Re: [PATCH] tuner-core: return tuner name with ioctl VIDIOC_G_TUNER

[Hans Verkuil <hverkuil@xs4all.nl>]

On Wed January 23 2013 16:57:40 Frank Schäfer wrote:
> Am 23.01.2013 08:35, schrieb Hans Verkuil:
> > On Tue January 22 2013 20:46:21 Frank Schäfer wrote:
> >> tuner_g_tuner() is supposed to fill struct v4l2_tuner passed by ioctl
> >> VIDIOC_G_TUNER, but misses setting the name field.
> >>
> >> Signed-off-by: Frank Schäfer <fschaefer.oss@googlemail.com>
> >> Cc: stable@kernel.org
> >> ---
> >>  drivers/media/v4l2-core/tuner-core.c |    1 +
> >>  1 Datei geändert, 1 Zeile hinzugefügt(+)
> >>
> >> diff --git a/drivers/media/v4l2-core/tuner-core.c b/drivers/media/v4l2-core/tuner-core.c
> >> index b5a819a..95a47cf 100644
> >> --- a/drivers/media/v4l2-core/tuner-core.c
> >> +++ b/drivers/media/v4l2-core/tuner-core.c
> >> @@ -1187,6 +1187,7 @@ static int tuner_g_tuner(struct v4l2_subdev *sd, struct v4l2_tuner *vt)
> >>  
> >>  	if (check_mode(t, vt->type) == -EINVAL)
> >>  		return 0;
> >> +	strcpy(vt->name, t->name);
> >>  	if (vt->type == t->mode && analog_ops->get_afc)
> >>  		vt->afc = analog_ops->get_afc(&t->fe);
> >>  	if (analog_ops->has_signal)
> >>
> > Nacked-by: Hans Verkuil <hans.verkuil@cisco.com>
> >
> > And the reason is that the tuner field should be filled in by the bridge
> > driver. That's because you may have multiple tuners and it's only the
> > bridge driver that will know which tuner is which and what name to give
> > it.
> 
> Hmmm... I don't understand.
> Isn't his a per-tuner (subdev) operation ? If a device has multiple
> tuners (subdevs) it is called for each of them.
> So how can the returned tuner name be wrong and why should the bridge
> driver know better than the subdevice itself which name is correct ?

The name that's filled in is exposed to userspace, so it should be something
meaningful and not some internal name. In the case of multiple tuners that
means that the name should be something like 'TV 1' or 'TV 2', where the name
matches a name (label) of a tuner input of the product. There is no way a
subdev driver can know that, only the bridge driver knows what product it is
and thus what the labels on the inputs are.

It is somewhat theoretical since we don't have any multi-tuner devices (yet),
so for now names like 'Radio' and 'TV' are sufficient, but we made the same
mistake (letting subdevs set the name) in the past for regular video/audio
inputs and outputs and it took a lot of work to fix that.

The golden rule is that sub-devices should not assume anything about how they
are hooked up in the actual product.

Regards,

	Hans