PREEMPT_RT with Linux 4.4.21 on VF61 with BSP 2.6.1 - Problems with M4 using Remoteproc

@stefan.tx, the dmesg | head has shown me the following data:
Linux version 4.4.48-rt63-00424-gc9bd85a938f7-dirty

With a git log on my linux-toradex repo, I’ve seen that this correspond to the “c9bd85a9” hash, the last commit from the 4.4-next.

Regarding boot freezes: They originate from the TTY (lpuart) driver. Beside using the latest version from the 4.4 -next branch (which includes the re-synced tty driver) you need to apply the following patch: fsl_lpuart_lock.patch

@andrecurvello, I think I found & fixed the issue, I created a new answer. I yet need to understand why we never see this in non-preempt rt kernels and whether the fix should be part of standard driver or not.