Re: [PATCH net-next 6/7] net: dsa: netc: add PTP two-step timestamping support

[Vadim Fedorenko <vadim.fedorenko@linux.dev>]

On 28/07/2026 11:45, wei.fang@oss.nxp.com wrote:
> From: Wei Fang <wei.fang@nxp.com>
> 
> Add two-step TX timestamping and RX timestamping for the NETC switch.
> One-step TX timestamping is not supported yet.
> 
> For RX, install ingress port filter table (IPFT) rules that redirect PTP
> frames to the CPU port. Support L2, L4 over IPv4 and L4 over IPv6, for
> both event and general messages, selected via the hwtstamp rx_filter.
> The hardware prepends a To_Host subtype 1 tag carrying the 64-bit ingress
> timestamp. The tagger extracts it into the skb control buffer, and
> netc_port_rxtstamp() copies it into skb_hwtstamps().
> 
> For two-step TX, clone the skb and allocate a 4-bit timestamp request ID,
> then queue the clone on a per-port list. netc_xmit() emits a To_Port
> subtype 2 tag carrying that ID. The hardware echoes the ID back in a
> generated To_Host subtype 2 response frame together with the 64-bit
> transmit timestamp. The tagger dispatches the ID and timestamp to the
> switch driver through the twostep_tstamp_handler callback registered in
> netc_tagger_data, which matches the queued clone and completes it via
> skb_complete_tx_timestamp(), then frees the response skb. Non-PTP frames
> keep using the To_Port subtype 0 tag on the xmit fast path.
> 
> The two-step response frame carries no payload; its total length is only
> 26 bytes (12 bytes of DMAC and SMAC plus a 14-byte switch tag). By the
> time netc_rcv() sees it, skb->data already points 2 bytes into the switch
> tag, past the TPID shared with the Ethernet header, so skb->len is only
> 12. Since the tag pointer is at (skb->data - 2), the pskb_may_pull() check
> must use NETC_TAG_MAX_LEN - 2 rather than NETC_TAG_MAX_LEN. Otherwise
> pskb_may_pull() drops the response frame and breaks PTP synchronization.
> 
> Add the To_Port subtype 2 and To_Host subtype 1/2 tag structures, extend
> netc_xmit() to select the tag based on ptp_flag in the skb control buffer,
> and add netc_connect()/netc_disconnect() to manage the per-switch
> netc_tagger_data allocation. Grab the PTP timer's pci_dev in netc_setup()
> so get_ts_info() can report its PHC index, and release it in the teardown
> and error paths.
> 
> Signed-off-by: Wei Fang <wei.fang@nxp.com>
> ---
>   drivers/net/dsa/netc/Kconfig         |   1 +
>   drivers/net/dsa/netc/Makefile        |   3 +-
>   drivers/net/dsa/netc/netc_main.c     |  72 +++++
>   drivers/net/dsa/netc/netc_platform.c |   1 +
>   drivers/net/dsa/netc/netc_ptp.c      | 411 +++++++++++++++++++++++++++
>   drivers/net/dsa/netc/netc_switch.h   |  35 +++
>   include/linux/dsa/tag_netc.h         |  23 ++
>   net/dsa/tag_netc.c                   | 120 +++++++-
>   8 files changed, 658 insertions(+), 8 deletions(-)
>   create mode 100644 drivers/net/dsa/netc/netc_ptp.c

[...]

> +int netc_get_ts_info(struct dsa_switch *ds, int port,
> +		     struct kernel_ethtool_ts_info *info)
> +{
> +	struct netc_switch *priv = ds->priv;
> +
> +	info->so_timestamping = SOF_TIMESTAMPING_TX_SOFTWARE |
> +				SOF_TIMESTAMPING_RX_SOFTWARE |
> +				SOF_TIMESTAMPING_SOFTWARE;

SOF_TIMESTAMPING_RX_SOFTWARE and SOF_TIMESTAMPING_SOFTWARE are available 
by default, no need to add them.

the code doesn't have skb_tx_timestamp() calls, I wonder how is
SOF_TIMESTAMPING_TX_SOFTWARE implemented?

> +
> +	info->phc_index = netc_get_phc_index(priv);
> +	if (info->phc_index < 0)
> +		return 0;
> +
> +	info->so_timestamping |= SOF_TIMESTAMPING_TX_HARDWARE |
> +				 SOF_TIMESTAMPING_RX_HARDWARE |
> +				 SOF_TIMESTAMPING_RAW_HARDWARE;
> +
> +	info->tx_types = BIT(HWTSTAMP_TX_OFF) | BIT(HWTSTAMP_TX_ON);
> +
> +	info->rx_filters = BIT(HWTSTAMP_FILTER_NONE) |
> +			   BIT(HWTSTAMP_FILTER_PTP_V2_EVENT) |
> +			   BIT(HWTSTAMP_FILTER_PTP_V2_L2_EVENT) |
> +			   BIT(HWTSTAMP_FILTER_PTP_V2_L4_EVENT);
> +
> +	return 0;
> +}