linux-kernel - Re: [PATCH net-next v2 2/2] net: phy: marvell-88q2xxx: Prevent hwmon access with asserted reset

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Message-ID: <20250220152214.GA40326@debian>
Date: Thu, 20 Feb 2025 16:22:14 +0100
From: Dimitri Fedrau <dima.fedrau@...il.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
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>,
	Niklas Söderlund <niklas.soderlund+renesas@...natech.se>,
	Gregor Herburger <gregor.herburger@...tq-group.com>,
	Stefan Eichenberger <eichest@...il.com>,
	Geert Uytterhoeven <geert@...ux-m68k.org>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v2 2/2] net: phy: marvell-88q2xxx: Prevent hwmon
 access with asserted reset

Hi Russell,

Am Thu, Feb 20, 2025 at 09:36:49AM +0000 schrieb Russell King (Oracle):
> On Thu, Feb 20, 2025 at 09:11:12AM +0100, Dimitri Fedrau wrote:
> > If the PHYs reset is asserted it returns 0xffff for any read operation.
> > This might happen if the user admins down the interface and wants to read
> > the temperature. Prevent reading the temperature in this case and return
> > with an network is down error. Write operations are ignored by the device
> > when reset is asserted, still return a network is down error in this
> > case to make the user aware of the operation gone wrong.
> 
> If we look at where mdio_device_reset() is called from:
> 
> 1. mdio_device_register() -> mdiobus_register_device() asserts reset
>    before adding the device to the device layer (which will then
>    cause the driver to be searched for and bound.)
> 
> 2. mdio_probe(), deasserts the reset signal before calling the MDIO
>    driver's ->probe method, which will be phy_probe().
> 
> 3. after a probe failure to re-assert the reset signal.
> 
> 4. after ->remove has been called.
> 

There is also phy_device_reset that calls mdio_device_reset.

> That is the sum total. So, while the driver is bound to the device,
> phydev->mdio.reset_state is guaranteed to be zero.
> 
> Therefore, is this patch fixing a real observed problem with the
> current driver?
>
Yes, when I admin up and afterwards down the network device then the PHYs
reset is asserted. In this case phy_detach is called which calls
phy_device_reset(phydev, 1), ...

Best regards,
Dimitri Fedrau