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@xxxxxxxxxxxxxx> Cc: Rouven Czerwinski <rcz@xxxxxxxxxxxxxx> Cc: Robert Carnecky <robert@xxxxxxxxxxx> Cc: Andrew John <andrew@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx> Signed-off-by: Ahmad Fatoum <ahmad@xxxxxx> --- 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. + (For more information, refer to the `documentation for config.txt`_.) 5. Connect to board's UART (115200 8N1); -- 2.28.0 _______________________________________________ barebox mailing list barebox@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/barebox
