On Thu, 18 Apr, 2024 01:24:56 -0400 Mateusz Polchlopek
<mateusz.polchlo...@intel.com> wrote:
> From: Jacob Keller <jacob.e.kel...@intel.com>
>
> 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.
Seems reasonable.
>
> 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.
>
> Reviewed-by: Wojciech Drewek <wojciech.dre...@intel.com>
> Signed-off-by: Jacob Keller <jacob.e.kel...@intel.com>
> Co-developed-by: Mateusz Polchlopek <mateusz.polchlo...@intel.com>
> Signed-off-by: Mateusz Polchlopek <mateusz.polchlo...@intel.com>
> ---
> drivers/net/ethernet/intel/iavf/iavf_ptp.c | 52 ++++++++++++++++++++++
> drivers/net/ethernet/intel/iavf/iavf_ptp.h | 1 +
> 2 files changed, 53 insertions(+)
>
> diff --git a/drivers/net/ethernet/intel/iavf/iavf_ptp.c
> b/drivers/net/ethernet/intel/iavf/iavf_ptp.c
<snip>
> +/**
> + * iavf_ptp_do_aux_work - Perform periodic work required for PTP support
> + * @ptp: 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.
> + */
> +long iavf_ptp_do_aux_work(struct ptp_clock_info *ptp)
> +{
> + struct iavf_adapter *adapter = clock_to_adapter(ptp);
> +
> + iavf_ptp_cache_phc_time(adapter);
> +
> + /* Check work about twice a second */
> + return msecs_to_jiffies(500);
HZ / 2 might be more intuitive?
> +}
> +
<snip>
