On Wed 26 September 2012 11:35:27 Mauro Carvalho Chehab wrote:
> Em Wed, 26 Sep 2012 09:03:13 +0200
> Hans Verkuil <hverkuil@xxxxxxxxx> escreveu:
>
> > On Wed September 26 2012 04:29:33 Mauro Carvalho Chehab wrote:
> > > Em Tue, 25 Sep 2012 15:45:00 +0200
> > > Hans Verkuil <hansverk@xxxxxxxxx> escreveu:
> > >
> > > > On Tue 25 September 2012 15:33:40 Mauro Carvalho Chehab wrote:
> > > > > Em Fri, 14 Sep 2012 13:15:36 +0200
> > > > > Hans Verkuil <hans.verkuil@xxxxxxxxx> escreveu:
> > > > >
> > > > > > Fixes a v4l2-compliance error: setting audmode to a value other than mono
> > > > > > or stereo for a radio device should map to MODE_STEREO.
> > > > > >
> > > > > > Signed-off-by: Hans Verkuil <hans.verkuil@xxxxxxxxx>
> > > > > > ---
> > > > > > drivers/media/v4l2-core/tuner-core.c | 5 ++++-
> > > > > > 1 file changed, 4 insertions(+), 1 deletion(-)
> > > > > >
> > > > > > diff --git a/drivers/media/v4l2-core/tuner-core.c b/drivers/media/v4l2-core/tuner-core.c
> > > > > > index b5a819a..ea71371 100644
> > > > > > --- a/drivers/media/v4l2-core/tuner-core.c
> > > > > > +++ b/drivers/media/v4l2-core/tuner-core.c
> > > > > > @@ -1235,8 +1235,11 @@ static int tuner_s_tuner(struct v4l2_subdev *sd, struct v4l2_tuner *vt)
> > > > > > if (set_mode(t, vt->type))
> > > > > > return 0;
> > > > > >
> > > > > > - if (t->mode == V4L2_TUNER_RADIO)
> > > > > > + if (t->mode == V4L2_TUNER_RADIO) {
> > > > > > t->audmode = vt->audmode;
> > > > > > + if (t->audmode > V4L2_TUNER_MODE_STEREO)
> > > > > > + t->audmode = V4L2_TUNER_MODE_STEREO;
> > > > >
> > > > > NACK. It is not a core's task to fix driver's bugs. It would be ok to have here a
> > > > > WARN_ON(), but, if a driver is reporting a wrong radio audmode, the fix should be
> > > > > there at the drivers, and not here at the core.
> > > >
> > > > tuner-core *is* the driver.
> > >
> > > Not really... it is a driver's glue between the real I2C driver and the bridge
> > > driver.
> > >
> > > > A bridge driver just passes v4l2_tuner on to the
> > > > subdev driver(s), and it is the subdev driver such as tuner-core that needs to
> > > > process the audmode as specified by the user. Which in this case means mapping
> > > > audmodes that are invalid when in radio mode to something that is valid as per
> > > > the spec.
> > >
> > > Well, when the user is requesting an invalid mode, it should just return -EINVAL.
> > > It makes sense to add a check there at tuner-core to reject audmode if userspace
> > > is requesting, for example, a second language[1].
> >
> > My interpretation of the spec is that it will map invalid audmodes to valid audmodes.
> > From the VIDIOC_S_TUNER documentation:
> >
> > "The selected audio mode, see Table A.89, “Tuner Audio Modes” for valid values. The
> > audio mode does not affect audio subprogram detection, and like a control it does not
> > automatically change unless the requested mode is invalid or unsupported. See Table
> > A.90, “Tuner Audio Matrix” for possible results when the selected and received audio
> > programs do not match."
> >
> > So my interpretation is that if an audmode is provided that is not valid for the
> > given device, then the device maps it to something valid rather than returning an
> > error. The error code list only states that -EINVAL is returned if the index field
> > is out-of-bounds, not for invalid audmodes.
> >
> > I think this makes sense as well, otherwise apps would have to laboriously check
> > which audmodes are supported before they can call S_TUNER. It's much easier to
> > just give the 'best' audmode and let the driver downgrade if it isn't supported.
> > This is what happens today anyway, so we can't change that behavior. But the one
> > thing that should work is that the actual audmode is returned when calling G_TUNER,
> > which is why the current tuner-core fails with v4l2-compliance.
>
> Ok, you convinced me on that. Please be more verbose at the patch description,
> describing why it is falling back to a different mode.
>
> Also, please change that:
>
> > > > > > + if (t->audmode > V4L2_TUNER_MODE_STEREO)
> > > > > > + t->audmode = V4L2_TUNER_MODE_STEREO;
>
> to something like:
>
> if (t->audmode != V4L2_TUNER_MODE_STEREO &&
> t->audmode != V4L2_TUNER_MODE_MONO)
> t->audmode = V4L2_TUNER_MODE_STEREO;
>
> We use those enums/defines to not having to remember the actual numbers associated
> with them. By using operators like greater/lower than, people will actually need to
> dig into the videodev2.h, in order to know what's covered there.
>
> Besides that, the compiler will likely optimize it to greater than anyway, as audmode
> is unsigned.
>
> > > [1] Yet, I think that digital audio standards allow more than one audio channels.
> > > So, this may require to be pushed down into the drivers in some future.
> > >
> > > What is invalid actually depends on the device. For example, AM ISA drivers
> > > don't support stereo. Ok, all tuners supported by tuner-core are FM. Even so,
> > > some of them may not support stereo[2].
> > >
> > > [2] afaikt, some designs with tuner xc2028 don't support stereo. The driver currently
> > > doesn't handle such border cases, but the point is that such checks should happen
> > > at driver's level.
> >
> > 99% of all those tuner drivers do support stereo, so let's do this simple check
> > in tuner-core so we don't have to fix all of them. The spec is also clear that
> > radio devices only support mono or stereo audmodes. Those tuner drivers that
> > only support mono can easily enforce that explicitly. Or they could, if tuner-core
> > would copy back the audmode value after calling analog_ops->set_params().
>
> It makes sense to do such change, allowing drivers to override it.
I'll make the requested changes and I'll post a pull request.
Regards,
Hans
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