I have a two board. One is ls1021a-twr and other is ls1021a-iot.
When I modify UART part (uart 2, 3, 4) disabled -> okey in device tree file with ls1021a-twr, I can use uart 2, 3, 4.
But I can not use uart 2, 3, 4 in ls1021a-iot board.
I can see ttyS2, ttyS3, ttyS4. I can not send signal with minicom.
UART 2, 3, 4 is duplicated with LPUART1 (RXD, TXD, RTS, CTS) and LCD H-Sync, V-Sync signal.
In ls1021a-iot document page 12 : For full VSYNC/HSYNC support, the RCW needs to be updated to enable these signals and UART1 cannot be used. See the device errata for details.
For using UART, RCW must be modifyed?
It looks like that RCW should be changed on your board.
Check RCW on your board. Look at the Table 3-3 of the LS1021A Reference Manual:
Have a great day,