Hi, afaik for HDMI passthrough there should be a usable PCM mapping present for user space: aplay -L | grep hdmi hdmi:CARD=PCH,DEV=0 hdmi:CARD=PCH,DEV=1 hdmi:CARD=PCH,DEV=2 or similar. SOF with IPC4 (Meteor Lake and newer or some TGL/ADL setups with 2024.03 release) it is possible to use passthrough via HDMI technically but we are lacking the "hdmi:..." PCMs, so in reality it is not usable for applications. Afaik. So far I managed to cook up two ways of doing this, but neither one is good enough as they will create the "hdmi:..." for both IPC3 and IPC4 setups and IPC3 firmware cannot support passthrough. Setups: sof-hda-dsp cards have HDMI PCMs: pcm3-5 sof-soundwire cards have HDMI PCMs: pcm5-7 [A] use card profile Add these to /usr/share/alsa/cards/aliases.conf: sof-hda-dsp cards.sof-hda-dsp sof-soundwire cards.sof-soundwire Create the minimal sof-hda-ds.conf and sof-soundwire.conf to handle the two types of HDMI PCM numbering. [B] Using UCM https://github.com/ujfalusi/alsa-ucm-conf/tree/topic/sof-hdmi It is using the BootSequence[] to create three files: [1] /var/lib/alsa/conf.d/42-sof-hdmi.conf [2] /var/lib/alsa/card[card_number].conf.d/30-sof-hdmi-common.conf [3] /var/lib/alsa/card[card_number].conf.d/31-sof-hdmi.conf [1] includes the pcm/iec958.conf and pcm/hdmi.conf to global space of alsaconf to be used by the card macros [2] Card specific macros for hdmi PCM definition, ampping [3] Card specific definitions of the three HDMI port In both case I have the needed PCMs: aplay -L | grep hdmi hdmi:CARD=sofhdadsp,DEV=0 hdmi:CARD=sofhdadsp,DEV=1 hdmi:CARD=sofhdadsp,DEV=2 or hdmi:CARD=sofsoundwire,DEV=0 hdmi:CARD=sofsoundwire,DEV=1 hdmi:CARD=sofsoundwire,DEV=2 But it is unconditional and they will be created for all sof-hda-dsp and sof-soundwire cards. I would really appreciate some guidance on how we can achieve this correctly (the code for the UCM way leaves much to be desired, I know). How can this be done conditionally? We can set the HDMI PCMs to advertise IEC958_SUBFRAME_LE for IPC4 only, but how can we use that? Should we add some parameter to 'amixer -c0 info', like ipc_version:4/3, so if the ipc_version is 3 or missing we assume that passthrough is not supported? Thanks for the help, Péter
