netdev - Re: [RFC PATCH] net: phy: Don't miss phy_suspend() on PHY

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Date:   Tue, 21 Mar 2017 09:00:40 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Roger Quadros <rogerq@...com>, Andrew Lunn <andrew@...n.ch>
Cc:     davem@...emloft.net, kyle.roeschley@...com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] net: phy: Don't miss phy_suspend() on PHY_HALTED for
 PHYs with interrupts

On 03/21/2017 03:09 AM, Roger Quadros wrote:
> On 20/03/17 18:41, Florian Fainelli wrote:
>> On 03/16/2017 12:46 AM, Roger Quadros wrote:
>>> On 15/03/17 17:49, Andrew Lunn wrote:
>>>> On Wed, Mar 15, 2017 at 05:00:08PM +0200, Roger Quadros wrote:
>>>>> Andrew,
>>>>>
>>>>> On 15/03/17 16:08, Andrew Lunn wrote:
>>>>>> On Wed, Mar 15, 2017 at 03:51:27PM +0200, Roger Quadros wrote:
>>>>>>> Since commit 3c293f4e08b5 ("net: phy: Trigger state machine on state change and not polling.")
>>>>>>> phy_suspend() doesn't get called as part of phy_stop() for PHYs using
>>>>>>> interrupts because the phy state machine is never triggered after a phy_stop().
>>>>>>>
>>>>>>> Explicitly trigger the PHY state machine so that it can
>>>>>>> see the new PHY state (HALTED) and suspend the PHY.
>>>>>>>
>>>>>>> Signed-off-by: Roger Quadros <rogerq@...com>
>>>>>>
>>>>>> Hi Roger
>>>>>>
>>>>>> This seems sensible. It mirrors what phy_start() does.
>>>>>>
>>>>>> Reviewed-by: Andrew Lunn <andrew@...n.ch>
>>>>>
>>>>> The reason for this being an RFC was the following comment just before
>>>>> where I add the phy_trigger_machine()
>>>>>
>>>>>         /* Cannot call flush_scheduled_work() here as desired because
>>>>>          * of rtnl_lock(), but PHY_HALTED shall guarantee phy_change()
>>>>>          * will not reenable interrupts.
>>>>>          */
>>>>>
>>>>> Is this comment still applicable? If yes, is it OK to call
>>>>> phy_trigger_machine() there?
>>>>
>>>> Humm, good question.
>>>>
>>>> My _guess_ would be, calling it with sync=True could
>>>> deadlock. sync=False is probably safe. But lets see what Florian says.
>>>
>>> I agree that we should use phy_trigger_machine() with sync=False.
>>>
>>>>
>>>>>
>>>>>>
>>>>>> It does however lead to a follow up question. Are there other places
>>>>>> phydev->state is changed and it is missing a phy_trigger_machine()?
>>>>>>
>>>>>
>>>>> One other place I think we should add phy_trigger_machine() is phy_start_aneg().
>>>>
>>>> Humm, that might get us into a tight loop.
>>>>
>>>> phy_start_aneg() kicks the phy driver to start autoneg and sets
>>>> phydev->state = PHY_AN.
>>>>
>>>> phy_trigger_machine() triggers the state machine immediately. 
>>>>
>>>> In state PHY_AN, we check if aneg is done. If not, it sets needs_aneg
>>>> = true. At the end of the state machine, this then calls
>>>> phy_start_aneg(), and it all starts again.
>>>>
>>>> We are missing the 1s delay we have with polling. So for
>>>> phy_start_aneg(), we might need a phy_delayed_trigger_machine(), which
>>>> waits a second before doing anything?
>>>
>>> I think that should do the trick.
>>>
>>> How about this?
>>
>> This sounds like a possible fix indeed, however I would like to better
>> assess the impact on non interrupt driven PHYs before rolling such a change.
> 
> Is it safer if I add a check to do this only for interrupt driven PHYs?

Yes I think this is a good solution that would not impact polled PHYs.
Can you submit a formal patch for that change?

Thanks!

> 
> e.g.
> 
> diff --git a/drivers/net/phy/phy.c b/drivers/net/phy/phy.c
> index 4b855f2..e0f5755 100644
> --- a/drivers/net/phy/phy.c
> +++ b/drivers/net/phy/phy.c
> @@ -630,6 +630,9 @@ int phy_start_aneg(struct phy_device *phydev)
>  
>  out_unlock:
>  	mutex_unlock(&phydev->lock);
> +	if (!err && phy_interrupt_is_valid(phydev))
> +		queue_delayed_work(system_power_efficient_wq, &phydev->state_queue, HZ);
> +
>  	return err;
>  }
>  EXPORT_SYMBOL(phy_start_aneg);
> 


-- 
Florian