netdev - Re: [PATCH 2/2] net: phy: ensure autoneg is configured when resuming a phydev

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Date:   Mon, 3 Dec 2018 22:41:33 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Anssi Hannula <anssi.hannula@...wise.fi>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH 2/2] net: phy: ensure autoneg is configured when resuming
 a phydev

On 03.12.2018 11:43, Anssi Hannula wrote:
> On 1.12.2018 0:16, Heiner Kallweit wrote:
>> On 30.11.2018 19:45, Anssi Hannula wrote:
>>> When a PHY_HALTED phydev is resumed by phy_start(), it is set to
>>> PHY_RESUMING to wait for the link to come up.
>>>
>>> However, if the phydev was put to PHY_HALTED (by e.g. phy_stop()) before
>>> autonegotiation was ever started by phy_state_machine(), autonegotiation
>>> remains unconfigured, i.e. phy_config_aneg() is never called.
>>>
>> phy_stop() should only be called once the PHY was started. But it's
>> right that we don't have full control over it because misbehaving
>> drivers may call phy_stop() even if the PHY hasn't been started yet.
> 
> Having run phy_start() does not guarantee that the phy_state_machine()
> has been run at least once, though.
> 
> I was able to reproduce the issue by calling phy_start(); phy_stop().
> Then on the next phy_start() autoneg is not configured.
> 
Right, phy_start() schedules the state machine run, so there is a small
window where this can happen. Did you experience this in any real-life
scenario?

>> I think phy_error() and phy_stop() should be extended to set the state
>> to PHY_HALTED only if the PHY is in a started state, means:
>> don't touch the state if it's DOWN, READY, or HALTED.
>> In case of phy_error() it's more a precaution, because it's used within
>> phylib only and AFAICS it can be triggered from a started state only.
> 
> This wouldn't fix the issue that occurs when phy_stop() is called right
> after phy_start(), though, as PHY is in UP state then.
> 
After having removed state AN I was thinking already whether we really
need to have separate states READY and HALTED. I think we wouldn't
have this scenario if phy_stop() and phy_error() would set the state
to READY. Merging the two states requires some upfront work, but I have
some ideas in the back of my mind.
Overall this should be cleaner than the proposed workaround.

>>
>> So yes, there is a theoretical issue. But as you wrote already, I think
>> there's a better way to deal with it.
>>
>> For checking whether PHY is in a started state you could use the helper
>> which is being discussed here:
>> https://marc.info/?l=linux-netdev&m=154360368104946&w=2
>>
>>
>>> Fix that by going to PHY_UP instead of PHY_RESUMING if autonegotiation
>>> has never been configured.
>>>
>>> Signed-off-by: Anssi Hannula <anssi.hannula@...wise.fi>
>>> ---
>>>
>>> This doesn't feel as clean is I'd like to, though. Maybe there is a
>>> better way?
>>>
>>>
>>>  drivers/net/phy/phy.c | 11 ++++++++++-
>>>  include/linux/phy.h   |  2 ++
>>>  2 files changed, 12 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/net/phy/phy.c b/drivers/net/phy/phy.c
>>> index d46858694db9..7a650cce7599 100644
>>> --- a/drivers/net/phy/phy.c
>>> +++ b/drivers/net/phy/phy.c
>>> @@ -553,6 +553,8 @@ int phy_start_aneg(struct phy_device *phydev)
>>>  	if (err < 0)
>>>  		goto out_unlock;
>>>  
>>> +	phydev->autoneg_configured = 1;
>>> +
>>>  	if (phydev->state != PHY_HALTED) {
>>>  		if (AUTONEG_ENABLE == phydev->autoneg) {
>>>  			err = phy_check_link_status(phydev);
>>> @@ -893,7 +895,14 @@ void phy_start(struct phy_device *phydev)
>>>  				break;
>>>  		}
>>>  
>>> -		phydev->state = PHY_RESUMING;
>>> +		/* if autoneg/forcing was never configured, go back to PHY_UP
>>> +		 * to make that happen
>>> +		 */
>>> +		if (!phydev->autoneg_configured)
>>> +			phydev->state = PHY_UP;
>>> +		else
>>> +			phydev->state = PHY_RESUMING;
>>> +
>>>  		break;
>>>  	default:
>>>  		break;
>>> diff --git a/include/linux/phy.h b/include/linux/phy.h
>>> index 8f927246acdb..b306d5ed9d09 100644
>>> --- a/include/linux/phy.h
>>> +++ b/include/linux/phy.h
>>> @@ -389,6 +389,8 @@ struct phy_device {
>>>  	unsigned loopback_enabled:1;
>>>  
>>>  	unsigned autoneg:1;
>>> +	/* autoneg has been configured at least once */
>>> +	unsigned autoneg_configured:1;
>>>  	/* The most recently read link state */
>>>  	unsigned link:1;
>>>  
>>>
>