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Date: Wed, 10 Apr 2024 06:19:28 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: Rahul Rameshbabu <rrameshbabu@nvidia.com>
Cc: Willem de Bruijn <willemdebruijn.kernel@gmail.com>, John Fraker
 <jfraker@google.com>, netdev@vger.kernel.org, Praveen  Kaligineedi
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 <jeroendb@google.com>, linux-kernel@vger.kernel.org,
 kory.maincent@bootlin.com, andrew@lunn.ch, richardcochran@gmail.com
Subject: Re: [PATCH net-next] gve: Correctly report software timestamping
 capabilities
Message-ID: <20240410061928.712ff9a3@kernel.org>
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On Tue, 09 Apr 2024 21:40:46 -0700 Rahul Rameshbabu wrote:
> > My gut tells me we force drivers to set the ethtool op because
> > while at it they will probably also implement tx stamping.  
> 
> I think the logic should be the other way (in terms of the
> relationship). A call to skb_tx_timestamp should throw a warning if the
> driver does not advertise its timestamping capabilities. This way, a
> naive netdev driver for some lightweight device does not need to worry
> about this. I agree that anyone implementing tx timestamping should have
> this operation defined. An skb does not contain any mechanism to
> reference the driver's ethtool callback. Maybe the right choice is to
> have a ts capability function registered for each netdev that can be
> used by the core stack and that powers the ethtool operation as well
> instead of the existing callback for ethtool?

Adding a check which only need to runs once in the lifetime of
the driver to the fastpath may be a little awkward. Another option
would be a sufficiently intelligent grep, which would understand
which files constitute a driver. At which point grepping for 
the ethtool op and skb_tx_timestamp would be trivial?