netdev - Re: [PATCH v3 1/1] net: phylink: add phylink_set_mac

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Date:   Sat, 8 Oct 2022 08:27:40 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Shenwei Wang <shenwei.wang@....com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        imx@...ts.linux.dev
Subject: Re: [PATCH v3 1/1] net: phylink: add phylink_set_mac_pm() helper

On Fri, Oct 07, 2022 at 10:42:46AM -0500, Shenwei Wang wrote:
> +/**
> + * phylink_set_mac_pm() - set phydev->mac_managed_pm to true
> + * @pl: a pointer to a &struct phylink returned from phylink_create()
> + *
> + * Set the phydev->mac_managed_pm, which is under the phylink instance
> + * specified by @pl, to true. This is to indicate that the MAC driver is
> + * responsible for PHY PM.
> + *
> + * The function can be called in the end of net_device_ops ndo_open() method
> + * or any place after phy is connected.

May I suggest a different wording:

"If the driver wishes to use this feature, this function should be
called each time after the driver connects a PHY with phylink."

This makes it clear that after one of:

phylink_connect_phy()
phylink_of_phy_connect()
phylink_fwnode_phy_connect()

has been called, and the driver wants to call this function, the driver
needs to call this every time just after the driver connects a PHY.

The alternative is that we store this information away when this
function is called, and always update the phydev when one is
connected.

There is also the question whether this should also be applied to PHYs
on SFP modules or not. Should a network driver using mac managed PM, but
also supports SFPs, and a copper SFP is plugged in with an accessible
PHY, what should happen if the system goes into a low power state?

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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