linux-kernel - Re: [PATCH net] net: phy: add device link between MAC device and MDIO device

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Message-ID: <cb94b647-c2a4-468d-ac1c-c5f18f0734f2@bootlin.com>
Date: Fri, 30 Jan 2026 09:29:38 +0100
From: Maxime Chevallier <maxime.chevallier@...tlin.com>
To: Wei Fang <wei.fang@....com>, Russell King <linux@...linux.org.uk>,
 Jakub Kicinski <kuba@...nel.org>
Cc: "andrew@...n.ch" <andrew@...n.ch>,
 "hkallweit1@...il.com" <hkallweit1@...il.com>,
 "florian.fainelli@...adcom.com" <florian.fainelli@...adcom.com>,
 "xiaolei.wang" <xiaolei.wang@...driver.com>,
 "davem@...emloft.net" <davem@...emloft.net>,
 "edumazet@...gle.com" <edumazet@...gle.com>,
 "pabeni@...hat.com" <pabeni@...hat.com>,
 "quic_abchauha@...cinc.com" <quic_abchauha@...cinc.com>,
 "quic_sarohasa@...cinc.com" <quic_sarohasa@...cinc.com>,
 "imx@...ts.linux.dev" <imx@...ts.linux.dev>,
 "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] net: phy: add device link between MAC device and MDIO
 device

Hi,

On 30/01/2026 04:41, Wei Fang wrote:
>> On Wed, Jan 28, 2026 at 08:15:01PM -0800, Jakub Kicinski wrote:
>>> On Mon, 26 Jan 2026 18:44:09 +0800 Wei Fang wrote:
>>>> The commit bc66fa87d4fd ("net: phy: Add link between phy dev and mac
>>>> dev") has created a device link between the MAC and the PHY if the
>>>> MAC uses a shared MDIO bus (The MDIO and the MAC are two separate
>> devices).
>>>> Sarosh Hasan tried to change the DL_FLAG_STATELESS flag to
>>>> DL_FLAG_AUTOREMOVE_SUPPLIER to fix the issue [1]. However, the
>>>> solution does not take into account the hot-swappable PHY devices (such as
>> SFP).
>>>> so when the PHY device is unplugged, the MAC driver will
>>>> automatically be removed, which is not the expected behavior.
>>>>
>>>> Therefore, to solve this issue of the shared MDIO bus, we create the
>>>> device link between the MAC device and the MDIO device, rather than
>>>> between the MAC device and the PHY device. And when the shared MDIO
>>>> bus is removed, all MAC drivers that depend on it will also be removed.
>>>
>>> Anyone willing to venture a review tag?
>>
>> No, I don't agrew with the patch.
>>
> 
> Is it because of SFP? If so, would the following modification be more
> reasonable, while SFP still follows the previous logic? I'm not sure if
> phydev->sfp_bus_attached can be used to distinguish between SFP
> PHYs and non-SFP PHYs.

If you want to know if the PHY is in an SFP module, you should use
phy_on_sfp() instead :

https://elixir.bootlin.com/linux/v6.18.6/source/include/linux/phy.h#L1766

It's set for this kind of setups :


               SFP module
+-----+      +-----------+
| MAC | ---- | PHY       |
+-----+      +--\--------+
                 \
                  \_ phy_on_sfp(phydev) == true


phydev->sfp_bus_attached is for the media converter user-case :

                            SFP Module
+-----+      +-----+      +------------+
| MAC | ---- | PHY | ---- |   ???      |
+-----+      +--\--+      +------------+
                 \
                  \_ phydev->sfp_bus_attached == true
> 
> Anyway, this problem has existed for a long time, and I think we should
> find a way to solve it in upstream. If there's a better approach, I can help
> verify it.

Sorry I wasn't available for most part of yesterday for that discussion.

I'll give a try to this patch today, with the above change and let you know
how this goes.

Maxime