RPi3: serial console

[Peter Robinson]

> >> Hello Matthias,
> >>
> >> I have upgraded the Raspberry 3 firmware from raspi3-firmware
> >> (1.20190215-1+deb10u4) to raspi-firmware (1.20200601-3)
> >> [https://packages.debian.org/bullseye/raspi-firmware].
> >>
> >> After the upgrade the output of U-Boot on the serial console is complete
> >> gibberish as if the baudrate were incorrect. The output from the Linux
> >> kernel is fine at 115200 baud.
> >
> > I've seen similar on all firmware since around mid April up until
> > recently, it seems to be fixed with releases in Oct (I'm using one
> > from Oct 8th), I'm not sure if it can be fixed in U-Boot but it seems
> > to be due to a change in the firmware.
>
> Thanks for confirming the problem.

For reference I have found a number of other problems with recent
firmwares and 2020.10 release:
* U-Boot crashes on a RPi4 8Gb model if you don't have a display connected [1]
* It doesn't boot, not sure if it's a crash or something else, you
just get the rainbow screen, if you don't have the uart enabled in
config.txt (ie just using a display for output).

Both of these seem to be due to firmware changes as opposed to U-Boot
changes, as it was working fine on the firmware from Apr 1st, but
there's been various other issues there like the 8Gb model doesn't
completely work.

[1] https://lists.denx.de/pipermail/u-boot/2020-September/428156.html

> Using the most current files from
> https://github.com/raspberrypi/firmware does not solve the problem for me.
>
> In bcm283x_mu_serial_setbrg() we divide a clock rate by the baudrate.
> divider = plat->clock / (baudrate * 8);
>
> If we do not have the correct clock rate, the actual baudrate will be wrong.
>
> Best regards
>
> Heinrich
>
> >
> >> I observe this both with rpi_3_defconfig and rpi_arm64_defconfig,
> >> v2020.10 and current origin/master.
> >>
> >> config.txt:
> >>
> >> arm_control=0x200
> >> enable_uart=1
> >> upstream_kernel=1
> >> kernel=u-boot.bin
> >>
> >> boot.scr:
> >> setenv autoload no
> >> dhcp
> >> load mmc 0:1 $fdt_addr_r bcm2710-rpi-3-b-plus.dtb
> >> load mmc 0:2 $kernel_addr_r EFI/debian/grubaa64.efi
> >> bootefi $kernel_addr_r $fdt_addr_r
> >>
> >> Best regards
> >>
> >> Heinrich
>