Re: DP1.2 MST audio support discussion

[Takashi Iwai <tiwai@suse.de>]

On Wed, 11 Nov 2015 08:58:29 +0100,
Yang, Libin wrote:
> 
> 
> > -----Original Message-----
> > From: Yang, Libin
> > Sent: Wednesday, November 11, 2015 10:04 AM
> > To: David Henningsson; Takashi Iwai
> > Cc: Lin, Mengdong; Raymond Yau; airlied@linux.ie; tanuk@iki.fi; ALSA
> > Development Mailing List; Girdwood, Liam R; Lu, Han; Nikula, Jani
> > Subject: RE: [alsa-devel] DP1.2 MST audio support discussion
> > 
> > 
> > > -----Original Message-----
> > > From: David Henningsson [mailto:david.henningsson@canonical.com]
> > > Sent: Tuesday, November 10, 2015 3:45 PM
> > > To: Yang, Libin; Takashi Iwai
> > > Cc: Lin, Mengdong; Raymond Yau; airlied@linux.ie; tanuk@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@canonical.com]
> > > >> Sent: Thursday, November 05, 2015 5:07 PM
> > > >> To: Yang, Libin; Takashi Iwai
> > > >> Cc: Lin, Mengdong; Raymond Yau; airlied@linux.ie; tanuk@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.
> 
> In  hdmi_pcm_open(), it will judge whether pin_idx is valid, 
> if not it will return -EINVAL. So for dynamic PCM assignment,
> open will fail if no monitor is connected.
> 
> If we want to support open on PCM without monitor, many
> code must be rewrited. And it seems open a PCM without
> monitor is not a good behavior. As Raymond said in previous
> email, For alt analog playback device , it return EBUSY when
> DAC of HP is not available. I think for HDMI audio we can
> have the aligned behavior? And -ENODEV may be better.

Libin, it's why I've been repeated asking to split the patches,
instead of posting a big iron patch.  Then we can test and evaluate
whether this part is really working in general.


Takashi