rpi: Allow using PL011 UART for RPi3/RPi4
...
The Broadcom 283x SoCs feature multiple UARTs: the mostly used
"Mini-UART", which is an 8250 compatible IP, and at least one PL011.
While the 8250 is usually used for serial console purposes, it suffers
from a design flaw, where its clock depends on the VPU clock, which can
change at runtime. This will reliably mess up the baud rate.
To avoid this problem, people might choose to use the PL011 UART for
the serial console, which is pin-mux'ed to the very same GPIO pins.
This can be done by adding "miniuart-bt" to the "dtoverlay=" line in
config.txt.
To prepare for this situation, use the newly gained freedom of sharing
one console_t pointer across different UART drivers, to introduce the
option of choosing the PL011 for the console.
This is for now hard-coded to choose the Mini-UART by default.
A follow-up patch will introduce automatic detection.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Change-Id: I8cf2522151e09ff4ff94a6d396aec6fc4b091a05
Andre Przywara
committed
on 17 Mar 2020
