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

[Sascha Hauer]

On Mon, Dec 07, 2020 at 11:00:49AM +0100, Ahmad Fatoum wrote:
> On Mon, 2020-12-07 at 08:10 +0100, Sascha Hauer wrote:
> > 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?
> 
> I sent a fixup. I think it's ok to merge that way.

Ok, did that.

Sascha


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