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

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Date:   Tue, 21 Apr 2020 23:19:48 +0200
From:   Michael Walle <michael@...le.cc>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        Florian Fainelli <f.fainelli@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S . Miller" <davem@...emloft.net>,
        Vladimir Oltean <vladimir.oltean@....com>
Subject: Re: [RFC PATCH net-next 1/3] net: phy: add concept of shared storage
 for PHYs

Am 2020-04-21 21:30, schrieb Andrew Lunn:
>> 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.
> 
> You could take the same approach here. Each PHY exposes a hwmon
> device?
> 
> Looking at
> static struct device *
> __hwmon_device_register(struct device *dev, const char *name, void 
> *drvdata,
>                         const struct hwmon_chip_info *chip,
>                         const struct attribute_group **groups)
> 
> I think it is O.K. to pass dev as NULL. You don't have to associate it
> to a device. So you could create the hwmon device as part of package
> initialisation and put it into shared->priv.

I actually tried that before writing my mail. Have a look at commit
59df4f4e8e0b ("hwmon: (core) check parent dev != NULL when chip != 
NULL")

and the corresponding discussion here:
   https://patchwork.kernel.org/patch/10381759/

And if I'd had to choose, I'd prefer having one hwmon device on the
first PHY (with its drawback) rather than having it four times.

-michael