[U-Boot] [Bug?] raspberrypi: UART issue in combination with pi3-disable-bt device-tree overlay

[Orne Brocaar]

Hello,

I ran into an issue with the UART interface and U-Boot on a Raspberry Pi 3 (rpi_3_32b_defconfig).
In my config.txt I have added the following lines:

dtparam=spi=on
enable_uart=1
core_freq=250
dtoverlay=pi3-disable-bt

This works fine when directly booting the Linux kernel, however when using U-Boot as an intermediate step,
I’m running into issues when accessing the UART interface.

As I’m using the Yocto meta-raspberrypi layer, Initially I opened a GitHub issue:
https://github.com/agherzan/meta-raspberrypi/issues/374

I was pointed to the following lines that are used in the U-Boot device-tree for the Raspberry Pi 3:
https://github.com/u-boot/u-boot/blob/master/arch/arm/dts/bcm2837-rpi-3-b.dts#L22-L34. Possibly these would
conflict with the “pi3-disable-bt” overlay.

After removing these lines, and making sure that the GPS module connected to the UART interface
would not interrupt the boot process, all works fine. See also:
https://github.com/agherzan/meta-raspberrypi/issues/374#issuecomment-457524421

Is this a bug and should this be fixed in the U-Boot repository, or is this expected behaviour and
Is patching the bcm2837-rpi-3-b.dts device-tree when using the pi3-disable-bt device-tree overlay the way to go?

Thanks!

Cheers,
Orne