We are currently trying to get the UART3 running on the M4. After adding cases for UART3 in configure_uart_pins() / get_uart_clock_freq() it works now on the M4 when the linux kernel didn’t boot.
Issue is, after the linux boots there is just garbage on the UART3. It is already disabled in the device tree (before there was a kernel panic).
Additionally we found out, that if we wait with the initialization until the linux did boot it will work without issues. Any ideas what the issue could be?