@@ -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
==================
@@ -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.
.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: Rahul Rameshbabu <rrameshbabu@nvidia.com> --- Notes: Changes: v2->v1: * Removes arbitrary rule that the PHC servo must restore the frequency to the value used in the last .adjfine call if any other PHC operation is used after a .adjphase operation. Documentation/driver-api/ptp.rst | 16 ++++++++++++++++ include/linux/ptp_clock_kernel.h | 6 ++++-- 2 files changed, 20 insertions(+), 2 deletions(-)