Commit a05d070a authored by Rahul Rameshbabu's avatar Rahul Rameshbabu Committed by David S. Miller
Browse files

ptp: Clarify ptp_clock_info .adjphase expects an internal servo to be used 



.adjphase expects a PHC to use an internal servo algorithm to correct the
provided phase offset target in the callback. Implementation of the
internal servo algorithm are defined by the individual devices.

Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: default avatarRahul Rameshbabu <rrameshbabu@nvidia.com>
Acked-by: default avatarRichard Cochran <richardcochran@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 49310624

Documentation/driver-api/ptp.rst

+16 −0
Original line number Diff line number Diff line
@@ -73,6 +73,22 @@ Writing clock drivers 
   class driver, since the lock may also be needed by the clock

   driver's interrupt service routine.



PTP hardware clock requirements for '.adjphase'

-----------------------------------------------



   The 'struct ptp_clock_info' interface has a '.adjphase' function.

   This function has a set of requirements from the PHC in order to be

   implemented.



     * The PHC implements a servo algorithm internally that is used to

       correct the offset passed in the '.adjphase' call.

     * When other PTP adjustment functions are called, the PHC servo

       algorithm is disabled.



   **NOTE:** '.adjphase' is not a simple time adjustment functionality

   that 'jumps' the PHC clock time based on the provided offset. It

   should correct the offset provided using an internal algorithm.



Supported hardware

==================

include/linux/ptp_clock_kernel.h

+4 −2
Original line number Diff line number Diff line
@@ -77,8 +77,10 @@ struct ptp_system_timestamp { 
 *            nominal frequency in parts per million, but with a

 *            16 bit binary fractional field.

 *

 * @adjphase:  Adjusts the phase offset of the hardware clock.

 *             parameter delta: Desired change in nanoseconds.

 * @adjphase:  Indicates that the PHC should use an internal servo

 *             algorithm to correct the provided phase offset.

 *             parameter delta: PHC servo phase adjustment target

 *                              in nanoseconds.

 *

 * @adjtime:  Shifts the time of the hardware clock.

 *            parameter delta: Desired change in nanoseconds.