Hi. After checking the schematic, ROCK Pi N10 uses UART2 Channel C for debug console by default.
if you want to use U-Boot console, try to add this patch for U-Boot.
36 diff --git a/arch/arm/mach-rockchip/rk3399/rk3399.c b/arch/arm/mach-rockchip/rk3399/rk3399.c
37 index ba5f731..f658a39 100644
38 --- a/arch/arm/mach-rockchip/rk3399/rk3399.c
39 +++ b/arch/arm/mach-rockchip/rk3399/rk3399.c
40 @@ -140,16 +140,16 @@ void board_debug_uart_init(void)
41 rk_clrsetreg(&grf->gpio4c_iomux,
42 GRF_GPIO4C4_SEL_MASK,
43 GRF_UART2DBGC_SOUT << GRF_GPIO4C4_SEL_SHIFT);
44 -#if defined(CONFIG_ROCKCHIP_RK3399PRO)
45 - /* Set channel A as UART2 input */
46 - rk_clrsetreg(&grf->soc_con7,
47 - GRF_UART_DBG_SEL_MASK,
48 - GRF_UART_DBG_SEL_A << GRF_UART_DBG_SEL_SHIFT);
49 -#else
50 +//#if defined(CONFIG_ROCKCHIP_RK3399PRO)
51 +// /* Set channel A as UART2 input */
52 +// rk_clrsetreg(&grf->soc_con7,
53 +// GRF_UART_DBG_SEL_MASK,
54 +// GRF_UART_DBG_SEL_A << GRF_UART_DBG_SEL_SHIFT);
55 +//#else
56 /* Set channel C as UART2 input */
57 rk_clrsetreg(&grf->soc_con7,
58 GRF_UART_DBG_SEL_MASK,
59 GRF_UART_DBG_SEL_C << GRF_UART_DBG_SEL_SHIFT);
60 -#endif
61 +//#endif
62 #endif
63 }