> From: Patel, Vedang
> Sent: Tuesday, June 25, 2019 3:07 PM
> To: netdev@vger.kernel.org
> Cc: Kirsher, Jeffrey T <jeffrey.t.kirs...@intel.com>; da...@davemloft.net;
> j...@mojatatu.com; xiyou.wangc...@gmail.com; j...@resnulli.us; intel-wired-
> l...@lists.osuosl.org; Gomes, Vinicius <vinicius.go...@intel.com>;
> l...@dorileo.org; jakub.kicin...@netronome.com; m-kariche...@ti.com;
> sergei.shtyl...@cogentembedded.com; eric.duma...@gmail.com; Brown,
> Aaron F <aaron.f.br...@intel.com>; Patel, Vedang <vedang.pa...@intel.com>
> Subject: [PATCH net-next v6 1/8] igb: clear out skb->tstamp after reading the
> txtime
>
> If a packet which is utilizing the launchtime feature (via SO_TXTIME socket
> option) also requests the hardware transmit timestamp, the hardware
> timestamp is not delivered to the userspace. This is because the value in
> skb->tstamp is mistaken as the software timestamp.
>
> Applications, like ptp4l, request a hardware timestamp by setting the
> SOF_TIMESTAMPING_TX_HARDWARE socket option. Whenever a new
> timestamp is
> detected by the driver (this work is done in igb_ptp_tx_work() which calls
> igb_ptp_tx_hwtstamps() in igb_ptp.c[1]), it will queue the timestamp in the
> ERR_QUEUE for the userspace to read. When the userspace is ready, it will
> issue a recvmsg() call to collect this timestamp. The problem is in this
> recvmsg() call. If the skb->tstamp is not cleared out, it will be
> interpreted as a software timestamp and the hardware tx timestamp will not
> be successfully sent to the userspace. Look at skb_is_swtx_tstamp() and the
> callee function __sock_recv_timestamp() in net/socket.c for more details.
>
> Signed-off-by: Vedang Patel <vedang.pa...@intel.com>
> ---
> drivers/net/ethernet/intel/igb/igb_main.c | 1 +
> 1 file changed, 1 insertion(+)
>
Tested-by: Aaron Brown <aaron.f.br...@intel.com>
