S905X3 independent SPDIF and HDMI audio output

Hi all,

I have a S905X3 TV Box (A95X Air F3), It has SPDIF and HDMI ports. I want to play audio on both independently. But for some reason playing audio on SPDIF causes the same audio to be send to both phisical outputs. In amixer there is a control named “Spdif to HDMITX Select” toggle to “spdif”, it has two possible values, spdif and spdif_b. When set to spdif_b SPDIF and HDMI are independent but setting it to spdif makes both outputs play the same audio. When I play audio on SPDIF this control magically switches to spdif which is not what I want :confused:

this is aplay -l output (device 0 is HDMI and devices 1 is SPDIF - not device 2 which is named “SPDIF-A-dummy” - wierd):
**** List of PLAYBACK Hardware Devices ****
card 0: AMLAUGESOUND [AML-AUGESOUND], device 0: SPDIF-B-dummy dummy-0 []
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: AMLAUGESOUND [AML-AUGESOUND], device 1: TDM-B-T9015-audio-hifi T9015-audio-hifi-1 []
Subdevices: 0/1
Subdevice #0: subdevice #0
card 0: AMLAUGESOUND [AML-AUGESOUND], device 2: SPDIF-A-dummy dummy-2 []
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: AMLAUGESOUND [AML-AUGESOUND], device 3: TDM-C-dummy dummy-3 []
Subdevices: 1/1
Subdevice #0: subdevice #0

So the question is: why this “Spdif to HDMITX Select” control is toggling by itself when playing audio to SPDIF ? And how to prevent that ? Is this done by the kernel driver or by the user space ?