[Intel-wired-lan] [PATCH iwl-next v12 08/14] iavf: periodically cache PHC time

[Romanowski, Rafal]

> -----Original Message-----
> From: Intel-wired-lan <intel-wired-lan-bounces at osuosl.org> On Behalf Of
> Mateusz Polchlopek
> Sent: Tuesday, October 22, 2024 1:41 PM
> To: intel-wired-lan at lists.osuosl.org
> Cc: netdev at vger.kernel.org; Keller, Jacob E <jacob.e.keller at intel.com>; Drewek,
> Wojciech <wojciech.drewek at intel.com>; Simon Horman <horms at kernel.org>;
> Polchlopek, Mateusz <mateusz.polchlopek at intel.com>
> Subject: [Intel-wired-lan] [PATCH iwl-next v12 08/14] iavf: periodically cache PHC
> time
> 
> From: Jacob Keller <jacob.e.keller at 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.
> 
> 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 at intel.com>
> Reviewed-by: Wojciech Drewek <wojciech.drewek at intel.com>
> Reviewed-by: Simon Horman <horms at kernel.org>
> Co-developed-by: Mateusz Polchlopek <mateusz.polchlopek at intel.com>
> Signed-off-by: Mateusz Polchlopek <mateusz.polchlopek at intel.com>
> ---


Tested-by: Rafal Romanowski <rafal.romanowski at intel.com>