an I2C VCM subdev (media entity) to media pipeline

[Kieran Bingham]

Hi Karthik,

Quoting Karthik Poduval (2022-06-07 18:29:23)
> Hi All,
> 
> I had a question about VCM subdev (media entity). The  example VCM
> drivers have no pads. How do we attach them to the image sensor subdev
> in the pipeline ?

This requires a bit of support that was added fairly recently for
managing non-data links between subdevices. This was added through the
use of 'ancillary links' which can connect a sensor and a VCM.

It should be handled automatically if you're on the latest kernel
version, but if not you would perhaps need to back-port the
implementation. I believe it's handled automatically through the async
subdevice notifier systems.

> -- 
> Regards,
> Karthik Poduval

--
Kieran

Re: Attaching an I2C VCM subdev (media entity) to media pipeline

[Karthik Poduval]

Thank you Daniel and Kieran,

Will take a look at the ancillary links and try to backport.

--
Regards,
Karthik Poduval

On Tue, Jun 7, 2022 at 2:36 PM Kieran Bingham
<kieran.bingham@ideasonboard.com> wrote:
>
> Hi Karthik,
>
> Quoting Karthik Poduval (2022-06-07 18:29:23)
> > Hi All,
> >
> > I had a question about VCM subdev (media entity). The  example VCM
> > drivers have no pads. How do we attach them to the image sensor subdev
> > in the pipeline ?
>
> This requires a bit of support that was added fairly recently for
> managing non-data links between subdevices. This was added through the
> use of 'ancillary links' which can connect a sensor and a VCM.
>
> It should be handled automatically if you're on the latest kernel
> version, but if not you would perhaps need to back-port the
> implementation. I believe it's handled automatically through the async
> subdevice notifier systems.
>
> > --
> > Regards,
> > Karthik Poduval
>
> --
> Kieran



-- 
Regards,
Karthik Poduval