sfc: Tidy up PTP synchronization code

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

1 files changed, 24 insertions, 20 deletions

diff --git a/drivers/net/ethernet/sfc/ptp.c b/drivers/net/ethernet/sfc/ptp.c
index 82d8e27e8a58..361d7cedd897 100644
--- a/drivers/net/ethernet/sfc/ptp.c
+++ b/drivers/net/ethernet/sfc/ptp.c
@@ -435,7 +435,6 @@ efx_ptp_process_times(struct efx_nic *efx, MCDI_DECLARE_STRUCT_PTR(synch_buf),
                 MCDI_VAR_ARRAY_LEN(response_length,
                                    PTP_OUT_SYNCHRONIZE_TIMESET);
         unsigned i;
-        unsigned total;
         unsigned ngood = 0;
         unsigned last_good = 0;
         struct efx_ptp_data *ptp = efx->ptp_data;
@@ -446,33 +445,38 @@ efx_ptp_process_times(struct efx_nic *efx, MCDI_DECLARE_STRUCT_PTR(synch_buf),
         if (number_readings == 0)
                 return -EAGAIN;
 
-        /* Read the set of results and increment stats for any results that
-         * appera to be erroneous.
+        /* Read the set of results and find the last good host-MC
+         * synchronization result. The MC times when it finishes reading the
+         * host time so the corrected window time should be fairly constant
+         * for a given platform.
          */
         for (i = 0; i < number_readings; i++) {
+                s32 window, corrected;
+
                 efx_ptp_read_timeset(
                         MCDI_ARRAY_STRUCT_PTR(synch_buf,
                                               PTP_OUT_SYNCHRONIZE_TIMESET, i),
                         &ptp->timeset[i]);
-        }
 
-        /* Find the last good host-MC synchronization result. The MC times
-         * when it finishes reading the host time so the corrected window time
-         * should be fairly constant for a given platform.
-         */
-        total = 0;
-        for (i = 0; i < number_readings; i++)
-                if (ptp->timeset[i].window > ptp->timeset[i].waitns) {
-                        unsigned win;
-
-                        win = ptp->timeset[i].window - ptp->timeset[i].waitns;
-                        if (win >= MIN_SYNCHRONISATION_NS &&
-                            win < MAX_SYNCHRONISATION_NS) {
-                                total += ptp->timeset[i].window;
-                                ngood++;
-                                last_good = i;
-                        }
+                window = ptp->timeset[i].window;
+                corrected = window - ptp->timeset[i].waitns;
+
+                /* We expect the uncorrected synchronization window to be at
+                 * least as large as the interval between host start and end
+                 * times. If it is smaller than this then this is mostly likely
+                 * to be a consequence of the host's time being adjusted.
+                 * Check that the corrected sync window is in a reasonable
+                 * range. If it is out of range it is likely to be because an
+                 * interrupt or other delay occurred between reading the system
+                 * time and writing it to MC memory.
+                 */
+                if (window >= SYNCHRONISATION_GRANULARITY_NS &&
+                    corrected < MAX_SYNCHRONISATION_NS &&
+                    corrected >= MIN_SYNCHRONISATION_NS) {
+                        ngood++;
+                        last_good = i;
                 }
+        }
 
         if (ngood == 0) {
                 netif_warn(efx, drv, efx->net_dev,