Date:   Mon, 20 Mar 2017 15:07:02 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Niklas Cassel <niklas.cassel@...s.com>, peppe.cavallaro@...com,
        alexandre.torgue@...com, Joao.Pinto@...opsys.com
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] stmmac: call stmmac_init_phy from
 stmmac_dvr_probe

On 03/20/2017 11:34 AM, Niklas Cassel wrote:
> On 03/20/2017 06:43 PM, Florian Fainelli wrote:
>> On 03/20/2017 10:29 AM, Niklas Cassel wrote:
>>> From: Niklas Cassel <niklas.cassel@...s.com>
>>>
>>> It is usually possible to do
>>> ethtool -s autoneg on
>>> so that you trigger an autoneg before calling
>>> ip link set dev eth0 up
>> This is completely driver specific and there is no guarantee for this to
>> work universally across all device drivers because when your interface
>> is brought down, the most sensible thing to expect in return is that
>> your PHY is powered down (unless your interface participates in
>> Wake-on-LAN).
>>
>>> However, stmmac returns -EBUSY if !netif_running.
>>> The only reason for this appears to be that stmmac_init_phy
>>> is called from stmmac_open instead of from stmmac_dvr_probe.
>>>
>>> Move stmmac_init_phy to stmmac_dvr_probe so that ethool
>>> works as soon as register_netdev has been called.
>>> stmmac_check_ether_addr was also moved to probe,
>>> so that the ordering doesn't change.
>> Are you sure this is a good idea? There are many drivers that moved the
>> PHY probe into ndo_open() for mainly two things:
>>
>> - phy_connect() starts the PHY state machine and starting the state
>> machine without a network device running is kind of wasting cycles
>>
>> - if the interface is probed, but not used, you are keeping the Ethernet
>> link running without being able to service packets, which is at best a
>> waste of power
> 
> Hello Florian
> 
> Thank you for your input.
> I can see the point in keeping phy_connect in ndo_open.
> 
> What I dislike is the -EBUSY from stmmac_ethtool_get_link_ksettings,
> since this will create warnings in user space by our favorite monolith.
> (Please don't flame me, I dislike it as much as you guys.)
> 
> [ WARNING ] systemd-udevd[236]: link_config: could not get ethtool features for eth0
> [ WARNING ] systemd-udevd[236]: Could not set offload features of eth0: Device or resource busy

Then let's silence the warning, because it's not really helpful in the
first place.

> 
> 
> However, it is kind of sad that drivers are so inconsistent of what goes
> in probe and what goes in ndo_open...which is tied together with the
> whole mess of when certain ethtool commands work or do not work.

Well, inconsistent here is kind of big statement, what I meant to say is
that your proposed change actually makes thing inconsistent.

> 
> Do you know of a good way to avoid the -EBUSY in stmmac_ethtool_get_link_ksettings,
> but still keep phy_connect in ndo_open?

Let me rephrase this: doing an ethtool operation on an interface that is
not open is not a defined behavior which adheres to a contract with the
kernel. ethtool operations on interfaces that are DOWN, may succeed if
they do not involve a piece of hardware that needs to be active (e.g:
the PHY) but there is no guarantee that a) the change is immediately
applied, or b) that the results are consistent.

The best thing to do IMHO is just silence the warning, return an error
coed, and come back configuring the interface at a later time when it is
guaranteed to be operational.

> The current code checks netif_running(), which checks __LINK_STATE_START,
> which gets set by __dev_open().
> stmmac_ethtool_get_link_ksettings also returns -ENODEV if ndev->phydev == NULL.
> 


-- 
Florian

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