i am on a simple busybox-based rootfs, 4.14 imx-2.0.0 kernel, and observing a strange issue:
by a simple bash script, i am performing a simple read / write test from uart2 to uart6, and just after i perform a rpmsg m4 r/w test using the endpoint driver (ept created by echo 1 > /sys/class/rpmsg/channel_1/ept_new), after repeating 4 time the test, rpmsg channel read / write test hangs blocking execution, can exit by CTRL-.Z only and by ps i see rpmsg test process in R state.
If i remove the test on uart6, test uart2 to 5 + rpmsg works fine forever in a loop.
So seems uart6 has some special connection with rpmsg.
Also, in the imx6sx rm, after "Table 65-6. UART5 External Signals" i don't see any uart6 table, and this make me think uart6 is someway special.
I am going deeper, but if any help, welcome.