Hello every one,
I need to enable and communicate over UART2 (PA0 & PA1) with periferial MCU device. But I'm suspecting UART2 isn't enabled !
Linux NanoPi-NEO-Air 3.4.39-h3 #2 SMP PREEMPT Tue May 23 10:32:25 CST 2017 armv7l armv7l armv7l GNU/Linux

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root@NanoPi-NEO-Air:~# dmesg | egrep "uart|tty"
[    0.000000] Kernel command line: console=ttyS0,115200 console=tty0 root=/dev/mmcblk0p2 rootwait storage_type=1 init=/sbin/init loglevel=8 partitions= selinux=0 fsck.repair=yes boot_type=1 disp_para=0 init_disp=20b0404 tv_vdid=0 fb_base=0x46400000 config_size=33968
[    0.000000] console [tty0] enabled
[    0.496761] sw_uart_get_devinfo()1503 - uart0 has no uart_regulator.
[    0.496942] sw_uart_get_devinfo()1503 - uart1 has no uart_regulator.
[    0.497116] sw_uart_get_devinfo()1503 - uart2 has no uart_regulator.
[    0.497288] sw_uart_get_devinfo()1503 - uart3 has no uart_regulator.
[    0.498065] uart0: ttyS0 at MMIO 0x1c28000 (irq = 32) is a SUNXI
[    0.498237] sw_uart_pm()890 - uart0 clk is already enable
[    0.594670] console [ttyS0] enabled
[    1.247041] uart1: ttyS1 at MMIO 0x1c28400 (irq = 33) is a SUNXI
[    1.413678] uart2: ttyS2 at MMIO 0x1c28800 (irq = 34) is a SUNXI
[    1.581918] uart3: ttyS3 at MMIO 0x1c28c00 (irq = 35) is a SUNXI
[    7.506689] systemd[1]: Created slice system-serial\x2dgetty.slice.

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cat /proc/tty/driver/uart
serinfo:1.0 driver revision:
0: uart:SUNXI mmio:0x01C28000 irq:32 tx:20983 rx:333 RTS|DTR
1: uart:SUNXI mmio:0x01C28400 irq:33 tx:0 rx:0 CTS
2: uart:SUNXI mmio:0x01C28800 irq:34 tx:0 rx:0 CTS
3: uart:SUNXI mmio:0x01C28C00 irq:35 tx:35475 rx:2373 RTS|CTS|DTR

Monitor /dev/ttyS2 with screen or byobu or ssterm
But with:

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echo "test" > /dev/ttyS2
ls > /dev/ttyS2

don't see anything.
Nor from MCU test packages....
Tried to enable UART2 with npi-config but it looks after DTB files and in that version of OS there isn't such.
Shouldn't upgrade to 4.x.y because of hardware limitations (BT.656 is needed)

IF there is matter I've tested NanoHAT OLED and it works (software installed)

Please advice how to enable UART2, thanks to anyone !