Re: [PATCH] net: dsa: mv88e6xxx: prevent 2500BASEX mode override

[Russell King - ARM Linux admin <linux@armlinux.org.uk>]

On Mon, Feb 15, 2021 at 02:47:56PM +0100, Marek Behun wrote:
> On Mon, 15 Feb 2021 06:15:59 +0000
> Nathan Rossi <nathan@nathanrossi.com> wrote:
> 
> > diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
> > index 54aa942eed..5c52906b29 100644
> > --- a/drivers/net/dsa/mv88e6xxx/chip.c
> > +++ b/drivers/net/dsa/mv88e6xxx/chip.c
> > @@ -650,6 +650,13 @@ static void mv88e6xxx_validate(struct dsa_switch *ds, int port,
> >  	if (chip->info->ops->phylink_validate)
> >  		chip->info->ops->phylink_validate(chip, port, mask, state);
> >  
> > +	/* Advertise 2500BASEX only if 1000BASEX is not configured, this
> > +	 * prevents phylink_helper_basex_speed from always overriding the
> > +	 * 1000BASEX mode since auto negotiation is always enabled.
> > +	 */
> > +	if (state->interface == PHY_INTERFACE_MODE_1000BASEX)
> > +		phylink_clear(mask, 2500baseX_Full);
> > +
> 
> I don't quite like this. This problem should be either solved in
> phylink_helper_basex_speed() or somewhere in the mv88e6xxx code, but near
> the call to phylink_helper_basex_speed().
> 
> Putting a solution to the behaviour of phylink_helper_basex_speed() it
> into the validate() method when phylink_helper_basex_speed() is called
> from a different place will complicate debugging in the future. If
> we start solving problems in this kind of way, the driver will become
> totally unreadable, IMO.

If we can't switch between 1000base-X and 2500base-X, then we should
not be calling phylink_helper_basex_speed() - and only one of those
two capabilities should be set in the validation callback. I thought
there were DSA switches where we could program the CMODE to switch
between these two...

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