From: Sérgio de Almeida Lenzi nervoso@k1.com.br Date: Sun, 22 Sep 2019 00:51:52 -0300
Hello, I am trying to setup the baud rate of the rockchip uart from the file => arch/arm/mach-rockchip/rk3328-board-tpl.c line 59 -> 63, the baud rate is at insane 1,500,000 bps... that speed it too fast for small computers using serial port to communicate with the rock64 SBC... I would like to set the baud rate at more "sane" values like 9600, 19200... or even 115200 bps
Can some one point me what values must be written to the lcr and rbr of the chip to make it happen???
arch/arm/mach-rockchip/rk3328-board-tpl.c no longer exists in the current u-boot master. There is now a arch/arm/mach-rockchip/tpl.c that is shared between various Rockchip SoCs. That file calls debug_uart_init() which end up calling _debug_uart_init() that will set the baudrate acoording to the CONFIG_BAUDRATE variable. So you can simply set CONFIG_BAUDRATE to the desired value in configs/rock64-rk3328_defconfig. Note that you'll also need to build TF-A with the appropriate baudrate setting, otherwise you will see garbled output from TF-A (or no output at all)!
I agree that 1.5 Mbps isn't really usable as a serial console speed. Many USB serial converters don't support that speed and it is way too sensitive to line noise at those speeds. Unfortunately it appears to be the default on all the newer Rockchip SoCs. For OpenBSD we always build our firmwares with CONFIG_BAUDRATE=115200, which is the de-facto standard form SBCs with ARM processors.
Cheers,
Mark
P.S. It appears that in arch/arm/mach-rockchip/rk3328/rk3328.c there is still code that initializes the baudrate. But that code shouldn't be necessary anymore.