netdev - Re: [PATCH net-next RFC v4 4/5] net: Let the active time stamping layer be selectable.

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Date: Thu, 11 May 2023 16:35:47 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Vladimir Oltean <vladimir.oltean@....com>
Cc: 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,
 linux@...linux.org.uk
Subject: Re: [PATCH net-next RFC v4 4/5] net: Let the active time stamping
 layer be selectable.

On Fri, 12 May 2023 02:18:03 +0300 Vladimir Oltean wrote:
> > Why can't we treat ndo_hwtstamp_set() == -EOPNOTSUPP as a signal 
> > to call the PHY? ndo_hwtstamp_set() does not exist, we can give
> > it whatever semantics we want.  
> 
> Hmm, because if we do that, bridged DSA switch ports without hardware
> timestamping support and without logic to trap PTP to the CPU will just
> spew those PTP frames with PHY hardware timestamps everywhere, instead
> of just telling the user hey, the configuration isn't supported?

I see, so there is a legit reason to abort. 

We could use one of the high error codes, then, to signal 
the "I didn't care, please carry on to the PHY" condition?
-ENOTSUPP?

I guess we can add a separate "please configure traps for PTP/NTP" 
NDO, if you prefer. Mostly an implementation detail.