Support option to disable serial console output

[ruifung]

Having the kernel output to ttyAMA0 prevents usage of the UART interface.

Would be good to have an option to disable that, if the Pi in question has some device attached to ttyAMA0, for example a conbee2 zigbee adapter.

[ruifung]

Also to note: U-boot by default also outputs to serial console, I suspect this is what is causing issues when you have devices attached on the pi4's primary serial output.

[ruifung]

I've been trying to patch u-boot to stop it writing output to serial, but all the instructions I find online can't seem to deal with this

[frezbo]

I think its disabled using the bt overlay in congix.txt and passing -console args when generating the image

[ruifung]

what about the u-boot output? I've managed to disable everything except the output from the initial u-boot loading, and I believe this overlay sets the bt overlay by default?

[frezbo]

https://github.com/siderolabs/sbc-raspberrypi/blob/main/installers/rpi_generic/src/config.txt#L15 set this to 0

[ruifung]

I'll give that a try later then, but I was under the understanding that doing that would disable UART functionality from being accessible inside the OS...?

[frezbo]

I'll give that a try later then, but I was under the understanding that doing that would disable UART functionality from being accessible inside the OS...?

maybe try this https://github.com/raspberrypi/firmware/blob/master/boot/overlays/README#L3279, seems there's no overlay to completely disable serial, otherwise have to compile a custom u-boot

[frezbo]

seems this might work: https://github.com/raspberrypi/firmware/blob/master/boot/overlays/README#L4781

[ruifung]

I'm not trying to disable serial completely, just suppress all bootup output. But yeah. I guess I need to look into u-boot patches to try to suppress it's output.