[pulseaudio-discuss] HDA HDMI audio PCM names
kai.vehmanen at linux.intel.com
Tue Aug 27 14:39:16 UTC 2019
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:
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?
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