net: dsa: sja1105: Check for PHY mode mismatches with what PHYLINK reports

PHYLINK being designed with PHYs in mind that can change MII protocol,
for correct operation it is necessary to ensure that the PHY interface
mode stays the same (otherwise clear the supported bit mask, as
required).

Because this is just a hypothetical situation for now, we don't bother
to check whether we could actually support the new PHY interface mode.
Actually we could modify the xMII table, reset the switch and send an
updated static configuration, but adding that would just be dead code.

Cc: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/sja1105/sja1105_main.c

@@ -766,12 +766,46 @@ static int sja1105_adjust_port_config(struct sja1105_private *priv, int port,
 	return sja1105_clocking_setup_port(priv, port);
 }
 
+/* The SJA1105 MAC programming model is through the static config (the xMII
+ * Mode table cannot be dynamically reconfigured), and we have to program
+ * that early (earlier than PHYLINK calls us, anyway).
+ * So just error out in case the connected PHY attempts to change the initial
+ * system interface MII protocol from what is defined in the DT, at least for
+ * now.
+ */
+static bool sja1105_phy_mode_mismatch(struct sja1105_private *priv, int port,
+				      phy_interface_t interface)
+{
+	struct sja1105_xmii_params_entry *mii;
+	sja1105_phy_interface_t phy_mode;
+
+	mii = priv->static_config.tables[BLK_IDX_XMII_PARAMS].entries;
+	phy_mode = mii->xmii_mode[port];
+
+	switch (interface) {
+	case PHY_INTERFACE_MODE_MII:
+		return (phy_mode != XMII_MODE_MII);
+	case PHY_INTERFACE_MODE_RMII:
+		return (phy_mode != XMII_MODE_RMII);
+	case PHY_INTERFACE_MODE_RGMII:
+	case PHY_INTERFACE_MODE_RGMII_ID:
+	case PHY_INTERFACE_MODE_RGMII_RXID:
+	case PHY_INTERFACE_MODE_RGMII_TXID:
+		return (phy_mode != XMII_MODE_RGMII);
+	default:
+		return true;
+	}
+}
+
 static void sja1105_mac_config(struct dsa_switch *ds, int port,
 			       unsigned int link_an_mode,
 			       const struct phylink_link_state *state)
 {
 	struct sja1105_private *priv = ds->priv;
 
+	if (sja1105_phy_mode_mismatch(priv, port, state->interface))
+		return;
+
 	sja1105_adjust_port_config(priv, port, state->speed);
 }
 
@@ -804,6 +838,16 @@ static void sja1105_phylink_validate(struct dsa_switch *ds, int port,
 
 	mii = priv->static_config.tables[BLK_IDX_XMII_PARAMS].entries;
 
+	/* include/linux/phylink.h says:
+	 *     When @state->interface is %PHY_INTERFACE_MODE_NA, phylink
+	 *     expects the MAC driver to return all supported link modes.
+	 */
+	if (state->interface != PHY_INTERFACE_MODE_NA &&
+	    sja1105_phy_mode_mismatch(priv, port, state->interface)) {
+		bitmap_zero(supported, __ETHTOOL_LINK_MODE_MASK_NBITS);
+		return;
+	}
+
 	/* The MAC does not support pause frames, and also doesn't
 	 * support half-duplex traffic modes.
 	 */