i40e: only timestamp PTP event packets

The i40e_ptp_set_timestamp_mode() function is responsible for configuring
hardware timestamping. When programming receive timestamping, the logic
must determine how to configure the PRTTSYN_CTL1 register for receive
timestamping.

The i40e hardware does not support timestamping all frames. Instead,
timestamps are captured into one of the four PRTTSYN_RXTIME registers.

Currently, the driver configures hardware to timestamp all V2 packets on
ports 319 and 320, including all message types. This timestamps
significantly more packets than is actually requested by the
HWTSTAMP_FILTER_PTP_V2_EVENT filter type.

The documentation for HWTSTAMP_FILTER_PTP_V2_EVENT indicates that it should
timestamp PTP v2 messages on any layer, including any kind of event
packets.

Timestamping other packets is acceptable, but not required by the filter.
Doing so wastes valuable slots in the Rx timestamp registers. For most
applications this doesn't cause a problem. However, for extremely high
rates of messages, it becomes possible that one of the critical event
packets is not timestamped.

The PTP protocol only requires timestamps for event messages on port 319,
but hardware is timestamping on both 319 and 320, and timestamping message
types which do not need a timestamp value.

The i40e hardware actually has a more strict filtering option. First, only
timestamp layer 4 messages on port 319 instead of both 319 and 320. Second,
note that hardware has a specific mode to timestamp only event packets
(those with message type < 8).

Update the configuration to use the strict mode that only timestamps event
messages, switching the TSYNTYPE field from 10b to 11b which limits the
timestamping only to eventpackets with a Message Type of < 8. Note that the
X700 series datasheet seems to indicate that the V2MSESTYPE field is no
longer relevant. However, we only tested and validated with leaving the
V2MESSTYPE field set to 0xF for the "wildcard" behavior it documents. This
might not be required but it in that case setting it appears harmless, so
leave it as is.

This avoids wasting the valuable Rx timestamp register slots on non-event
frames, and may reduce faults when operating under high event rates.

Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Tested-by: Rinitha S <sx.rinitha@intel.com>
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://patch.msgid.link/20260430-jk-iwl-net-next-2026-04-30-v1-10-6f27ae1cd073@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

0 files changed, 0 insertions, 0 deletions