netdev - Re: [PATCH net-next 2/2] net: phy: add phy_speed_down and phy_speed

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Message-ID: <20180711205518.GJ21430@lunn.ch>
Date:   Wed, 11 Jul 2018 22:55:18 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Heiner Kallweit <hkallweit1@...il.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        David Miller <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 2/2] net: phy: add phy_speed_down and
 phy_speed_up

> +/**
> + * phy_speed_down - set speed to lowest speed supported by both link partners
> + * @phydev: the phy_device struct
> + * @sync: perform action synchronously
> + *
> + * Description: Typically used to save energy when waiting for a WoL packet
> + */
> +int phy_speed_down(struct phy_device *phydev, bool sync)

This sync parameter needs some more thought. I'm not sure it is safe.

How does a PHY trigger a WoL wake up? I guess some use the interrupt
pin. How does a PHY indicate auto-neg has completed? It triggers an
interrupt. So it seems like there is a danger here we suspend, and
then wake up 2 seconds later when auto-neg has completed.

I'm not sure we can safely suspend until auto-neg has completed.

> +/**
> + * phy_speed_up - (re)set advertised speeds to all supported speeds
> + * @phydev: the phy_device struct
> + * @sync: perform action synchronously
> + *
> + * Description: Used to revert the effect of phy_speed_down
> + */
> +int phy_speed_up(struct phy_device *phydev, bool sync)

And here, i'm thinking the opposite. A MAC driver needs to be ready
for the PHY state to change at any time. So why do we need to wait?
Just let the normal mechanisms inform the MAC when the link is up.

     Andrew