Re: [PATCH net v2] net: ethernet: ti: am65-cpts: keep port and direction when matching PTPv1 TX timestamps

[Simon Horman <horms@kernel.org>]

On Tue, Nov 03, 2026 at 09:42:52AM +0100, Jesper L. Nielsen wrote:
> The CPTS reports the message type of a timestamp event using the PTPv2
> header layout, i.e. the low nibble of the first header byte. In a PTPv1
> header that byte is the upper byte of versionPTP and always 0, so every
> PTPv1 event is reported as message type 0, while
> am65_skb_get_mtype_seqid() reads the PTPv1 message type from the control
> field. To make PTPv1 match at all, commit 1b9e743e923b ("net: ethernet:
> ti: am65-cpts: Fix PTPv1 message type on TX packets") overwrites the
> whole value compared against the skb with the skb's own value once the
> sequence ids are equal. That throws away the event type and the port
> number of the event as well, so a PTPv1 skb matches any TX event with
> the same sequence id on either port. For PTPv1 this defeats
> commit a23c657e332f ("net: ethernet: ti: am65-cpsw: Use also port
> number to identify timestamps"). The overwritten value also sticks for
> the rest of the TX queue walk.
> 
> Since every PTPv1 frame reads as message type 0, the hardware timestamps
> all PTPv1 frames to UDP ports 319 and 320, including Follow_Up and
> Delay_Resp, for which no skb waits. With a PTPv1 master on both ports
> whose sequence ids run in step (e.g. a Dante device with primary and
> secondary network started at the same time), the unclaimed TX event of
> Follow_Up N on one port is still on the event list when the other port
> queues Sync N, and am65_cpts_find_tx_ts() tries to match before it
> checks for expiry. Sync N then gets the transmit time of the other
> port's Follow_Up N, and the master announces a preciseOriginTimestamp up
> to one Sync interval early to every slave on that network.
> 
> For PTPv1 replace only the message type of the event with the skb's and
> keep its event type, port number and sequence id, and compute the value
> per skb.
> 
> Tested on AM62x with ti-linux-6.12.y and the port number commit backported:
> without this patch every boot in which both ports started PTP together
> (10 of 10) sent wrong Sync timestamps, with it none did (0 of 29).
> 
> The bug was tracked down, and this fix and changelog drafted, with the
> help of an AI coding assistant (Claude). I reviewed and tested it on
> hardware as described above.
> 
> Fixes: a23c657e332f ("net: ethernet: ti: am65-cpsw: Use also port number to identify timestamps")
> Signed-off-by: Jesper L. Nielsen <jln@pascal-audio.com>
> Reviewed-by: Siddharth Vadapalli <s-vadapalli@ti.com>
> ---
> Changes in v2:
> - Wrap the commit a23c657e332f reference like the one above it (Siddharth)
> - Use netdev comment style for the new comment (Siddharth)
> - Collect Reviewed-by from Siddharth
> - Link to v1: https://patch.msgid.link/20261030-am65-cpts-ptpv1-v1-1-0bb4c370d970@pascal-audio.com

Reviewed-by: Simon Horman <horms@kernel.org>