ptp: expose the programmable pins via sysfs

This patch adds the sysfs hooks needed in order to get and set the
programmable pin settings.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/ABI/testing/sysfs-ptp

@@ -54,6 +54,26 @@ Description:
 		This file contains the number of programmable periodic
 		output channels offered by the PTP hardware clock.
 
+What:		/sys/class/ptp/ptpN/n_pins
+Date:		March 2014
+Contact:	Richard Cochran <richardcochran@gmail.com>
+Description:
+		This file contains the number of programmable pins
+		offered by the PTP hardware clock.
+
+What:		/sys/class/ptp/ptpN/pins
+Date:		March 2014
+Contact:	Richard Cochran <richardcochran@gmail.com>
+Description:
+		This directory contains one file for each programmable
+		pin offered by the PTP hardware clock. The file name
+		is the hardware dependent pin name. Reading from this
+		file produces two numbers, the assigned function (see
+		the PTP_PF_ enumeration values in linux/ptp_clock.h)
+		and the channel number. The function and channel
+		assignment may be changed by two writing numbers into
+		the file.
+
 What:		/sys/class/ptp/ptpN/pps_avaiable
 Date:		September 2010
 Contact:	Richard Cochran <richardcochran@gmail.com>