netdev - Re: [PATCH RFC net-next 7/7] net: stmmac: explain the phylink_speed_down() call in stmmac

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Message-ID: <aIiKuVwyzR4ZSitl@shell.armlinux.org.uk>
Date: Tue, 29 Jul 2025 09:47:53 +0100
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Andrew Lunn <andrew@...n.ch>
Cc: Heiner Kallweit <hkallweit1@...il.com>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	linux-arm-kernel@...ts.infradead.org,
	linux-stm32@...md-mailman.stormreply.com,
	Maxime Coquelin <mcoquelin.stm32@...il.com>, netdev@...r.kernel.org,
	Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH RFC net-next 7/7] net: stmmac: explain the
 phylink_speed_down() call in stmmac_release()

On Mon, Jul 28, 2025 at 07:29:09PM +0200, Andrew Lunn wrote:
> On Mon, Jul 28, 2025 at 04:46:02PM +0100, Russell King (Oracle) wrote:
> > The call to phylink_speed_down() looks odd on the face of it. Add a
> > comment to explain why this call is there.
> > 
> > Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
> > ---
> >  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> > 
> > diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> > index f44f8b1b0efa..0da5c29b8cb0 100644
> > --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> > +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> > @@ -4138,8 +4138,13 @@ static int stmmac_release(struct net_device *dev)
> >  	struct stmmac_priv *priv = netdev_priv(dev);
> >  	u32 chan;
> >  
> > +	/* If the PHY or MAC has WoL enabled, then the PHY will not be
> > +	 * suspended when phylink_stop() is called below. Set the PHY
> > +	 * to its slowest speed to save power.
> > +	 */
> >  	if (device_may_wakeup(priv->device))
> >  		phylink_speed_down(priv->phylink, false);
> > +
> 
> Is there a corresponding phylink_speed_up() somewhere else? Does that
> need a similar comment?

__stmmac_open() does:

        phylink_start(priv->phylink);
        /* We may have called phylink_speed_down before */
        phylink_speed_up(priv->phylink);

So yes, there is a corresponding call, and it's unconditional, so such
a comment there wouldn't make sense.

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