Hi Fiona, On Thu, 1 Aug 2024 at 08:07, Fiona Klute <fiona.kl...@gmx.de> wrote: > > Hi everyone, > > how can I configure which of the available serial devices U-Boot will > use for its serial console? > > Background: I have a device based on a Raspberry Pi CM4, which has 6 > UARTs (UART1 is a mini UART, the others PL011) [1]. In the default > configuration (including the mainline Linux broadcom/bcm2711-rpi-cm4-io > device tree) the Bluetooth module is attached to UART0. Unless I either > completely disable UART0 (status = "disabled" in the device tree) or > reconfigure it to be a serial console (e.g. using the RPi disable-bt > DTBO) U-Boot fails to boot, I assume (it doesn't get far enough to show > messages over netconsole) because it tries and fails to set up a serial > console where there's a BT chip listening. > > That happens even if another serial console is available: With the RPi > bcm2711-rpi-cm4 DTB plus "disable-bt" (disable the Bluetooth module, > reconfigure UART0 as a serial console) and "uart1" (set up a serial > console on UART1) DTBOs I can see that U-Boot discovers the serial > device on UART1 (serial@7e215040): > > U-Boot> dm uclass serial > uclass 108: serial > 0 * serial@7e201000 @ 3af3b200, seq 0 > 1 serial@7e215040 @ 3af3b2d0, seq 1 > > However, I can't find a way to make it *use* it instead of UART0 > (serial@7e201000). I tried to set CONFIG_CONS_INDEX=1 but didn't see any > change (unfortunately the help does not describe exactly how the number > is mapped to DT UART definitions). If I completely disable UART0 in the > DT as mentioned above U-Boot uses UART1 just fine, so it's not an issue > with UART1 as such. > > To make matters slightly more complicated, the specific device I have is > a RevPi Connect 4, where a vendor overlay [2] describes how to set up an > RS485 serial console using UART5. The pins defined there are wired to > the outside of the box [3], so eventually I'll actually want to use > UART5 for the serial console. Which means I really need a (build-time or > preferably DT-based) way to configure which serial device to use. > > My goal is to create a single DTS which both U-Boot and Linux can use, > and get it upstreamed if possible. If there are configuration options > and they're just missing from the documentation, I'd be happy to send a > patch to add them once I have a solution.
You should be able to update /chosen/stdout-path (in the devicetree) to specify the UART you want, using its alias. So if you have a 'serial1' alias, you can set stdout-path to 'serial1'. This should work in Linux too. The code in question is serial_find_console_or_panic(). Regards, Simon > > Best regards, > Fiona > > [1] > https://www.raspberrypi.com/documentation/computers/configuration.html#configure-uarts > [2] > https://gitlab.com/revolutionpi/linux/-/blob/4ae9a35871799004300f83694a24359a7b4ef8fa/arch/arm/boot/dts/overlays/revpi-connect4-overlay.dts#L281-292 > [3] > https://revolutionpi.com/en/tutorials/uebersicht-revpi-connect/serielle-geraete-anschliessen-connect
