netdev - Re: [PATCH v3 1/2] net: phy: Fix PHY AN done state machine for interrupt driven PHYs

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Date:   Tue, 28 Mar 2017 13:05:40 +0300
From:   Roger Quadros <rogerq@...com>
To:     <f.fainelli@...il.com>, <andrew@...n.ch>
CC:     <davem@...emloft.net>, <kyle.roeschley@...com>, <nsekhar@...com>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        "stable # v4 . 9+" <stable@...r.kernel.org>,
        Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        "Andrew F. Davis" <afd@...com>, "Nori, Sekhar" <nsekhar@...com>
Subject: Re: [PATCH v3 1/2] net: phy: Fix PHY AN done state machine for
 interrupt driven PHYs

+Andrew Davis & Sekhar.

Hi,

Andrew Davis posted a few comments offline which I'm clarifying here.

On 27/03/17 14:59, Roger Quadros wrote:
> The Ethernet link on an interrupt driven PHY was not coming up if the
> Ethernet cable was plugged before the Ethernet interface was brought up.
> 
> The PHY state machine seems to be stuck from RUNNING to AN state
> with no new interrupts from the PHY. So it doesn't know when the
> PHY Auto-negotiation has been completed and doesn't transition to RUNNING
> state with ANEG done thus netif_carrier_on() is never called.
> 
> NOTE: genphy_config_aneg() will not restart PHY Auto-negotiation of
> advertisement parameters didn't change.

Is phy->config_aneg expected to *always* restart auto-negotiation even if
advertisement parameters didn't change?
If so then we'll need to fix genphy_config_aneg().

> 
> Fix this by scheduling the PHY state machine in phy_start_aneg().
> There is no way of knowing in phy.c whether auto-negotiation was
> restarted or not by the PHY driver so we just wait for the next
> poll/interrupt to update the PHY state machine.
> 
> Fixes: 3c293f4e08b5 ("net: phy: Trigger state machine on state change and not polling.")
> Cc: stable <stable@...r.kernel.org> # v4.9+
> Signed-off-by: Roger Quadros <rogerq@...com>
> ---
> v3: Fix typo in commit message
> 
>  drivers/net/phy/phy.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/net/phy/phy.c b/drivers/net/phy/phy.c
> index 1be69d8..49dedf8 100644
> --- a/drivers/net/phy/phy.c
> +++ b/drivers/net/phy/phy.c
> @@ -630,6 +630,10 @@ 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);
> 

There is still room for optimization for interrupt driven PHYs as I still
see a delay of 1 second between "ifconfig ethx up" and link status coming up
if cable was already plugged in. In fact if Auto-negotiation was already completed
and not required to be restarted, the PHY state machine should have move from
AN to RUNNING instantly without expecting a PHY interrupt.

How can we get rid of the unnecessary delay in the case where auto-negotiation
is not restarted?
Should we check for phy_aneg_done() immediately after issuing a phy_start_aneg()
in phy_state_machine() and switch from PHY_AN to PHY_RUNNING?

This should avoid the need to re-schedule the state machine in phy_start_angeg().

cheers,
-roger