Subject: Re: [PATCH net-next v2 5/5] net: phylink: provide fixed state for 1000base-X and 2500base-X

From: "Russell King (Oracle)" <[email-masked]>
Date: Tue, 14 Jan 2025 13:31:22 +0000

On Tue, Jan 14, 2025 at 02:57:39PM +0200, Vladimir Oltean wrote:
> On Mon, Jan 13, 2025 at 09:22:44AM +0000, Russell King (Oracle) wrote:
> > When decoding clause 22 state, if in-band is disabled and using either
> > 1000base-X or 2500base-X, rather than reporting link-down, we know the
> > speed, and we only support full duplex. Pause modes taken from XPCS.
> > 
> > This fixes a problem reported by Eric Woudstra.
> > 
> > Signed-off-by: Russell King (Oracle) <[email-masked]>
> > ---
> >  drivers/net/phy/phylink.c | 29 +++++++++++++++++++----------
> >  1 file changed, 19 insertions(+), 10 deletions(-)
> > 
> > diff --git a/drivers/net/phy/phylink.c b/drivers/net/phy/phylink.c
> > index b79f975bc164..ff0efb52189f 100644
> > --- a/drivers/net/phy/phylink.c
> > +++ b/drivers/net/phy/phylink.c
> > @@ -3882,27 +3882,36 @@ void phylink_mii_c22_pcs_decode_state(struct phylink_link_state *state,
> >  	if (!state->link)
> >  		return;
> >  
> > -	/* If in-band is disabled, then the advertisement data is not
> > -	 * meaningful.
> > -	 */
> > -	if (neg_mode != PHYLINK_PCS_NEG_INBAND_ENABLED)
> > -		return;
> > -
> >  	switch (state->interface) {
> >  	case PHY_INTERFACE_MODE_1000BASEX:
> > -		phylink_decode_c37_word(state, lpa, SPEED_1000);
> > +		if (neg_mode == PHYLINK_PCS_NEG_INBAND_ENABLED) {
> > +			phylink_decode_c37_word(state, lpa, SPEED_1000);
> > +		} else {
> > +			state->speed = SPEED_1000;
> > +			state->duplex = DUPLEX_FULL;
> > +			state->pause |= MLO_PAUSE_TX | MLO_PAUSE_RX;
> > +		}
> >  		break;
> >  
> >  	case PHY_INTERFACE_MODE_2500BASEX:
> > -		phylink_decode_c37_word(state, lpa, SPEED_2500);
> > +		if (neg_mode == PHYLINK_PCS_NEG_INBAND_ENABLED) {
> > +			phylink_decode_c37_word(state, lpa, SPEED_2500);
> > +		} else {
> > +			state->speed = SPEED_2500;
> > +			state->duplex = DUPLEX_FULL;
> > +			state->pause |= MLO_PAUSE_TX | MLO_PAUSE_RX;
> > +		}
> >  		break;
> 
> Are the "else" branches necessary, given the "else" branch from
> phylink_mac_pcs_get_state?
> 
> static void phylink_mac_pcs_get_state(struct phylink *pl,
> 				      struct phylink_link_state *state)
> {
> 	struct phylink_pcs *pcs;
> 	bool autoneg;
> 
> 	linkmode_copy(state->advertising, pl->link_config.advertising);
> 	linkmode_zero(state->lp_advertising);
> 	state->interface = pl->link_config.interface;
> 	state->rate_matching = pl->link_config.rate_matching;
> 	state->an_complete = 0;
> 	state->link = 1;
> 
> 	pcs = pl->pcs;
> 	if (!pcs || pcs->neg_mode)
> 		autoneg = pl->pcs_neg_mode == PHYLINK_PCS_NEG_INBAND_ENABLED;
> 	else
> 		autoneg = linkmode_test_bit(ETHTOOL_LINK_MODE_Autoneg_BIT,
> 					    state->advertising);
> 
> 	if (autoneg) {
> 		state->speed = SPEED_UNKNOWN;
> 		state->duplex = DUPLEX_UNKNOWN;
> 		state->pause = MLO_PAUSE_NONE;
> 	} else {						|
> 		state->speed =  pl->link_config.speed;		|
> 		state->duplex = pl->link_config.duplex;		| this
> 		state->pause = pl->link_config.pause;		|
> 	}							|

This is fine for cases where ethtool is used to turn autoneg off, but
not if we're in in-band mode and the PCS/PHY have decided to have
autoneg off - in that case, nothing sets pl->link_config.* to anything
sensible.

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