Hi David, > -----Original Message----- > From: David Henningsson [mailto:david.henningsson@xxxxxxxxxxxxx] > Sent: Thursday, November 05, 2015 5:07 PM > To: Yang, Libin; Takashi Iwai > Cc: Lin, Mengdong; Raymond Yau; airlied@xxxxxxxx; tanuk@xxxxxx; ALSA > Development Mailing List; Girdwood, Liam R; Lu, Han; Nikula, Jani > Subject: Re: DP1.2 MST audio support discussion > > > > On 2015-11-04 15:17, Yang, Libin wrote: > > + Jani, who is from Intel gfx team. > > > >> -----Original Message----- > >> From: David Henningsson [mailto:david.henningsson@xxxxxxxxxxxxx] > >> Sent: Monday, November 02, 2015 3:55 PM > >> To: Yang, Libin; Takashi Iwai > >> Cc: Lin, Mengdong; Raymond Yau; airlied@xxxxxxxx; tanuk@xxxxxx; ALSA > >> Development Mailing List; Girdwood, Liam R; Lu, Han > >> Subject: Re: DP1.2 MST audio support discussion > >> > >> > >> > >> On 2015-11-02 08:30, Yang, Libin wrote: > >>> > >>>>> 4. power management > >>>>> If we close the PCM when disconnecting monitor, the driver will > >>>> return > >>>>> -ENODEV, and we assume user space will close the PCM at once . > >>>> ... if we implement it. Actually this behavior (returning -ENODEV) is > >>>> not mandatory and needs investigation beforehand, whether this > >>>> breaks > >>>> any applications, especially PA. > >>> Yes. I heard that PA has dummy PCM and when there is no HW to > >>> play the audio, PA can smoothly move the PCM from HW to dummy > >>> PCM. If it's true, stopping PCM will not break PA, I think. > >> > >> Well, in most cases (not all) there will be an analog output available, > >> so we're more likely to move there than to a dummy PCM. The > >> problem is > >> that PA does not currently figure out that a -ENODEV means that one > >> should switch from a digital to an analog profile. So, at least at this > >> point, don't expect a "smooth move". > >> > >> I'm not sure if this is a good idea or not, but just brainstorming here: > >> > >> If PA (or other application) tries to play back to a PCM, and that PCM > >> is currently unassigned. What would happen if we actually assigned a > >> converter node at that point, but no pin node connected to that > >> converter node? Would that give a backwards compatible behaviour? > I > >> e, > >> audio userspace could successfully play back audio through the > >> converter > >> node, but then the audio goes nowhere because there is no pin node > >> assigned? > > > > GFX team hope us that if there is no monitor connected, audio > > should release gfx so gfx driver can enter power save mode. > > Based on the requirement, audio driver may need stop playback > > as soon as the monitor is disconnected. > > I'm not talking about continuous playback here, so power consumption > should not be a big concern. E g, if it takes a second or so before PA > reroutes audio somewhere else, it's not a big deal from a power save > perspective. > > 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. > > -- > David Henningsson, Canonical Ltd. > https://launchpad.net/~diwic _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
