Re: [PATCH net] net: usb: lan78xx: only stop phylink if the interface is running

[Oleksij Rempel <o.rempel@pengutronix.de>]

On Fri, Oct 30, 2026 at 12:02:04AM +0800, YuanZhe Liu wrote:
> lan78xx_disconnect() unconditionally calls phylink_stop(), but
> phylink_start() is only called from lan78xx_open(). When the device is
> unplugged before the interface has been brought up, the attached PHY is
> still in PHY_READY and phy_stop() reports:
> 
>   called from state READY
>   WARNING: drivers/net/phy/phy.c:1670 at phy_stop+0xad/0x380
> 
> The same warning is emitted after an ifup/ifdown cycle, where the PHY is
> already in PHY_HALTED. Call phylink_stop() only when the network device is
> running, which is when phylink_start() has been called.
> 
> Fixes: e110bc825897 ("net: usb: lan78xx: Convert to PHYLINK for improved PHY and MAC management")
> Cc: stable@vger.kernel.org
> Co-developed-by: Bin Yu <byu@xidian.edu.cn>
> Signed-off-by: Bin Yu <byu@xidian.edu.cn>
> Co-developed-by: Cheng Wen <wencheng@xidian.edu.cn>
> Signed-off-by: Cheng Wen <wencheng@xidian.edu.cn>
> Signed-off-by: YuanZhe Liu <25031212351@stu.xidian.edu.cn>

Tested-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Oleksij Rempel <o.rempel@pengutronix.de>

I reproduced the phy_stop() warning on a LAN7850 behind an i.MX8MP, by
unbinding the driver or by writing 0 to the USB device's "authorized"
attribute:

- interface never opened: "called from state READY"
- after ifup and ifdown: "called from state HALTED"
- ifup/ifdown loop during the removal: "called from state HALTED"

On kernels before the phylink conversion, none of these three cases hit
the phy_stop() warning.

With this patch, none of them warns, on net-next and on ba28ef3ccfa9
("Merge branch 'convert-lan78xx-driver-to-the-phylink'") with
312c816c6bc3 ("net: usb: lan78xx: fix WARN in __netif_napi_del_locked on
disconnect") applied. Removals with the interface open, sending, with
link up, link down or link flapping did not warn either. I ran each
case twice per patched kernel, with lockdep, KASAN and kmemleak enabled.
After re-adding the device the interface came up again.

The suspend/resume problems in the Sashiko review are not caused or
fixed by this patch.

Best Regards,
Oleksij
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