Re: [PATCH v4 14/36] [media] v4l2-mc: add a function to inherit controls from a pipeline

[Steve Longerbeam]

On 03/02/2017 03:48 PM, Steve Longerbeam wrote:
> On 03/02/2017 08:02 AM, Sakari Ailus wrote:
> > Hi Steve,
> >
> > On Wed, Feb 15, 2017 at 06:19:16PM -0800, Steve Longerbeam wrote:
> > > v4l2_pipeline_inherit_controls() will add the v4l2 controls from
> > > all subdev entities in a pipeline to a given video device.
> > >
> > > Signed-off-by: Steve Longerbeam <steve_longerbeam@xxxxxxxxxx>
> > > ---
> > >  drivers/media/v4l2-core/v4l2-mc.c | 48
> > > +++++++++++++++++++++++++++++++++++++++
> > >  include/media/v4l2-mc.h           | 25 ++++++++++++++++++++
> > >  2 files changed, 73 insertions(+)
> > >
> > > diff --git a/drivers/media/v4l2-core/v4l2-mc.c
> > > b/drivers/media/v4l2-core/v4l2-mc.c
> > > index 303980b..09d4d97 100644
> > > --- a/drivers/media/v4l2-core/v4l2-mc.c
> > > +++ b/drivers/media/v4l2-core/v4l2-mc.c
> > > @@ -22,6 +22,7 @@
> > >  #include <linux/usb.h>
> > >  #include <media/media-device.h>
> > >  #include <media/media-entity.h>
> > > +#include <media/v4l2-ctrls.h>
> > >  #include <media/v4l2-fh.h>
> > >  #include <media/v4l2-mc.h>
> > >  #include <media/v4l2-subdev.h>
> > > @@ -238,6 +239,53 @@ int v4l_vb2q_enable_media_source(struct
> > > vb2_queue *q)
> > >  }
> > >  EXPORT_SYMBOL_GPL(v4l_vb2q_enable_media_source);
> > >
> > > +int __v4l2_pipeline_inherit_controls(struct video_device *vfd,
> > > +                     struct media_entity *start_entity)
> >
> > I have a few concerns / questions:
> >
> > - What's the purpose of this patch? Why not to access the sub-device node
> >   directly?
>
>
> I don't really understand what you are trying to say.<snip>

Actually I think I understand what you mean now. Yes, the user can
always access a subdev's control directly from its /dev/v4l-subdevXX.
I'm only providing this feature as a convenience to the user, so that
all controls in a pipeline can be accessed from one place, i.e. the
main capture device node.

Steve