[PATCH 11/11] doc: bcm283x: document use of mini-uart on Raspberry Pi Zero W / CM3

[Sascha Hauer]

On Sun, Nov 29, 2020 at 08:50:42PM +0100, Roland Hieber wrote:
> On Sat, Nov 28, 2020 at 10:39:34PM +0100, Ahmad Fatoum wrote:
> > As described in the UART configuration[1] article in the Raspberry Pi
> > Foundation documentation, Raspberry Pi 3 & 4 as well as Zero W use the
> > mini-uart as primary (easily user-accessible) UART. At least on the
> > Raspberry Zero W and CM3, we need to pass uart_2ndstage=1, so the
> > BootROM leaves the 8250 IP in a suitable state for use by barebox.
> > Document this.
> > 
> > [1]: https://www.raspberrypi.org/documentation/configuration/uart.md
> > 
> > Cc: Roland Hieber <rhi at pengutronix.de>
> > Cc: Rouven Czerwinski <rcz at pengutronix.de>
> > Cc: Robert Carnecky <robert at neopsis.com>
> > Cc: Andrew John <andrew at mobius-embedded-systems.co.uk>
> > Signed-off-by: Ahmad Fatoum <ahmad at a3f.at>
> > ---
> >  Documentation/boards/bcm2835.rst | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/Documentation/boards/bcm2835.rst b/Documentation/boards/bcm2835.rst
> > index c896871e0d82..dbdfc2633173 100644
> > --- a/Documentation/boards/bcm2835.rst
> > +++ b/Documentation/boards/bcm2835.rst
> > @@ -23,6 +23,13 @@ Raspberry Pi
> >           kernel=barebox.img
> >           enable_uart=1
> >  
> > +     If you want to use the mini-uart instead of the PL011, you might need to additionally set::
> > +
> > +         uart_2ndstage=1
> > +
> > +     This is useful on newer boards like the Raspberry Pi Zero W and CM3, which route the
> > +     more easily accessible primary UART to the mini-uart.
> 
> This seems to be non-optional on RPi Zero W, so I would word it more
> strongly.
> 
> With this series, at least barebox boots, which is better than in master
> :-) However, I cannot get the stock kernel (/boot/kernel.img) to boot on
> Zero W, and I cannot figure out why:

Should I wait for this being fixed before I merge this series?

Sascha

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