Fwd: Add method to allow switching kernel level PPS signal from DCD to CTS serial pin

[Bagas Sanjaya]

Hi Greg, hi maintainers,

On Bugzilla, Elvis <elvisimprsntr@xxxxxxxxx> requested a new RJ45 UART
feature [1]:

> BACKGROUND
> 
> There are appliances that do not have a full DE9 RS-232 port and only RJ45 COM ports, which do not include the DCD pin required for PPS signal detection.  
> 
> RJ45 COM port do include the CTS input pin #8, which can be used for PPS signal detection.  This is a feature that has been available in FreeBSD for some time.  
> 
> https://man.freebsd.org/cgi/man.cgi?query=uart
> 
> FreeBSD allows switching from DCD to CTS pin on the fly using a system tunable in a loader.conf file.  Example: dev.uart.0.pps_mode="1"
> 
> This allow one to connect a serial GPS receiver with PPS output to a RJ45 COM port for a Stratum 0 GPS+PPS source.  
> 
> https://github.com/elvisimprsntr/pfsense-ntp-gps?tab=readme-ov-file
> 
> KERNAL PATCH HACKS
> 
> Some kernel patches have demonstrated receiving PPS on the CTS pin, but requires hacking up the kernel and will will not persist on kernel update to new installations.  
> 
> https://github.com/not1337/pps-stuff
> 
> FEATURE REQUEST
> 
> Add a tunable option to allow the end user to switch between PPS on DCD to CTS pin, similar to the way FreeBSD does.

What do you think about above feature request?

Thanks.

[1]: https://bugzilla.kernel.org/show_bug.cgi?id=218813

-- 
An old man doll... just what I always wanted! - Clara

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