netdev - Re: [PATCH net-next RFC v4 2/5] net: Expose available time stamping layers to user space.

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Date: Fri, 12 May 2023 10:38:52 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Vladimir Oltean <vladimir.oltean@....com>
Cc: "Russell King (Oracle)" <linux@...linux.org.uk>, Andrew Lunn
 <andrew@...n.ch>, Köry Maincent
 <kory.maincent@...tlin.com>, netdev@...r.kernel.org, glipus@...il.com,
 maxime.chevallier@...tlin.com, vadim.fedorenko@...ux.dev,
 richardcochran@...il.com, gerhard@...leder-embedded.com,
 thomas.petazzoni@...tlin.com, krzysztof.kozlowski+dt@...aro.org,
 robh+dt@...nel.org
Subject: Re: [PATCH net-next RFC v4 2/5] net: Expose available time stamping
 layers to user space.

On Fri, 12 May 2023 13:29:11 +0300 Vladimir Oltean wrote:
> On Thu, May 11, 2023 at 04:16:25PM -0700, Jakub Kicinski wrote:
> > > I mean, I can't ignore the fact that there are NICs that can provide
> > > 2-step TX timestamps at line rate for all packets (not just PTP) for
> > > line rates exceeding 10G, in band with the descriptor in its TX
> > > completion queue. I don't want to give any names, just to point out
> > > that there isn't any inherent limitation in the technology.  
> > 
> > Oh, you should tell me, maybe off-list then. 'Cause I don't know any.  
> 
> I hope the examples given in private will make you reconsider the
> validity of my argument about DMA timestamps.

I may have lost track of what the argument is. There are devices
which will provide a DMA stamp for Tx and Rx. We need an API that'll
inform the user about it. 

To be clear I'm talking about drivers which are already in the tree,
not opening the door for some shoddy new HW in.