netdev - Re: [PATCH RFC net-next 1/5] net: mvpp2: add support for hardware timestamps

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Message-ID: <20250414145150.63b29770@kmaincent-XPS-13-7390>
Date: Mon, 14 Apr 2025 14:51:50 +0200
From: Kory Maincent <kory.maincent@...tlin.com>
To: Russell King <rmk+kernel@...linux.org.uk>
Cc: Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>,
 Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski
 <kuba@...nel.org>, Marcin Wojtas <marcin.s.wojtas@...il.com>,
 netdev@...r.kernel.org, Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH RFC net-next 1/5] net: mvpp2: add support for hardware
 timestamps

On Fri, 11 Apr 2025 22:26:31 +0100
Russell King <rmk+kernel@...linux.org.uk> wrote:

> Add support for hardware timestamps in (e.g.) the PHY by calling
> skb_tx_timestamp() as close as reasonably possible to the point that
> the hardware is instructed to send the queued packets.
> 
> Signed-off-by: Russell King <rmk+kernel@...linux.org.uk>

Reviewed-by: Kory Maincent <kory.maincent@...tlin.com>

> ---
>  drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
> b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c index
> 416a926a8281..e3f8aa139d1e 100644 ---
> a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c +++
> b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c @@ -4439,6 +4439,8 @@
> static netdev_tx_t mvpp2_tx(struct sk_buff *skb, struct net_device *dev)
> txq_pcpu->count += frags; aggr_txq->count += frags;
>  
> +		skb_tx_timestamp(skb);
> +
>  		/* Enable transmit */
>  		wmb();
>  		mvpp2_aggr_txq_pend_desc_add(port, frags);

Small question for my curiosity here. Shouldn't we move the skb_tx_timestamp()
call after the memory barrier for a better precision or is it negligible?

Regards,
-- 
Köry Maincent, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com