Re: port-evbarm/54941: Raspberry Pi Zero W serial console corrupted when CPU frequency changed

[Rin Okuyama <rokuyama.rk%gmail.com@localhost>]

The following reply was made to PR port-evbarm/54941; it has been noted by GNATS.

From: Rin Okuyama <rokuyama.rk%gmail.com@localhost>
To: gnats-bugs%netbsd.org@localhost, Michael van Elst <mlelstv%serpens.de@localhost>
Cc: 
Subject: Re: port-evbarm/54941: Raspberry Pi Zero W serial console corrupted
 when CPU frequency changed
Date: Thu, 20 Feb 2020 11:56:28 +0900

 Thank you Michael for your comment, and sorry for the late reply.
 
 I see. The failure is due to the hardware limitation, and it is
 difficult, at least for now, to deal with it by kernel.
 
 For DTB overlay, RPI firmware requires /boot/overlays/*.dtbo files, that
 we do not currently distribute.
 
 Unfortunately, DTBO files compiled from DTS provided by github/raspberrypi:
 
    https://github.com/raspberrypi/linux/tree/rpi-4.19.y/arch/arm/boot/dts/overlays
 
 do not work. This is due to inconsistency in DTS files b/w Linux mainline
 (our upstream):
 
    https://github.com/torvalds/linux/tree/master/arch/arm/boot/dts
 
 v.s. github/raspberrypi:
 
    https://github.com/raspberrypi/linux/tree/rpi-4.19.y/arch/arm/boot/dts/
 
 # Note that firmware outputs diagnostic messages in console when dtdebug=1
 # in /boot/config.txt:
 #
 #   https://www.raspberrypi.org/documentation/configuration/device-tree.md
 #
 # and s/BOOT_UART=0/BOOT_UART=1/ in /boot/bootcode.bin:
 #
 #   https://www.raspberrypi.org/documentation/hardware/raspberrypi/bootmodes/
 
 Therefore, we need to (1) have our own DTBO files, or (2) switch to DTB
 files provided by github/raspberrypi.
 
 For (1), I cannot at the moment write working DTBO files equivalent to
 disable-bt nor miniuart-bt. I wonder whether it is possible to disable
 bluetooth node in uart0:
 
    https://nxr.netbsd.org/xref/src/sys/external/gpl2/dts/dist/arch/arm/boot/dts/bcm2835-rpi-zero-w.dts#139
 
 For (2), DTS files of github/raspberrypi cannot be compiled by our
 dtc(1), and kernel does not boot with DTB files taken from Raspbian.
 Also, changing upstream from Linux to github/raspberrypi may be not
 a good choice.
 
 Thanks,
 rin