alsa-project/alsa-ucm-conf issue #515 was edited from pv:

The configuration https://github.com/alsa-project/alsa-ucm-conf/blob/master/ucm2/USB-Audio/Foc... specifies `HWChannels 2` for the Mic1 and Mic2 devices. This gets translated to `CaptureChannels 2` for `alsaucm open '<<<SplitPCM=1>>>hw:2'`.

However, we've got a report https://gitlab.freedesktop.org/pipewire/pipewire/-/issues/4597#note_2815906 that looks like snd_pcm_hw_params_set_channels(pcm_handle, hwparams, 2) for the CapturePCM "_ucm0001.hw:Gen,0" fails with error. The PCM can be opened with 4 channels, though. Without `SplitPCM=1`, it also probably works but I'm not sure what channel count the `dshare` plugin is using.

The issue also affects the `Direct` profile, which also specifies `CaptureChannels 2`.

Is the `HWChannels 2` for Mic1/2 input direction right?

Shall `CaptureChannels 2` in UCM device be interpreted as that the device can be opened with exactly 2 channels, or that it can be opened with some number of channels >= 2?

<details>

``` $ alsaucm open '<<<SplitPCM=1>>>hw:2' dump text Verb.HiFi { Comment Default Device.Line1 { Comment "Headphones / Line 1-2" Values { CaptureCTL "_ucm0001.hw:Gen" PlaybackCTL "_ucm0001.hw:Gen" PlaybackPCM "_ucm0001.hw:Gen" PlaybackPriority 200 } } Device.Mic1 { Comment "Input 1 Mic/Inst/Line" Values { CaptureCTL "_ucm0001.hw:Gen" CaptureChannel0 0 CaptureChannelPos0 MONO CaptureChannels 2 CapturePCM "_ucm0001.hw:Gen,0" CapturePriority 200 PlaybackCTL "_ucm0001.hw:Gen" } } Device.Mic2 { Comment "Input 2 Mic/Inst/Line" Values { CaptureCTL "_ucm0001.hw:Gen" CaptureChannel0 1 CaptureChannelPos0 MONO CaptureChannels 2 CapturePCM "_ucm0001.hw:Gen,0" CapturePriority 100 PlaybackCTL "_ucm0001.hw:Gen" } } } Verb.Direct { Comment "Direct Scarlett Solo 4th Gen" Device.Direct { Comment "Direct Scarlett Solo 4th Gen" Values { CaptureCTL "_ucm0001.hw:Gen" CaptureChannels 2 CapturePCM "_ucm0001.hw:Gen" CapturePriority 1000 PlaybackCTL "_ucm0001.hw:Gen" PlaybackChannels 2 PlaybackPCM "_ucm0001.hw:Gen" PlaybackPriority 1000 } } } ```

</details>

Issue URL : https://github.com/alsa-project/alsa-ucm-conf/issues/515 Repository URL: https://github.com/alsa-project/alsa-ucm-conf