Harsh, ok I understand you want to completely suppress any and all serial output. As for U-Boot, this is actually a bit more complicated than it would appear, as there is no readily usable CONFIG option (or combinations thereof) that completely disables any and all serial output across SPL (MLO) and U-Boot. To provide at least an initial solution please see attached patch named "HACK: Disable all serial port input/output" that does the job by essentially neutralizing all serial port I/O functions. There are certainly other and more cleaner approaches but it is also a tradeoff of how much effort one can invest to develop such a solution. As for the Kernel, also here are several things to consider. Adding a simple "quiet" to the Kernel arguments as one might think will not be sufficient as for example it still lets critical messages through, so we need to employ a more radical approach as follows: First, you need to clear the "console=" Kernel argument which comes from the U-Boot environment (see attached patch named "HACK: am335x-evmsk: Silence Kernel log output"). Then, you need to turn off the CONFIG_SERIAL_8250_OMAP_TTYO_FIXUP Kernel config option, which would otherwise instantiate a full UART console at Kernel boot time based on the fact that you cleared out "console=". Lastly, you also need to remove the "stdout-path" property from your Kernel(!) device tree file to prevent the early console from getting instantiated implicitly. Depending on which rootfs image you boot you would still get output on the serial port after the Kernel is booted as a result of systemd (for example) starting a console session via getty, which you could disable doing this (for example): $ systemctl stop serial-getty@ttyS0.service $ systemctl disable serial-getty@ttyS0.service Hope that gives you some pointers. Regards, Andreas (Please visit the site to view this file) (Please visit the site to view this file)
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