netdev - Re: [PATCH net-next v4 4/6] ptp: Support late timestamp determination

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Message-ID: <20220506230234.ig3qru6qbqxgfvjm@bsd-mbp.dhcp.thefacebook.com>
Date:   Fri, 6 May 2022 16:02:34 -0700
From:   Jonathan Lemon <jonathan.lemon@...il.com>
To:     Gerhard Engleder <gerhard@...leder-embedded.com>
Cc:     richardcochran@...il.com, vinicius.gomes@...el.com,
        yangbo.lu@....com, davem@...emloft.net, kuba@...nel.org,
        mlichvar@...hat.com, willemb@...gle.com, kafai@...com,
        netdev@...r.kernel.org
Subject: Re: [PATCH net-next v4 4/6] ptp: Support late timestamp determination

On Fri, May 06, 2022 at 10:01:40PM +0200, Gerhard Engleder wrote:
> If a physical clock supports a free running cycle counter, then
> timestamps shall be based on this time too. For TX it is known in
> advance before the transmission if a timestamp based on the free running
> cycle counter is needed. For RX it is impossible to know which timestamp
> is needed before the packet is received and assigned to a socket.
> 
> Support late timestamp determination by a network device. Therefore, an
> address/cookie is stored within the new netdev_data field of struct
> skb_shared_hwtstamps. This address/cookie is provided to a new network
> device function called ndo_get_tstamp(), which returns a timestamp based
> on the normal/adjustable time or based on the free running cycle
> counter. If function is not supported, then timestamp handling is not
> changed.
> 
> This mechanism is intended for RX, but TX use is also possible.
> 
> Signed-off-by: Gerhard Engleder <gerhard@...leder-embedded.com>

Acked-by: Jonathan Lemon <jonathan.lemon@...il.com>