On Tue, 2019-08-27 at 17:39 +0300, Kai Vehmanen wrote: > Hi all, > > we are considering removing the backup-PCM logic from snd_hda_intel > HDMI/DP audio driver (note: this is used for wide variety of HDA > controllers, not just Intel ones). See mail thread on alsa-devel: > > https://mailman.alsa-project.org/pipermail/alsa-devel/2019-August/154561.html > > In short, with DisplayPort-MST, additional monitors connected to a MST > hub, and/or to monitor upstream DP ports, these would be routed to > separate ALSA PCMs, e.g. PCM9 and PCM10, leaving the "standard" PCM > numbers free for non-MST monitors. > > This is getting highly problematic, especially when we support HDMI audio > with systems that have a DSP, and the PCM<->HDMI-audio-converter mapping > can be essentially arbitrary. The proposal is to just expose N pieces > of PCMs (N number of converters in hw, e.g. 3 with i915), and any > connected monitor (MST or not), is roured to one these PCMs. > > Tanu added the ELD autodetect support in PA-12.x, and after that, HDA + PA > works pretty nicely even without the backup PCMs, and a non-standard PCM > device numbering for HDMI audio. > > Now, I'm writing here as some kernel devs have referred to Pulseaudio > as the source for the requirement to map MST monitors to the > backup/virtual PCMs. Can anyone of you recall what was this about? I don't recall, in fact I don't even remember hearing about the "backup PCM" concept before. As far as I can tell, PulseAudio imposes or has imposed the following limitations: * PCMs can't be added and removed dynamically on a card. PulseAudio doesn't have support for dynamic PCMs. * Previously HDMI jack detection required that specific PCM numbers are used, but as you noted, we have autodetection for this now. * The "hdmi:x,y" PCM devices must exist in the alsa configuration, bare "hw:x,z" won't be detected properly. -- Tanu https://www.patreon.com/tanuk https://liberapay.com/tanuk _______________________________________________ pulseaudio-discuss mailing list pulseaudio-discuss@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/pulseaudio-discuss
