netdev - Re: [Query] ethtool cumbersome timestamping options

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Message-ID: <20250923011904.4ba598f0@kmaincent-XPS-13-7390>
Date: Tue, 23 Sep 2025 01:19:04 +0200
From: Kory Maincent <kory.maincent@...tlin.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Andrew Lunn <andrew@...n.ch>, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 netdev@...r.kernel.org, Paolo Abeni <pabeni@...hat.com>, Simon Horman
 <horms@...nel.org>
Subject: Re: [Query] ethtool cumbersome timestamping options

Hello Russell,

On Tue, 9 Sep 2025 16:40:55 +0100
"Russell King (Oracle)" <linux@...linux.org.uk> wrote:

> While spending some time with PTP stuff, specifically my Marvell PTP
> library, and getting mv88e6xxx converted to it, etc, I was trying
> out the timestamping related ethtool options:
> 
>         ethtool [ FLAGS ] -T|--show-time-stamping DEVNAME       Show time
> stamping capabilities [ index N qualifier precise|approx ]
>         ethtool [ FLAGS ] --get-hwtimestamp-cfg DEVNAME Get selected hardware
> time stamping ethtool [ FLAGS ] --set-hwtimestamp-cfg DEVNAME Select hardware
> time stamping [ index N qualifier precise|approx ]
> 
> and I'm finding them particularly cumbersome and irritating to use.
> 
> Typing:
> 
>   ethtool -T eth0 index 0 qualifier precise
> 
> or
> 
>   ethtool -T eth0 index 1 qualifier precise
> 
> is quite annoying, especially when the man page states:
> 
>            qualifier precise|approx
>                   Qualifier of the ptp hardware clock. Mainly "precise" the
> de‐ fault one is for IEEE 1588 quality and "approx" is  for  NICs
>                   DMA point.
> 
> Note "the default one". That implies if it isn't given, this is what
> will be used if it isn't specified, but this isn't so, you have to
> type the whole "qualifier precise" thing out each and every time.
> So, it isn't a default at all.
> 
> Either the man page needs to be fixed, or ethtool needs to actually
> default to the value stated in the man page.

We could indeed set the precise qualifier as default and make the option
optional. 

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