ptp: clarify the clock_name sysfs attribute

There has been some confusion among PHC driver authors about the
intended purpose of the clock_name attribute. This patch expands the
documation in order to clarify how the clock_name field should be
understood.
Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/ABI/testing/sysfs-ptp

@@ -19,7 +19,11 @@ Date:		September 2010
 Contact:	Richard Cochran <richardcochran@gmail.com>
 Description:
 		This file contains the name of the PTP hardware clock
-		as a human readable string.
+		as a human readable string. The purpose of this
+		attribute is to provide the user with a "friendly
+		name" and to help distinguish PHY based devices from
+		MAC based ones. The string does not necessarily have
+		to be any kind of unique id.
 
 What:		/sys/class/ptp/ptpN/max_adjustment
 Date:		September 2010

include/linux/ptp_clock_kernel.h

@@ -42,7 +42,9 @@ struct ptp_clock_request {
  * struct ptp_clock_info - decribes a PTP hardware clock
  *
  * @owner:     The clock driver should set to THIS_MODULE.
- * @name:      A short name to identify the clock.
+ * @name:      A short "friendly name" to identify the clock and to
+ *             help distinguish PHY based devices from MAC based ones.
+ *             The string is not meant to be a unique id.
  * @max_adj:   The maximum possible frequency adjustment, in parts per billon.
  * @n_alarm:   The number of programmable alarms.
  * @n_ext_ts:  The number of external time stamp channels.