netdev - RE: [RFC PATCH net-next 5/9] net: phylink: Add phylink_create

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Message-ID: <VI1PR0402MB28006FF30E571E71F1AA1278E0010@VI1PR0402MB2800.eurprd04.prod.outlook.com>
Date:   Thu, 23 May 2019 12:10:47 +0000
From:   Ioana Ciornei <ioana.ciornei@....com>
To:     Florian Fainelli <f.fainelli@...il.com>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "andrew@...n.ch" <andrew@...n.ch>,
        "hkallweit1@...il.com" <hkallweit1@...il.com>,
        "maxime.chevallier@...tlin.com" <maxime.chevallier@...tlin.com>,
        "olteanv@...il.com" <olteanv@...il.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>
Subject: RE: [RFC PATCH net-next 5/9] net: phylink: Add phylink_create_raw


> Subject: Re: [RFC PATCH net-next 5/9] net: phylink: Add phylink_create_raw
> 
> 
> 
> On 5/22/2019 7:25 PM, Florian Fainelli wrote:
> >
> >
> > On 5/22/2019 6:20 PM, Ioana Ciornei wrote:
> >> This adds a new entry point to PHYLINK that does not require a
> >> net_device structure.
> >>
> >> The main intended use are DSA ports that do not have net devices
> >> registered for them (mainly because doing so would be redundant - see
> >> Documentation/networking/dsa/dsa.rst for details). So far DSA has
> >> been using PHYLIB fixed PHYs for these ports, driven manually with
> >> genphy instead of starting a full PHY state machine, but this does
> >> not scale well when there are actual PHYs that need a driver on those
> >> ports, or when a fixed-link is requested in DT that has a speed
> >> unsupported by the fixed PHY C22 emulation (such as SGMII-2500).
> >>
> >> The proposed solution comes in the form of a notifier chain owned by
> >> the PHYLINK instance, and the passing of phylink_notifier_info
> >> structures back to the driver through a blocking notifier call.
> >>
> >> The event API exposed by the new notifier mechanism is a 1:1 mapping
> >> to the existing PHYLINK mac_ops, plus the PHYLINK fixed-link callback.
> >>
> >> Both the standard phylink_create() function, as well as its raw
> >> variant, call the same underlying function which initializes either
> >> the netdev field or the notifier block of the PHYLINK instance.
> >>
> >> All PHYLINK driver callbacks have been extended to call the notifier
> >> chain in case the instance is a raw one.
> >>
> >> Signed-off-by: Ioana Ciornei <ioana.ciornei@....com>
> >> Signed-off-by: Vladimir Oltean <olteanv@...il.com>
> >> ---
> >
> > [snip]
> >
> >> +	struct phylink_notifier_info info = {
> >> +		.link_an_mode = pl->link_an_mode,
> >> +		/* Discard const pointer */
> >> +		.state = (struct phylink_link_state *)state,
> >> +	};
> >> +
> >>  	netdev_dbg(pl->netdev,
> >>  		   "%s: mode=%s/%s/%s/%s adv=%*pb pause=%02x link=%u
> an=%u\n",
> >>  		   __func__, phylink_an_mode_str(pl->link_an_mode),
> >> @@ -299,7 +317,12 @@ static void phylink_mac_config(struct phylink *pl,
> >>  		   __ETHTOOL_LINK_MODE_MASK_NBITS, state->advertising,
> >>  		   state->pause, state->link, state->an_enabled);
> >
> > Don't you need to guard that netdev_dbg() with an if (pl->ops) to
> > avoid de-referencing a NULL net_device?
> >


The netdev_* print will not dereference a NULL net_device since it has explicit checks agains this.
Instead it will just print (net/core/dev.c, __netdev_printk):

	printk("%s(NULL net_device): %pV", level, vaf);


> > Another possibility could be to change the signature of the
> > phylink_mac_ops to take an opaque pointer and in the case where we
> > called phylink_create() and passed down a net_device pointer, we
> > somehow remember that for doing any operation that requires a
> > net_device (printing, setting carrier). We lose strict typing in doing
> > that, but we'd have fewer places to patch for a blocking notifier call.
> >
> 
> Or even make those functions part of phylink_mac_ops such that the caller
> could pass an .carrier_ok callback which is netif_carrier_ok() for a net_device,
> else it's NULL, same with printing functions if desired...
> --
> Florian


Let me see if I understood this correctly. I presume that any API that we add should not break any current PHYLINK users.

You suggest to change the prototype of the phylink_mac_ops from

	void (*validate)(struct net_device *ndev, unsigned long *supported,
			 struct phylink_link_state *state);

to something that takes a void pointer:

	void (*validate)(void *dev, unsigned long *supported,
			 struct phylink_link_state *state);

This would imply that the any function in PHYLINK would have to somehow differentiate if the dev provided is indeed a net_device or another structure in order to make the decision if netif_carrier_off should be called or not (this is so we do not break any drivers using PHYLINK). I cannot see how this judgement can be made.

--
Ioana