net: phylink: provide fixed state for 1000base-X and 2500base-X

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) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Tested-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Link: https://patch.msgid.link/E1tXGei-000EtL-Fn@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: Russell King (Oracle)

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;
 
 	case PHY_INTERFACE_MODE_SGMII:
 	case PHY_INTERFACE_MODE_QSGMII:
-		phylink_decode_sgmii_word(state, lpa);
+		if (neg_mode == PHYLINK_PCS_NEG_INBAND_ENABLED)
+			phylink_decode_sgmii_word(state, lpa);
 		break;
+
 	case PHY_INTERFACE_MODE_QUSGMII:
-		phylink_decode_usgmii_word(state, lpa);
+		if (neg_mode == PHYLINK_PCS_NEG_INBAND_ENABLED)
+			phylink_decode_usgmii_word(state, lpa);
 		break;
 
 	default: