Re: [PATCH net-next v3 10/47] net: phylink: Adjust link settings based on rate adaptation

[Sean Anderson]

On 7/16/22 4:17 PM, Andrew Lunn wrote:
> On Fri, Jul 15, 2022 at 05:59:17PM -0400, Sean Anderson wrote:
> > If the phy is configured to use pause-based rate adaptation, ensure that
> > the link is full duplex with pause frame reception enabled. Note that these
> > settings may be overridden by ethtool.
> >
> > Signed-off-by: Sean Anderson <sean.anderson@xxxxxxxx>
> > ---
> >
> > Changes in v3:
> > - New
> >
> >   drivers/net/phy/phylink.c | 4 ++++
> >   1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
> > index 7fa21941878e..7f65413aa778 100644
> > --- a/drivers/net/phy/phylink.c
> > +++ b/drivers/net/phy/phylink.c
> > @@ -1445,6 +1445,10 @@ static void phylink_phy_change(struct phy_device *phydev, bool up)
> >   	pl->phy_state.speed = phy_interface_speed(phydev->interface,
> >   						  phydev->speed);
> >   	pl->phy_state.duplex = phydev->duplex;
> > +	if (phydev->rate_adaptation == RATE_ADAPT_PAUSE) {
> > +		pl->phy_state.duplex = DUPLEX_FULL;
> > +		rx_pause = true;
> > +	}
>
> I would not do this. If the requirements for rate adaptation are not
> fulfilled, you should turn off rate adaptation.
>
> A MAC which knows rate adaptation is going on can help out, by not
> advertising 10Half, 100Half etc. Autoneg will then fail for modes
> where rate adaptation does not work.

OK, so maybe it is better to phylink_warn here. Something along the
lines of "phy using pause-based rate adaptation, but duplex is %s".

> The MAC should also be declaring what sort of pause it supports, so
> disable rate adaptation if it does not have async pause.

That's what we do in the previous patch.

The problem is that rx_pause and tx_pause are resolved based on our
advertisement and the link partner's advertisement. However, the link
partner may not support pause frames at all. In that case, we will get
rx_pause and tx_pause as false. However, we still want to enable rx_pause,
because we know that the phy will be emitting pause frames. And of course
the user can always force disable pause frames anyway through ethtool.

--Sean