[alsa-devel] DP1.2 MST audio support discussion

[Yang, Libin]

> -----Original Message-----
> From: David Henningsson [mailto:david.henningsson at canonical.com]
> Sent: Tuesday, November 10, 2015 3:45 PM
> To: Yang, Libin; Takashi Iwai
> Cc: Lin, Mengdong; Raymond Yau; airlied at linux.ie; tanuk at iki.fi; ALSA
> Development Mailing List; Girdwood, Liam R; Lu, Han; Nikula, Jani
> Subject: Re: [alsa-devel] DP1.2 MST audio support discussion
> 
> 
> 
> On 2015-11-10 07:46, Yang, Libin wrote:
> > Hi David,
> >
> >
> >> -----Original Message-----
> >> From: David Henningsson [mailto:david.henningsson at canonical.com]
> >> Sent: Thursday, November 05, 2015 5:07 PM
> >> To: Yang, Libin; Takashi Iwai
> >> Cc: Lin, Mengdong; Raymond Yau; airlied at linux.ie; tanuk at iki.fi; ALSA
> >> Development Mailing List; Girdwood, Liam R; Lu, Han; Nikula, Jani
> >> Subject: Re: [alsa-devel] DP1.2 MST audio support discussion
> >>
> >>
> >>
> >> So I'm asking my question again. What would happen (on Intel
> hardware),
> >> if you stream audio to a converter node on the audio codec, and there
> is
> >> no pin node connected to that converter node?
> >
> > I changed the audio driver and did the test today. The test is:
> > 1. Pin 5 connect to converter 2 and playback, there is sound from pin 5.
> > 2. Pin 5 connect to converter 2 (no other pin is connected to cvt2), no
> sound.
> > 3. Pin 5 connect back to cvt 2, there is sound, playback is normal.
> >
> > And in step 2, the playback is still ongoing but no sound is out from any
> pin.
> 
> Sounds good to me, thanks for testing. Is this workaround something we
> could utilize in order to not break userspace? (This is a question for
> both you and Takashi.)
> 
> What we'll end up is essentially three types of objects:
> 
>   * PCM device (5 devices, 3,7,8,9,10)
>    - all five devices are allocated when the driver initializes

This should be for Intel platform, right? The actually number
should be:
pin number + device entry number - 1.
On intel platform, pin_num = 3, dev_num = 3, so it will be 5.

>    - all kcontrols are always bound to the PCM device (jack kctl, eld
> kctl, iec958 kctls etc)

Sure, I agree on it.

> 
>   * Monitor (pin + MST index)
>    - dynamically bound to a PCM at monitor plug-in time, according to a
> scheme that maximises the possibility for a monitor to always end up at
> the same PCM (as specified in earlier emails)
> 
>   * Converter node (3 nodes for Intel hardware)
>     - dynamically bound to a PCM at playback open time (regardless of
> whether the PCM has a monitor or not)

If so, we still need use converter on codec. This means we can't turn
off the power well in i915.

To save the power, i915 suggests that if no monitor is connected,
we should not use the HDMI codec. This means open a PCM with
no pin attached will fail. Disconnecting monitor when the corresponding
PCM is playback will trigger stop PCM.

To help move to the new method smoothly, I will add a flag.
User can decide whether to use the aggressive power saving
solution or not.

>     - return -EBUSY in case there is no free converter node

Regards,
Libin

> 
> 
> --
> David Henningsson, Canonical Ltd.
> https://launchpad.net/~diwic