Hello,
I’m using Buildroot to generate a custom image for RockPi4 A. My image runs main line Linux kernel (v5.10) and main line U-Boot (2021.01).
So far, all seems good, except for one of my requirements. I need to get U-Boot output on uart4 (pins 19 and 21). I have limited experience and knowledge about U-Boot so I need a little push here.
To build U-Boot, I initialize the config with rock-pi-4-rk3399_defconfig.
I thought it would just be a matter of configuration, I looked into it and found this configuration parameter:
CONFIG_DEBUG_UART_BASE
Its value is 0xFF1A0000 (address of uart2).
I changed it to 0xFF370000 (address of uart4).
Adresses deducted from reading the dts file, but it can probably be found in the board’s datasheet also.
This change had no effect, U-Boot is still writting on uart2.
I also altered the device tree source. In file arch/arm/dts/rk3399-rock-pi-4.dtsi in node chosen
I replaced
stdout-path = "serial2:1500000n8";
with
stdout-path = "serial4:1500000n8";
Now U-Boot does not output on uart2 anymore, which is good. But on uart4, I only get some ???? when I power on the board.
Note that the Linux kernel outputs log on uart4 without issue so I don’t see any reason why U-Boot could not do the same.
Also, I thought about applying the console-on-uart4 overlay, but it fails. I believe the reason is that the is no fiq-debugger node in the dts.
I don’t have high hopes that someone has already done what I’m trying to do, but maybe you guys can give me some pointers, ideas or resources that I might have missed.
Thank you!
