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