Re: [PATCH net] net: mii: Fix unknown speed after link up

[Linmao Li]

在 2026/10/1 5:47, Andrew Lunn 写道:
> On Wed, Sep 30, 2026 at 07:38:42PM +0800, Linmao Li wrote:
> > mii_ethtool_get_link_ksettings() reads BMSR only once. Since
> > BMSR_LSTATUS is latched low, the first query after link up can
> > report SPEED_UNKNOWN even though the link is already up.
> >
> > This is seen with r8152, which detects carrier using a MAC register
> > without clearing the BMSR latch. NetworkManager can then keep
> > reporting 0 Mb/s until the next carrier change.
> >
> > Read BMSR twice to obtain the current link status, as mii_link_ok()
> > already does.
> There is a reason for this latch behaviour, so you should not ignore
> it. It ensures a link down is reported, even if it is for a short
> period.
>
> I suggest you change the code to detect link based on BMSR, not a MAC
> register. Better still, throw away all the mii code and port it to
> phylink. A lot of code will go away because phylink/phylib and PHY
> drivers will implement it.
Hi Andrew,

Thanks for the review.

The existing read in mii_ethtool_get_link_ksettings() already clears
the latch, but I understand your concern about preserving short
link-down events.

For a focused r8152 fix, would it be acceptable to read BMSR once
before netif_carrier_on(), only when set_carrier() is transitioning
from carrier off to on? This would retain the existing MAC-based
carrier detection and clear the latched status before announcing
link up.

Or would you prefer changing carrier detection itself to use BMSR?
Could a phylink conversion be handled separately?

Thanks,
Linmao

>      Andrew
>
> ---
> pw-bot: cr