On Wed, 04 Nov 2015, "Yang, Libin" <libin.yang@xxxxxxxxx> 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. Rather, as soon as the userspace responding to hotplug uevents has reacted and disabled the display. See [1] for a better explanation. In other words, it would be desirable that you call the put power hook in response to intel_audio_codec_disable(). BR, Jani. [1] https://bugs.freedesktop.org/show_bug.cgi?id=90447#c19 > >> >> (Or perhaps we PA developers should actually start supporting this >> properly like we said that we should do, for like three years or >> something...) >> >> // David > -- Jani Nikula, Intel Open Source Technology Center _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
