netdev - Re: [PATCH net-next v2 2/9] phy: add hwtstamp

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Message-ID: <aRXN61oICP3Vkk84@shell.armlinux.org.uk>
Date: Thu, 13 Nov 2025 12:24:11 +0000
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
Cc: Andrew Lunn <andrew+netdev@...n.ch>,
	Florian Fainelli <florian.fainelli@...adcom.com>,
	Heiner Kallweit <hkallweit1@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Andrei Botila <andrei.botila@....nxp.com>,
	Richard Cochran <richardcochran@...il.com>,
	Andrew Lunn <andrew@...n.ch>, Simon Horman <horms@...nel.org>,
	Vladimir Oltean <vladimir.oltean@....com>,
	Jacob Keller <jacob.e.keller@...el.com>,
	Kory Maincent <kory.maincent@...tlin.com>,
	bcm-kernel-feedback-list@...adcom.com, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v2 2/9] phy: add hwtstamp_get callback to phy
 drivers

On Thu, Nov 13, 2025 at 12:12:44PM +0000, Vadim Fedorenko wrote:
> On 13/11/2025 12:02, Russell King (Oracle) wrote:
> > On Thu, Nov 13, 2025 at 11:32:00AM +0000, Vadim Fedorenko wrote:
> > > PHY devices had lack of hwtstamp_get callback even though most of them
> > > are tracking configuration info. Introduce new call back to
> > > mii_timestamper.
> > > 
> > > Signed-off-by: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
> > 
> > As part of my Marvell PTP work, I have a similar patch, but it's
> > way simpler. Is this not sufficient?
> > 
> > __phy_hwtstamp_get() is called via phylib_stubs struct and
> > phy_hwtstamp_get(), dev_get_hwtstamp_phylib(), dev_get_hwtstamp(),
> > and dev_ifsioc().
> > 
> > Using the phylib ioctl handler means we're implementing a path that
> > is already marked as legacy - see dev_get_hwtstamp():
> > 
> >          if (!ops->ndo_hwtstamp_get)
> >                  return dev_eth_ioctl(dev, ifr, SIOCGHWTSTAMP); /* legacy */
> > 
> > So, I think the below would be the preferred implementation.
> 
> You mean do not add SIOCGHWTSTAMP case in phy_mii_ioctl() as we should
> never reach this legacy option?

We _can_ reach phy_mii_ioctl() for SIOCGHWTSTAMP where drivers do not
provide the ndo_hwtstamp_get() method. However, as this is legacy code,
the question is: should we add it?

> Technically, some drivers are (yet) not
> converted to ndo_hwtstamp callbacks and this part can potentially work
> for bnx2x driver, until the other series lands.

Right, but providing new features to legacy paths gives less reason for
people to stop using the legacy paths.

> I was planning to remove SIOCSHWTSTAMP/SIOCGHWTSTAMP dev_eth_ioctl calls
> later once everything has landed and we have tests confirming that ioctl
> and netlink interfaces work exactly the same way.

However, implementations that do populate non-legacy ndo_hwtstamp_get()
won't work correctly with your conversion, since we'll fall through to
the path which calls __phy_hwtstamp_get() which won't do anything.

So I disagree with your patch - it only adds support for legacy net
drivers to get the hwtstamp settings from the PHY. Non-legacy won't be
supported.

At minimum, we should be adding support for non-legacy, and _possibly_
legacy.

Let's wait for others to comment on my point about adding this for the
legacy drivers/code path.

-- 
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