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

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Message-ID: <20230522132144.018b375b@kernel.org>
Date: Mon, 22 May 2023 13:21:44 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Richard Cochran <richardcochran@...il.com>
Cc: "Zulkifli, Muhammad Husaini" <muhammad.husaini.zulkifli@...el.com>,
 Vladimir Oltean <vladimir.oltean@....com>, "Russell King (Oracle)"
 <linux@...linux.org.uk>, Andrew Lunn <andrew@...n.ch>, Köry
 Maincent <kory.maincent@...tlin.com>, "netdev@...r.kernel.org"
 <netdev@...r.kernel.org>, "glipus@...il.com" <glipus@...il.com>,
 "maxime.chevallier@...tlin.com" <maxime.chevallier@...tlin.com>,
 "vadim.fedorenko@...ux.dev" <vadim.fedorenko@...ux.dev>,
 "gerhard@...leder-embedded.com" <gerhard@...leder-embedded.com>,
 "thomas.petazzoni@...tlin.com" <thomas.petazzoni@...tlin.com>,
 "krzysztof.kozlowski+dt@...aro.org" <krzysztof.kozlowski+dt@...aro.org>,
 "robh+dt@...nel.org" <robh+dt@...nel.org>, "Keller, Jacob E"
 <jacob.e.keller@...el.com>
Subject: Re: [PATCH net-next RFC v4 2/5] net: Expose available time stamping
 layers to user space.

On Mon, 22 May 2023 13:04:33 -0700 Richard Cochran wrote:
> On Mon, May 22, 2023 at 03:56:36AM +0000, Zulkifli, Muhammad Husaini wrote:
> 
> > A controller may only support one HW Timestamp (PHY/Port) and one MAC Timestamp 
> > (DMA Timestamp) for packet timestamp activity. If a PTP packet has used the HW Timestamp (PHY/Port),   
> 
> This is wrong.
>
> The time stamping setting is global, at the device level, not at the
> socket.  And that is not going to change.  This series is about
> selecting between MAC/PHY time stamping globally, at the device level.

What constitutes a device?

I'd present the facts differently. This series selects which _device_
(MAC or PHY) is responsible for delivering timestamps for a given
netdev.

HW which supports different timestamping points with different
capabilities is commonplace, so an API in this vicinity should be
extended to support the configuration. Today it's configured via device
private flags, or some out-of-tree tooling, which helps nobody :|