On Sun, Nov 06, 2016 at 07:30:48PM +0100, Jan Deinhard wrote:
> $ ethtool -T eth0
> Time stamping parameters for eth0:
> Capabilities:
> software-receive (SOF_TIMESTAMPING_RX_SOFTWARE)
> software-system-clock (SOF_TIMESTAMPING_SOFTWARE)
You are missing:
software-transmit (SOF_TIMESTAMPING_TX_SOFTWARE)
> What is the difference between options -S and -H?
-S gets the time stamps in software in the Linux networking stack.
> What hardware support is needed for option -S?
No special HW support is needed.
> Is it a driver problem?
Yes. The receive time stamp is handled by the core networking code,
but the transmit time stamp must be done in the driver. Many, but not
all drivers implement it.
You need to add one line to the transmit path in the driver:
skb_tx_timestamp(skb);
Quoting include/linux/skbuff.h:
* skb_tx_timestamp() - Driver hook for transmit timestamping
*
* Ethernet MAC Drivers should call this function in their hard_xmit()
* function immediately before giving the sk_buff to the MAC hardware.
*
* Specifically, one should make absolutely sure that this function is
* called before TX completion of this packet can trigger. Otherwise
* the packet could potentially already be freed.
HTH,
Richard
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