Re: [RFC PATCH net-next 1/3] net: phy: add concept of shared storage for PHYs

[Russell King - ARM Linux admin <linux@armlinux.org.uk>]

On Tue, Apr 21, 2020 at 09:30:55PM +0200, Andrew Lunn wrote:
> > Speaking of it. Does anyone have an idea how I could create the hwmon
> > device without the PHY device? At the moment it is attached to the
> > first PHY device and is removed when the PHY is removed, although
> > there might be still other PHYs in this package. Its unlikely to
> > happen though, but if someone has a good idea how to handle that,
> > I'd give it a try.
> 
> There is a somewhat similar problem with Marvell Ethernet switches and
> their internal PHYs. The PHYs are the same as the discrete PHYs, and
> the usual Marvell PHY driver is used. But there is only one
> temperature sensor for the whole switch, and it is mapped into all the
> PHYs. So we end up creating multiple hwmon devices for the one
> temperature sensor, one per PHY.

And sometimes we really mess it up - like on the 88e6141:

cp1configspacef4000000mdio12a200switch04mdio14-mdio-e
Adapter: MDIO adapter
temp1:        -75.0°C

because DSA forces the 6390 PHY ID for this PHY, and the marvell
driver tries to drive the PHY as if it's a different switch, so
we end up reading a register that isn't meaningful.

So, imho, the current approach isn't as good as you think it is.

That aside from wasting memory allocating multiple sensors when
there's really only one.

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