Messages in this thread |  | | Date | Tue, 5 May 2026 10:08:26 +0200 | | Subject | Re: [PATCH net-next v5 3/3] gve: implement PTP gettimex64 | | From | Paolo Abeni <> |
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On 4/29/26 3:28 AM, Harshitha Ramamurthy wrote: > From: Jordan Rhee <jordanrhee@google.com> > > Enable chrony and phc2sys to synchronize system clock to NIC clock. > > The system cycle counters are sampled by the device to minimize the > uncertainty window. If the system times are sampled in the host, the > delta between pre and post readings is 100us or more due to AQ command > latency. The system times returned by the device have a delta of ~1us, > which enables significantly more accurate clock synchronization. > > Reviewed-by: Willem de Bruijn <willemb@google.com> > Reviewed-by: Kevin Yang <yyd@google.com> > Reviewed-by: Naman Gulati <namangulati@google.com> > Signed-off-by: Jordan Rhee <jordanrhee@google.com> > Signed-off-by: Harshitha Ramamurthy <hramamurthy@google.com> > --- > Changes in v5: > - Reformulate retry loop in terms of total timeout (Jakub Kicinski) > > Changes in v3: > - Take system time snapshot inside the mutex > - Return -EOPNOTSUPP if cross-timestamp is requested on an arch other > than x86 or arm64 > > Changes in v2: > - fix compilation warning on ARM by casting cycles_t to u64 > --- > drivers/net/ethernet/google/gve/gve_adminq.h | 4 +- > drivers/net/ethernet/google/gve/gve_ptp.c | 196 ++++++++++++++++++- > 2 files changed, 191 insertions(+), 9 deletions(-) > > diff --git a/drivers/net/ethernet/google/gve/gve_adminq.h b/drivers/net/ethernet/google/gve/gve_adminq.h > index 22a74b6aa17e..e6dcf6da9091 100644 > --- a/drivers/net/ethernet/google/gve/gve_adminq.h > +++ b/drivers/net/ethernet/google/gve/gve_adminq.h > @@ -411,8 +411,8 @@ static_assert(sizeof(struct gve_adminq_report_nic_ts) == 16); > > struct gve_nic_ts_report { > __be64 nic_timestamp; /* NIC clock in nanoseconds */ > - __be64 reserved1; > - __be64 reserved2; > + __be64 pre_cycles; /* System cycle counter before NIC clock read */ > + __be64 post_cycles; /* System cycle counter after NIC clock read */ > __be64 reserved3; > __be64 reserved4; > }; > diff --git a/drivers/net/ethernet/google/gve/gve_ptp.c b/drivers/net/ethernet/google/gve/gve_ptp.c > index ad15f1209a83..c6c98ef825aa 100644 > --- a/drivers/net/ethernet/google/gve/gve_ptp.c > +++ b/drivers/net/ethernet/google/gve/gve_ptp.c > @@ -10,28 +10,210 @@ > /* Interval to schedule a nic timestamp calibration, 250ms. */ > #define GVE_NIC_TS_SYNC_INTERVAL_MS 250 > > +/* > + * Stores cycle counter samples in get_cycles() units from a > + * sandwiched NIC clock read > + */ > +struct gve_sysclock_sample { > + /* system time snapshot taken just before issuing AdminQ command */ > + struct system_time_snapshot snapshot; > + /* Cycle counter from NIC before clock read */ > + u64 nic_pre_cycles; > + /* Cycle counter from NIC after clock read */ > + u64 nic_post_cycles; > + /* Cycle counter from host before issuing AQ command */ > + cycles_t host_pre_cycles; > + /* Cycle counter from host after AQ command returns */ > + cycles_t host_post_cycles; > +}; > + > +/* > + * Read NIC clock by issuing the AQ command. The command is subject to > + * rate limiting and may need to be retried. Requires nic_ts_read_lock > + * to be held. > + */ > +static int gve_ptp_read_timestamp(struct gve_ptp *ptp, cycles_t *pre_cycles, > + cycles_t *post_cycles, > + struct system_time_snapshot *snap) > +{ > + unsigned long deadline = jiffies + msecs_to_jiffies(100); > + unsigned long delay_us = 1000; > + int err; > + > + lockdep_assert_held(&ptp->nic_ts_read_lock); > + > + do { > + if (snap) > + ktime_get_snapshot(snap); > + > + *pre_cycles = get_cycles(); > + err = gve_adminq_report_nic_ts(ptp->priv, > + ptp->nic_ts_report_bus); > + > + /* Prevent get_cycles() from being speculatively executed > + * before the AdminQ command > + */ > + rmb(); > + *post_cycles = get_cycles(); > + if (likely(err != -EAGAIN)) > + return err; > + > + fsleep(delay_us); > + > + /* Exponential backoff */ > + delay_us *= 2; > + } while (time_before(jiffies, deadline)); > + > + return -ETIMEDOUT; > +} > + > /* Read the nic timestamp from hardware via the admin queue. */ > -static int gve_clock_nic_ts_read(struct gve_ptp *ptp, u64 *nic_raw) > +static int gve_clock_nic_ts_read(struct gve_ptp *ptp, u64 *nic_raw, > + struct gve_sysclock_sample *sysclock) > { > + cycles_t host_pre_cycles, host_post_cycles; > + struct gve_nic_ts_report *ts_report; > int err; > > mutex_lock(&ptp->nic_ts_read_lock); > - err = gve_adminq_report_nic_ts(ptp->priv, ptp->nic_ts_report_bus); > - if (err) > + err = gve_ptp_read_timestamp(ptp, &host_pre_cycles, &host_post_cycles, > + sysclock ? &sysclock->snapshot : NULL); > + if (err) { > + dev_err_ratelimited(&ptp->priv->pdev->dev, > + "AdminQ timestamp read failed: %d\n", err); > goto out; > + } > > - *nic_raw = be64_to_cpu(ptp->nic_ts_report->nic_timestamp); > + ts_report = ptp->nic_ts_report; > + *nic_raw = be64_to_cpu(ts_report->nic_timestamp); > + > + if (sysclock) { > + sysclock->nic_pre_cycles = be64_to_cpu(ts_report->pre_cycles); > + sysclock->nic_post_cycles = be64_to_cpu(ts_report->post_cycles); > + sysclock->host_pre_cycles = host_pre_cycles; > + sysclock->host_post_cycles = host_post_cycles; > + } > > out: > mutex_unlock(&ptp->nic_ts_read_lock); > return err; > } > > +struct gve_cycles_to_clock_callback_ctx { > + u64 cycles; > +}; > + > +static int gve_cycles_to_clock_fn(ktime_t *device_time, > + struct system_counterval_t *system_counterval, > + void *ctx) > +{ > + struct gve_cycles_to_clock_callback_ctx *context = ctx; > + > + *device_time = 0; > + > + system_counterval->cycles = context->cycles; > + system_counterval->use_nsecs = false; > + > + if (IS_ENABLED(CONFIG_X86)) > + system_counterval->cs_id = CSID_X86_TSC; > + else if (IS_ENABLED(CONFIG_ARM64)) > + system_counterval->cs_id = CSID_ARM_ARCH_COUNTER; > + else > + return -EOPNOTSUPP; > + > + return 0; > +} > + > +/* > + * Convert a raw cycle count (e.g. from get_cycles()) to the system clock > + * type specified by clockid. The system_time_snapshot must be taken before > + * the cycle counter is sampled. > + */ > +static int gve_cycles_to_timespec64(struct gve_priv *priv, clockid_t clockid, > + struct system_time_snapshot *snap, > + u64 cycles, struct timespec64 *ts) > +{ > + struct gve_cycles_to_clock_callback_ctx ctx = {0}; > + struct system_device_crosststamp xtstamp; > + int err; > + > + ctx.cycles = cycles; > + err = get_device_system_crosststamp(gve_cycles_to_clock_fn, &ctx, snap, > + &xtstamp); > + if (err) { > + dev_err_ratelimited(&priv->pdev->dev, > + "get_device_system_crosststamp() failed to convert %lld cycles to system time: %d\n", > + cycles, > + err); > + return err; > + } > + > + switch (clockid) { > + case CLOCK_REALTIME: > + *ts = ktime_to_timespec64(xtstamp.sys_realtime); > + break; > + case CLOCK_MONOTONIC_RAW: > + *ts = ktime_to_timespec64(xtstamp.sys_monoraw); > + break; > + default: > + dev_err_ratelimited(&priv->pdev->dev, > + "Cycle count conversion to clockid %d not supported\n", > + clockid); > + return -EOPNOTSUPP; > + } > + > + return 0; > +} > + > static int gve_ptp_gettimex64(struct ptp_clock_info *info, > struct timespec64 *ts, > struct ptp_system_timestamp *sts) > { > - return -EOPNOTSUPP; > + struct gve_ptp *ptp = container_of(info, struct gve_ptp, info); > + struct gve_sysclock_sample sysclock = {0}; > + struct gve_priv *priv = ptp->priv; > + u64 nic_ts; > + int err; > + > + if (sts && !(IS_ENABLED(CONFIG_X86) || IS_ENABLED(CONFIG_ARM64))) > + return -EOPNOTSUPP; > + > + err = gve_clock_nic_ts_read(ptp, &nic_ts, sts ? &sysclock : NULL); > + if (err) > + return err; > + > + if (sts) { > + /* Reject samples with out of order system clock values */ > + if (!(sysclock.host_pre_cycles <= sysclock.nic_pre_cycles && > + sysclock.nic_pre_cycles <= sysclock.nic_post_cycles && > + sysclock.nic_post_cycles <= sysclock.host_post_cycles)) { > + dev_err_ratelimited(&priv->pdev->dev, > + "AdminQ system clock cycle counts out of order. Expecting %llu <= %llu <= %llu <= %llu\n", > + (u64)sysclock.host_pre_cycles, > + sysclock.nic_pre_cycles, > + sysclock.nic_post_cycles, > + (u64)sysclock.host_post_cycles); > + return -EBADMSG;
Sashiko/gemini is reporting the following:
--- If older firmware does not support this feature and returns 0 for the pre_cycles and post_cycles fields, won't host_pre_cycles <= nic_pre_cycles evaluate to false since get_cycles() will be greater than 0? If this occurs, the driver returns -EBADMSG instead of -EOPNOTSUPP. Does returning -EBADMSG prevent userspace tools from gracefully falling back to legacy PTP ioctls like PTP_SYS_OFFSET, causing PTP synchronization to fail completely on older firmwares? ---
which looks legit to me, or am I missing something? Note that proactively triaging sashiko comments would help maintainers a lot.
Thanks,
Paolo
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