netdev - Re: [PATCH 2/2] net: phy: marvell-88q2xxx: Prevent reading temperature with asserted reset

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Message-ID: <Z7YUyNVR3mI35pel@eichest-laptop>
Date: Wed, 19 Feb 2025 18:28:40 +0100
From: Stefan Eichenberger <eichest@...il.com>
To: Dimitri Fedrau <dima.fedrau@...il.com>
Cc: Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Niklas Söderlund <niklas.soderlund+renesas@...natech.se>,
	Gregor Herburger <gregor.herburger@...tq-group.com>,
	Geert Uytterhoeven <geert@...ux-m68k.org>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] net: phy: marvell-88q2xxx: Prevent reading
 temperature with asserted reset

Hi Dimitri,

On Wed, Feb 19, 2025 at 11:54:58AM +0100, Dimitri Fedrau wrote:
> Hi Stefan,
> 
> Am Wed, Feb 19, 2025 at 07:29:49AM +0100 schrieb Stefan Eichenberger:
> > Hi Dimitri,
> > 
> > On Tue, Feb 18, 2025 at 07:33:10PM +0100, Dimitri Fedrau wrote:
> > > If the PHYs reset is asserted it returns 0xffff for any read operation.
> > > Prevent reading the temperature in this case and return with an I/O error.
> > > Write operations are ignored by the device.
> > > 
> > > Fixes: a197004cf3c2 ("net: phy: marvell-88q2xxx: Fix temperature measurement with reset-gpios")
> > > Signed-off-by: Dimitri Fedrau <dima.fedrau@...il.com>
> > > ---
> > >  drivers/net/phy/marvell-88q2xxx.c | 6 ++++++
> > >  1 file changed, 6 insertions(+)
> > > 
> > > diff --git a/drivers/net/phy/marvell-88q2xxx.c b/drivers/net/phy/marvell-88q2xxx.c
> > > index 30d71bfc365597d77c34c48f05390db9d63c4af4..c1ae27057ee34feacb31c2e3c40b2b1769596408 100644
> > > --- a/drivers/net/phy/marvell-88q2xxx.c
> > > +++ b/drivers/net/phy/marvell-88q2xxx.c
> > > @@ -647,6 +647,12 @@ static int mv88q2xxx_hwmon_read(struct device *dev,
> > >  	struct phy_device *phydev = dev_get_drvdata(dev);
> > >  	int ret;
> > >  
> > > +	/* If the PHYs reset is asserted it returns 0xffff for any read
> > > +	 * operation. Return with an I/O error in this case.
> > > +	 */
> > > +	if (phydev->mdio.reset_state == 1)
> > > +		return -EIO;
> > > +
> > >  	switch (attr) {
> > >  	case hwmon_temp_input:
> > >  		ret = phy_read_mmd(phydev, MDIO_MMD_PCS,
> > > 
> > 
> > It makes sense to me. However, aren't most phys that allow reading
> > sensors over MDIO affected by this issue? I couldn't find anything
> > similar, are they ignoring that use-case?
> >
> Yes, you are right, but only if the PHYs hard reset is controlled with
> "reset-gpios" or similar. I didn't find anything about it too.

Okay, I see. Maybe at one point it can be generalized, but for now this
sounds good to me. Just address the inputs from Andrew.

Regards,
Stefan