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

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Message-ID: <0d29a5ee-8a68-d0be-c524-6e3ee1f46802@gmail.com>
Date:   Wed, 22 May 2019 19:29:07 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Ioana Ciornei <ioana.ciornei@....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



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?
> 
> 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