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

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Message-ID: <Z7V6XZ7VRTkYNi2G@eichest-laptop>
Date: Wed, 19 Feb 2025 07:29:49 +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 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?

Regards,
Stefan