ice: add ice driver PTP pin documentation

Add a description of PTP pins support by the adapters to ice driver
documentation.

Reviewed-by: Milena Olech <[e-mail]>
Signed-off-by: Karol Kolacinski <[e-mail]>
Signed-off-by: Arkadiusz Kubalewski <[e-mail]>
Tested-by: Rinitha S <[e-mail]> (A Contingent worker at Intel)
Reviewed-by: Simon Horman <[e-mail]>
Signed-off-by: Tony Nguyen <[e-mail]>

Documentation/networking/device_drivers/ethernet/intel/ice.rst

···
 
   # ethtool -K <ethX> tx-udp-segmentation [off|on]
 
+PTP pin interface
+-----------------
+All adapters support standard PTP pin interface. SDPs (Software Definable Pin)
+are single ended pins with both periodic output and external timestamp
+supported. There are also specific differential input/output pins (TIME_SYNC,
+1PPS) with only one of the functions supported.
+
+There are adapters with DPLL, where pins are connected to the DPLL instead of
+being exposed on the board. You have to be aware that in those configurations,
+only SDP pins are exposed and each pin has its own fixed direction.
+To see input signal on those PTP pins, you need to configure DPLL properly.
+Output signal is only visible on DPLL and to send it to the board SMA/U.FL pins,
+DPLL output pins have to be manually configured.
 
 GNSS module
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