Many thanks. It appears I had completely misinterpreted the meaning of CONFIG_DEBUG_UART_CLOCK.
I see now a correct output and a new warning message: pinctrl_select_state_full: uclass_get_device_by_phandle_id: err=-19 right after "<debug_uart>" notification. Tomorrow I'll try to understand what it means. I don't think I would have found it without You pointing in the right direction. MANY Thanks! Best regards Mauro Condarelli On 1/12/20 12:58 AM, Sean Anderson wrote: > On 1/11/20 4:38 PM, Mauro Condarelli wrote: >> Thanks Joel, >> unfortunately I already have that defined, even if I forgot to copy it. >> I attach my full .config for reference as I have no idea what I'm >> still missing. >> >> On 1/11/20 9:42 PM, Sean Anderson wrote: >>>> Could You share a Linkit _defconfig with early serial debug enabled? >>>> I'm decidedly missing something as, even enabling >>>> >>>> CONFIG_DEBUG_UART=y >>>> CONFIG_DEBUG_UART_BASE=0x10000e00 >>>> CONFIG_DEBUG_UART_CLOCK=20 >>>> CONFIG_DEBUG_UART_SHIFT=2 >>>> CONFIG_DEBUG_UART_ANNOUNCE=y > So it looks like your clock is way too low. The unit for the clock is > Hz. From the device tree you sent, this board is based off > arch/mips/dts/mt7628a.dtsi, using uart2. The clock controller for this > board is compatible with "mediatek,mt7628-clk", and the driver is > located in "drivers/clk/mtmips/clk-mt7628.c". From that file, the uart2 > clock gets its frequency from CLK_SRC_PERI. Under mt7628_clk_get_rate, > the peripheral clock source depends on the value of > PERI_CLK_FROM_XTAL_SEL, which is initialized to 0 (as documented in the > data sheet). Therefore, the else clause is taken (unless configured > otherwise), so you should use 40000000 for your clock. > >>> You need to pick a debug uart driver, e.g. CONFIG_DEBUG_UART_NS16550. >> As said I have it, but I'm not sure about the other parameters. >> Maybe a better choice would be CONFIG_DEBUG_UART_MTK. >> Having a "known good" configuration would help a lot. >> >> Regards >> Mauro >> >
