linux-kernel - Re: [PATCH v8 net-next 12/12] net: remove phy_has_hwtstamp() -> phy_mii

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Date:   Tue, 18 Jul 2023 17:46:52 +0300
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Maxim Georgiev <glipus@...il.com>,
        Horatiu Vultur <horatiu.vultur@...rochip.com>,
        Köry Maincent <kory.maincent@...tlin.com>,
        Maxime Chevallier <maxime.chevallier@...tlin.com>,
        Richard Cochran <richardcochran@...il.com>,
        Vadim Fedorenko <vadim.fedorenko@...ux.dev>,
        Gerhard Engleder <gerhard@...leder-embedded.com>,
        Hangbin Liu <liuhangbin@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Jacob Keller <jacob.e.keller@...el.com>,
        Jay Vosburgh <j.vosburgh@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>,
        Wei Fang <wei.fang@....com>,
        Shenwei Wang <shenwei.wang@....com>,
        Clark Wang <xiaoning.wang@....com>,
        NXP Linux Team <linux-imx@....com>,
        UNGLinuxDriver@...rochip.com,
        Lars Povlsen <lars.povlsen@...rochip.com>,
        Steen Hegelund <Steen.Hegelund@...rochip.com>,
        Daniel Machon <daniel.machon@...rochip.com>,
        Simon Horman <simon.horman@...igine.com>,
        Casper Andersson <casper.casan@...il.com>,
        Sergey Organov <sorganov@...il.com>,
        Michal Kubecek <mkubecek@...e.cz>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 net-next 12/12] net: remove phy_has_hwtstamp() ->
 phy_mii_ioctl() decision from converted drivers

On Tue, Jul 18, 2023 at 03:38:27PM +0100, Russell King (Oracle) wrote:
> On Mon, Jul 17, 2023 at 06:27:09PM +0300, Vladimir Oltean wrote:
> > +static int dev_set_hwtstamp_phylib(struct net_device *dev,
> > +				   struct kernel_hwtstamp_config *cfg,
> > +				   struct netlink_ext_ack *extack)
> > +{
> > +	const struct net_device_ops *ops = dev->netdev_ops;
> > +	bool phy_ts = phy_has_hwtstamp(dev->phydev);
> > +	struct kernel_hwtstamp_config old_cfg = {};
> > +	bool changed = false;
> > +	int err;
> > +
> > +	cfg->source = phy_ts ? HWTSTAMP_SOURCE_PHYLIB : HWTSTAMP_SOURCE_NETDEV;
> > +
> > +	if (!phy_ts || (dev->priv_flags & IFF_SEE_ALL_HWTSTAMP_REQUESTS)) {
> 
> I suppose the idea here is that for something like mvpp2, which when we
> have PTP support for Marvell PHYs in general will want to prefer to use
> the MAC-based PTP rather than PHY-based, that driver needs to set
> IFF_SEE_ALL_HWTSTAMP_REQUESTS so that the ndo timestamp ops always get
> called? I didn't see this discussed in the commit message for this
> patch.

No; the plan for mvpp2-like situations is for Köry to:

- add UAPI to allow specifying the timestamping source (based on PHC ID,
  aka /dev/ptpN, probably)

- change the core policy (effectively this function) to prefer:
  - netdev-based timestamping by default (this reverses the current policy,
    to prevent future regressions when more phylib drivers gain
    timestamping support)
  - phylib-based timestamping for a selection of whitelisted phylib PHYs
    (this avoids regressions with existing phylib-based systems)
  - the user choice

The only thing that IFF_SEE_ALL_HWTSTAMP_REQUESTS does is to give the
netdev a hook for phylib timestamping operations, for completely
unrelated purposes (switch ports that become PTP-aware must stop
flooding PTP packets).