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

From: "Russell King (Oracle)" <[email-masked]>
Date: Thu, 20 Feb 2025 09:36:49 +0000

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.

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?

-- 
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