Re: [PATCH net] net: phy: fix phy_uses_state_machine()

[Vladimir Oltean <vladimir.oltean@nxp.com>]

On Mon, Sep 01, 2025 at 10:09:17AM +0100, Russell King (Oracle) wrote:
> On Mon, Sep 01, 2025 at 11:42:25AM +0300, Vladimir Oltean wrote:
> > On Sun, Aug 31, 2025 at 05:38:11PM +0100, Russell King (Oracle) wrote:
> > > phydev->phy_link_change is initialised by phy_attach_direct(), and
> > > overridden by phylink. This means that a never-connected PHY will
> > > have phydev->phy_link_change set to NULL, which causes
> > > phy_uses_state_machine() to return true. This is incorrect.
> > 
> > Another nitpick regarding phrasing here: the never-connected PHY doesn't
> > _cause_ phy_uses_state_machine() to return true. It returns true _in
> > spite_ of the PHY never being connected: the non-NULL quality of
> > phydev->phy_link_change is not something that phy_uses_state_machine()
> > tests for.
> 
> No. What I'm saying is that if phydev->phy_link_change is set to NULL,
> _this_ causes phy_uses_state_machine() to return true and that
> behaviour incorrect.
> 
> The first part is describing _when_ phydev->phy_link_change is set to
> NULL.
> 
> It is not saying that a never-connected PHY directly causes
> phy_uses_state_machine() to return true.
> 
> I think my phrasing of this is totally fine, even re-reading it now.
> 
> -- 
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I think the language is sufficiently flexible for us to find a phrasing
that avoids all ambiguity. What about:

"It was assumed the only two valid values for phydev->phy_link_change
are phy_link_change() and phylink_phy_change(), thus phy_uses_state_machine()
was oversimplified to only compare with one of these values. There is a
third possible value (NULL), meaning that the PHY is unconnected, and
does not use the state machine. This logic misinterprets this case as
phy_uses_state_machine() == true, but in reality it should return false."