From c06cd360830e83d4d916da3918a4f819d59230e9 Mon Sep 17 00:00:00 2001 From: Ahmad Fatoum Date: Sat, 28 Nov 2020 22:39:34 +0100 Subject: doc: bcm283x: document use of mini-uart on Raspberry Pi Zero W / CM3 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 Cc: Rouven Czerwinski Cc: Robert Carnecky Cc: Andrew John Signed-off-by: Ahmad Fatoum Signed-off-by: Sascha Hauer --- Documentation/boards/bcm2835.rst | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'Documentation/boards') diff --git a/Documentation/boards/bcm2835.rst b/Documentation/boards/bcm2835.rst index c896871e0d..8af6a09c13 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 may need to additionally set:: + + uart_2ndstage=1 + + This is required on boards, like the Raspberry Pi Zero W, that use the mini-uart as the + primary UART. It is needed on boards like the CM3 as well if the mini-uart is to be used. + (For more information, refer to the `documentation for config.txt`_.) 5. Connect to board's UART (115200 8N1); -- cgit v1.2.1