CHDMISoundBaseDevice feature extension up to 8ch.

[Newdrake]

May be useful for professional audio application the extension of the audio channels of the circle class CHDMISoundBaseDevice from actual limits of 2ch up to 8ch.
Trying to implement this feature extension I've searched for the necessary changes to do.
There are many define in the code fixing this limit, SOUND_HW_CHANNELS WRITE_CHANNELS and also some value in the SetAudioInfoFrame method, but also modifying these value to the new expect correct value the driver doesn't work correctly.
On the other side, it seem not available the technical documentation of the HDMI internal peripheral of BCM2711 to have a clear way on how to set the correct parameters in the registers to upgrade the number of channels.
There is also a Linux implementation of this driver working up to 8ch but the implementation is completely different and not very easy to derive from this the modification needed in the Circle code.
I am asking for suggestion for the right strategy to do this.

[rsta2]

You could do an insensitive search for "chan" in the file drivers/gpu/drm/vc4/ vc4_hdmi.c in Linux and look for the same registers in the Circle driver, when you have a match. But there is also the HDMI display driver in this file, so not all matches will be important for HDMI audio. I guess you have to modify soundbasedevice.cpp too, where SoundFormatIEC958 is found. You must use the standard constructor of CSoundBaseDevice in CHDMISoundBaseDevice and explicitly call CSoundBaseDevice::Setup() to be able to use 8 channels.

[Newdrake]

Thanks a lot for your useful guiding indication, now the CHDMISoundBaseDevice driver is working with 8 channels!
In my application I need two instance of the CSoundBaseDevice class, one for I2S and one for HDMI, but when using the .write method of HDMI instance the audio system collapse, there could be any conflict between this two instances at m_Interrupt or DMA level?

[rsta2]

Great, you got it working with 8 channels! I'm not aware of a conflict, but you will have twice the IRQs in a time interval.