We have a problem regarding UART (/dev/ttyS0 precisely), it seems not to work depending upon the selected SoC. By "not working", I mean that we can't even communicate (write and read) in UART.
We have five LeMaker Guitar, only two of their SoC make /dev/ttyS0 working. We thought that this was depending upon the chosen distro, but after some tests, it seems that it is not the case. We switched boards and distros many times, but in our tests we figured out that this was a problem with the SoC.
For example, we have two boards (with two SoC) that have the same Ubuntu MATE distro, but only one of them works. The last ones don't work either. The serial are well initialized in the device tree, and we are using "cutemon" to test the communication.
Have you experienced any problem with UART, regarding SoC or something else ?