[U-Boot] Raspberry Pi Compute Module 1 mini-UART

[edrose <edrose@outramresearch.co.uk>]

Hi,

I'm working on a project that uses the Raspberry Pi Compute Module 1. Much
like the CM 3, the CM 1 has two UART interfaces - the main UART at ttyAMA0,
and a second "mini-UART" at ttyS0. The project uses the main UART since it
works better at high speeds, so the console has been bumped over to the
mini-UART. This works fine for kernel messages and as a TTY console for
logging in and interacting with the device, however I've been unable to get
u-boot to present it's console over the mini-UART.

I've worked deep enough into this to know that u-boot doesn't use the device
tree that is set-up in config.txt, so the parameters that I've put in there
to activate and remap the mini-UART (UART1 in dts files) to pins 40/41
doesn't apply to u-boot. I'm using the bcm2835-rpi-b dts file currently
since it's the best fit for the hardware, but it leaves the mini-UART port
disabled. I've tried playing around with the dts files to enable/remap the
mini-UART port however I've been unsuccessful.

Can anyone give me any pointers as to how I modify the dts files to enable
and map the second UART for u-boot to be able to use it?

Kindest regards,
Ed



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