iavf: periodically cache PHC time

JIRA: https://issues.redhat.com/browse/RHEL-83568

commit 7c01dbf
Author: Jacob Keller <jacob.e.keller@intel.com>
Date:   Wed Nov 6 12:37:25 2024 -0500

    iavf: periodically cache PHC time

    The Rx timestamps reported by hardware may only have 32 bits of storage
    for nanosecond time. These timestamps cannot be directly reported to the
    Linux stack, as it expects 64bits of time.

    To handle this, the timestamps must be extended using an algorithm that
    calculates the corrected 64bit timestamp by comparison between the PHC
    time and the timestamp. This algorithm requires the PHC time to be
    captured within ~2 seconds of when the timestamp was captured.

    Instead of trying to read the PHC time in the Rx hotpath, the algorithm
    relies on a cached value that is periodically updated.

    Keep this cached time up to date by using the PTP .do_aux_work kthread
    function.

    The iavf_ptp_do_aux_work will reschedule itself about twice a second,
    and will check whether or not the cached PTP time needs to be updated.
    If so, it issues a VIRTCHNL_OP_1588_PTP_GET_TIME to request the time
    from the PF. The jitter and latency involved with this command aren't
    important, because the cached time just needs to be kept up to date
    within about ~2 seconds.

    Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
    Reviewed-by: Simon Horman <horms@kernel.org>
    Tested-by: Rafal Romanowski <rafal.romanowski@intel.com>
    Co-developed-by: Mateusz Polchlopek <mateusz.polchlopek@intel.com>
    Signed-off-by: Mateusz Polchlopek <mateusz.polchlopek@intel.com>
    Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

Signed-off-by: Michal Schmidt <mschmidt@redhat.com>

Author: michich

drivers/net/ethernet/intel/iavf/iavf_ptp.c

@@ -158,6 +158,56 @@ static int iavf_ptp_gettimex64(struct ptp_clock_info *info,
 	return iavf_read_phc_indirect(adapter, ts, sts);
 }
 
+/**
+ * iavf_ptp_cache_phc_time - Cache PHC time for performing timestamp extension
+ * @adapter: private adapter structure
+ *
+ * Periodically cache the PHC time in order to allow for timestamp extension.
+ * This is required because the Tx and Rx timestamps only contain 32bits of
+ * nanoseconds. Timestamp extension allows calculating the corrected 64bit
+ * timestamp. This algorithm relies on the cached time being within ~1 second
+ * of the timestamp.
+ */
+static void iavf_ptp_cache_phc_time(struct iavf_adapter *adapter)
+{
+	if (!time_is_before_jiffies(adapter->ptp.cached_phc_updated + HZ))
+		return;
+
+	/* The response from virtchnl will store the time into
+	 * cached_phc_time.
+	 */
+	iavf_send_phc_read(adapter);
+}
+
+/**
+ * iavf_ptp_do_aux_work - Perform periodic work required for PTP support
+ * @info: PTP clock info structure
+ *
+ * Handler to take care of periodic work required for PTP operation. This
+ * includes the following tasks:
+ *
+ *   1) updating cached_phc_time
+ *
+ *      cached_phc_time is used by the Tx and Rx timestamp flows in order to
+ *      perform timestamp extension, by carefully comparing the timestamp
+ *      32bit nanosecond timestamps and determining the corrected 64bit
+ *      timestamp value to report to userspace. This algorithm only works if
+ *      the cached_phc_time is within ~1 second of the Tx or Rx timestamp
+ *      event. This task periodically reads the PHC time and stores it, to
+ *      ensure that timestamp extension operates correctly.
+ *
+ * Returns: time in jiffies until the periodic task should be re-scheduled.
+ */
+static long iavf_ptp_do_aux_work(struct ptp_clock_info *info)
+{
+	struct iavf_adapter *adapter = iavf_clock_to_adapter(info);
+
+	iavf_ptp_cache_phc_time(adapter);
+
+	/* Check work about twice a second */
+	return msecs_to_jiffies(500);
+}
+
 /**
  * iavf_ptp_register_clock - Register a new PTP for userspace
  * @adapter: private adapter structure
@@ -176,6 +226,7 @@ static int iavf_ptp_register_clock(struct iavf_adapter *adapter)
 		 KBUILD_MODNAME, dev_name(dev));
 	ptp_info->owner = THIS_MODULE;
 	ptp_info->gettimex64 = iavf_ptp_gettimex64;
+	ptp_info->do_aux_work = iavf_ptp_do_aux_work;
 
 	clock = ptp_clock_register(ptp_info, dev);
 	if (IS_ERR(clock))
@@ -219,6 +270,8 @@ void iavf_ptp_init(struct iavf_adapter *adapter)
 
 		rx_ring->ptp = &adapter->ptp;
 	}
+
+	ptp_schedule_worker(adapter->ptp.clock, 0);
 }
 
 /**