RPi3: serial console

[Ricardo Salveti]

On Tue, Oct 13, 2020 at 11:04 AM Peter Robinson <pbrobinson at gmail.com> wrote:
>
> > >> 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).

Noticed the same as well here (boots fine only with enable_uart=1).
While playing over with the files I noticed it works fine with the
latest firmware when using an older bcm2710-rpi-3-b-plus.dtb
(placed together with the firmware). If I use the latest
bcm2710-rpi-3-b-plus.dtb from the 5.4 downstream kernel, it doesn't
work (only tested on rpi3-b-plus).

This is with CONFIG_OF_BOARD=y, if I use CONFIG_OF_EMBED instead it
works just fine (which gives me the impression that u-boot might not
be happy with the dtb generated by the firmware when enable_uart is
not set).

Cheers,

--
Ricardo Salveti de Araujo