Re: Lockup in phy_probe() for MDIO device (Broadcom's switch)

From: "Rafał Miłecki" <zajec5@gmail.com>
To: "Russell King (Oracle)" <linux@armlinux.org.uk>
Cc: Andrew Lunn <andrew@lunn.ch>,
	Heiner Kallweit <hkallweit1@gmail.com>,
	Network Development <netdev@vger.kernel.org>,
	Florian Fainelli <f.fainelli@gmail.com>,
	BCM Kernel Feedback <bcm-kernel-feedback-list@broadcom.com>,
	Vivek Unune <npcomplete13@gmail.com>
Subject: Re: Lockup in phy_probe() for MDIO device (Broadcom's switch)
Date: Thu, 30 Sep 2021 14:14:54 +0200	[thread overview]
Message-ID: <f51658fb-0844-93fc-46d0-6b3a7ef36123@gmail.com> (raw)
In-Reply-To: <YVWjEQzJisT0HgHB@shell.armlinux.org.uk>

On 30.09.2021 13:44, Russell King (Oracle) wrote:
> On Thu, Sep 30, 2021 at 01:29:33PM +0200, Rafał Miłecki wrote:
>> On 30.09.2021 12:40, Russell King (Oracle) wrote:
>>> In phy_probe, can you add:
>>>
>>> 	WARN_ON(!(phydev->mdio.flags & MDIO_DEVICE_FLAG_PHY));
>>>
>>> just to make sure we have a real PHY device there please? Maybe also
>>> print the value of the flags argument.
>>>
>>> MDIO_DEVICE_FLAG_PHY is set by phy_create_device() before the mutex is
>>> initialised, so if it is set, the lock should be initialised.
>>>
>>> Maybe also print mdiodev->flags in mdio_device_register() as well, so
>>> we can see what is being registered and the flags being used for that
>>> device.
>>>
>>> Could it be that openwrt is carrying a patch that is causing this
>>> issue?
>>
>> I don't think there is any OpenWrt patch affecting that.
>>
>> MDIO_DEVICE_FLAG_PHY seems to be missing.
> 
> Right, so the mdio device being registered is a non-PHY MDIO device.
> It doesn't have a struct phy_device around it - and so any access
> outside of the mdio_device is an out-of-bounds access.

I can confirm that.

of_mdiobus_register() iterates over node children. It calls
of_mdiobus_child_is_phy() for the /mdio-mux@18003000/mdio@200/switch@0
and that returns 0. It results in calling of_mdiobus_register_device().

So we have MDIO device as expected. It's not a PHY device.

> Consequently, phylib should not be matching this device. The only
> remaining way I can see that this could happen is if a PHY driver has
> an OF compatible, which phylib drivers should never have.

It's actually OpenWrt's downstream swconfig-based b53 driver that
matches this device.

I'm confused as downstream b53_mdio.c calls phy_driver_register(). Why
does it match MDIO device then? I thought MDIO devices should be
matches only with drivers using mdio_driver_register().