Re: [PATCH 2/8] media: adv748x: add audio mute control and output selection ioctls

Alex Riesen
2020-03-13T11:01:13Z

Hans Verkuil, Fri, Mar 13, 2020 11:52:03 +0100:
> On 3/13/20 11:26 AM, Alex Riesen wrote:
> > Hans Verkuil, Fri, Mar 13, 2020 09:16:11 +0100:
> >> Generally an hdmi driver will configure the i2s audio automatically, which is
> >> typically connected to the SoC and controlled by the ALSA driver of the SoC,
> >> but there may well be missing features (audio never got a lot of attention in
> >> hdmi receivers). So what I would like to know is: what features are missing?
> >
> > Well, the audio is missing. The current adv748x driver does not export the
> > audio features of the device at all. There is no code to enable the I2S audio
> > output and it is disabled (all clock and the data lines) by default.
>
> Sorry, I was vague in my question. Obviously that needs to be added, but besides
> adding the low-level i2s support I was wondering if there are additional things
> that need to be exposed to userspace in order for audio to fully work.

None that I can't expose over the DAI interfaces: clocks, I2S format,
mute/demute ... All covered.

> >> Anything missing can likely be resolved by adding HDMI audio specific V4L2 controls,
> >> which would be the right approach for this.
> >>
> >> So I would expect to see a proposal for V4L2_CID_DV_RX_AUDIO_ controls to be
> >> added here:
> >>
> >> https://linuxtv.org/downloads/v4l-dvb-apis-new/uapi/v4l/ext-ctrls-dv.html
> >
> > This seems to be an explicitly "digital video" control class. And it has no
> > control option for mute. Or did you mean a similarly structured new class for
> > "digital audio"?
>
> There are no DV_ audio controls at all today. So any new audio controls would be
> added to the DV class. But if there is nothing that needs to be exposed, then
> nothing needs to be added :-)

Ah, alright. I shall keep an eye on it, maybe I shall find something to expose :)

Regards,
Alex