Wait, is this saying you will have exactly one PCM device/FE DAI connected to the USB BE DAI exposed in patch 11?
+ SND_SOC_DAPM_MIXER("USB Mixer", SND_SOC_NOPM, 0, 0, + usb_mixer_controls, + ARRAY_SIZE(usb_mixer_controls)),
And then what is the role of the USB mixer if you only have one input?
I must be missing something.
Not sure if this is a QCOM specific implementation, but the way the DT is defined for the USB offload path is as follows:
usb-dai-link { link-name = "USB Playback";
cpu { sound-dai = <&q6afedai USB_RX>; };
codec { sound-dai = <&usbdai USB_RX>; };
platform { sound-dai = <&q6routing>; }; };
Based on our DT parser helper API (qcom_snd_parse_of()) this isn't going to create a PCM device. The PCM devices are created for nodes that don't have a codec and platform defined:
mm1-dai-link { link-name = "MultiMedia1"; cpu { sound-dai = <&q6asmdai MSM_FRONTEND_DAI_MULTIMEDIA1>; }; };
The ASM path is the entity that defines the number of PCM devices that is created for the QC ASoC platform card, and is where the actual PCM data is sent over to the DSP. So there could be several PCM devices that can use the USB BE DAI.
ok, but then how would this work with the ALSA controls reporting which PCM device can be used? I didn't see a mechanism allowing for more than one offloaded device, IIRC the control reported just ONE PCM device number.