Re: [PATCH v2 net] net: phy: change devlink flag to AUTOREMOVE_SUPPLIER for non-SFP PHYs

[Maxime Chevallier]

Hi Wei,

On 02/02/2026 06:45, Wei Fang wrote:
> For the shared MDIO bus use case, multiple MACs will share the same MDIO
> bus. Therefore, these MACs all depend on this MDIO bus. If this shared
> MDIO bus is removed, all the PHY devices attached to this MDIO bus will
> also be removed. Consequently, the MAC driver should not access the PHY
> device, otherwise, it will lead to some potential crashes. Because the
> corresponding phydev and the mii_bus have been freed, some pointers have
> become invalid.
> 
> For example. Abhishek reported a crash issue that occurred if the MDIO
> bus driver was removed first, followed by the MAC driver. The crash log
> is as below.
> 
> Call trace:
>  __list_del_entry_valid_or_report+0xa8/0xe0
>  __device_link_del+0x40/0xf0
>  device_link_put_kref+0xb4/0xc8
>  device_link_del+0x38/0x58
>  phy_detach+0x2c/0x170
>  phy_disconnect+0x4c/0x70
>  phylink_disconnect_phy+0x6c/0xc0 [phylink]
>  stmmac_release+0x60/0x358 [stmmac]
> 
> Another example is the i.MX95-15x15 platform which has two ENETC ports.
> When all the external PHYs are managed the EMDIO (the MDIO controller),
> if the enetc driver is removed after the EMDIO driver. Users will see
> the below crash log and the console is hanged.
> 
> Call trace:
>  _phy_state_machine+0x230/0x36c (P)
>  phy_stop+0x74/0x190
>  phylink_stop+0x28/0xb8
>  enetc_close+0x28/0x8c
>  __dev_close_many+0xb4/0x1d8
>  netif_close_many+0x8c/0x13c
>  enetc4_pf_remove+0x2c/0x84
>  pci_device_remove+0x44/0xe8
> 
> To address this issue, Sarosh Hasan tried to change the devlink flag to
> DL_FLAG_AUTOREMOVE_SUPPLIER [1], so that the MAC driver will be removed
> along with the PHY driver. However, the solution does not take into
> account the hot-swappable PHY devices (SFP PHYs), so when the PHY device
> is unplugged, the MAC driver will automatically be removed, which is not
> the expected behavior. This issue should not exist for SFP PHYs, so based
> on the Sarosh's patch, the flag is changed to DL_FLAG_AUTOREMOVE_SUPPLIER
> for non-SFP PHYs.
> 
> Reported-by: Abhishek Chauhan (ABC) <quic_abchauha@xxxxxxxxxxx>
> Closes: https://lore.kernel.org/all/d696a426-40bb-4c1a-b42d-990fb690de5e@xxxxxxxxxxx/
> Link: https://lore.kernel.org/imx/20250703090041.23137-1-quic_sarohasa@xxxxxxxxxxx/ # [1]
> Fixes: bc66fa87d4fd ("net: phy: Add link between phy dev and mac dev")
> Suggested-by: Maxime Chevallier <maxime.chevallier@xxxxxxxxxxx>
> Signed-off-by: Wei Fang <wei.fang@xxxxxxx>

I gave that patch a test, with the following cases :

 - On Macchiatobin (we have PHYs that share an mdiobus).
When unbinding a PHY, the MAC dissapears as well :

#before :

# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 2048
    link/ether 00:51:82:42:42:00 brd ff:ff:ff:ff:ff:ff
3: eth1: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN group default qlen 2048
    link/ether 00:51:82:42:42:01 brd ff:ff:ff:ff:ff:ff
4: eth2: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 2048
    link/ether 00:51:82:42:42:02 brd ff:ff:ff:ff:ff:ff
5: eth3: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN group default qlen 2048
    link/ether 00:51:82:42:42:03 brd ff:ff:ff:ff:ff:ff

echo f212a600.mdio-mii:08 > /sys/devices/platform/cp0-bus/cp0-bus:bus@f2000000/f212a600.mdio/mdio_bus/f212a600.mdio-mii/f212a600.mdio-mii:08/driver/unbind

The MAC interface correctly disappears, but for some reason a lot of
other interfaces dissapeared as well (only eth0 is left, where I used to
have 4 different interfaces)

# after :

# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 2048
    link/ether 00:51:82:42:42:00 brd ff:ff:ff:ff:ff:ff



- I also tested the SFP PHY setup on a Cyclone V platform,
and it worked as expected (i.e. MAC didn't disappear under my
feet when removing a Copper SFP, but the devlink was still created when
the module was present) :

# ls /sys/class/devlink/ 
mdio_bus:i2c:sfp:16--platform:ff702000.ethernet

I don't have time to investigate why my interfaces are dissapearing
on mcbin, but OTHO  unbinding the devices manually isn't
something I do very often... It may or may not be related to this patch.

I'll let Russell and Andrew comment more on that as I may
still miss other cases, but as far as I can tell, this looks
OK.

Tested-by: Maxime Chevallier <maxime.chevallier@xxxxxxxxxxx>
Reviewed-by: Maxime Chevallier <maxime.chevallier@xxxxxxxxxxx>

Maxime