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

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Date:   Tue, 4 Dec 2018 14:58:13 +0200
From:   Anssi Hannula <anssi.hannula@...wise.fi>
To:     Heiner Kallweit <hkallweit1@...il.com>
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 3.12.2018 23:41, Heiner Kallweit wrote:
> 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?

No, I encountered this while tinkering with phy_start/stop() to look how
they interact with suspending phydevs as I wanted to suspend unused ones.

So I don't think there is any rush to fix this one.

>>> 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.

Yeah, sounds better indeed.

>>> 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;
>>>>  
>>>>

-- 
Anssi Hannula / Bitwise Oy