netdev - Re: [PATCH net-next 4/8] net: dsa: mv88e6xxx: do not increment bus refcount

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Message-ID: <87k2hwq0h1.fsf@ketchup.mtl.sfl>
Date:	Fri, 10 Jun 2016 15:59:22 -0400
From:	Vivien Didelot <vivien.didelot@...oirfairelinux.com>
To:	Andrew Lunn <andrew@...n.ch>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel@...oirfairelinux.com,
	"David S. Miller" <davem@...emloft.net>,
	Florian Fainelli <f.fainelli@...il.com>
Subject: Re: [PATCH net-next 4/8] net: dsa: mv88e6xxx: do not increment bus refcount

Hi,

Andrew Lunn <andrew@...n.ch> writes:

> On Wed, Jun 08, 2016 at 08:44:52PM -0400, Vivien Didelot wrote:
>> The MDIO device probe and remove functions are respectively incrementing
>> and decrementing the bus refcount themselves. Since these bus level
>> actions are out of the device scope, remove them.
>
> I agree with the patch. But have you checked the mdio layer is doing
> the right thing? If not, we should fix that first.

So I added some printing after incrementing/decrementing the refcount in
get_device/put_device to track &ps->bus->dev, which name is "0.1".

Regardless having this patch or not, the refcount of the 0.1 mii_bus
device is 5 before loading the mv88e6xxx module on vf610-zii-dev-rev-b.

Below is a portion of dmesg:

    [    8.921647] get_device: 400d1000.etherne refcount: 4
    [    8.926225] get_device: 0.1 refcount: 2
    [    8.929561] get_device: mdio-mux refcount: 5
    [    8.934076] get_device: 0.1 refcount: 3
    [    8.937446] get_device: 0.1 refcount: 4
    [    8.940792] put_device: 0.1 refcount: 3
    [    8.944181] libphy: mdio_mux: probed
    [    8.947885] mdio_bus 0.1:00: mdio_device_register
    [    8.952649] get_device: 0.1:00 refcount: 2
    [    8.956283] get_device: 0.1 refcount: 4
    [    8.959838] get_device: 0.1:00 refcount: 3
    [    8.963991] get_device: 0.1:00 refcount: 4
    [    8.967598] put_device: 0.1:00 refcount: 3
    [    8.971298] get_device: 0.2 refcount: 2
    [    8.974687] get_device: mdio-mux refcount: 7

So it seems like of_ is managing the bus refcount on events such as a
new child node (0.1:00).

Thanks,

        Vivien