Merge branch 'net-dsa-lantiq_gswip-two-fixes-for-net-stable'

Martin Blumenstingl says:

====================
net: dsa: lantiq_gswip: two fixes for -net/-stable

While testing the lantiq_gswip driver in OpenWrt at least one board had
a non-working Ethernet port connected to an internal 100Mbit/s PHY22F
GPHY. The problem which could be observed:
- the PHY would detect the link just fine
- ethtool stats would see the TX counter rise
- the RX counter in ethtool was stuck at zero

It turns out that two independent patches are needed to fix this:
- first we need to enable the MII data lines also for internal PHYs
- second we need to program the GSWIP_MII_CFG registers for all ports
  except the CPU port

These two patches have also been tested by back-porting them on top of
Linux 5.4.86 in OpenWrt.

Special thanks to Hauke for debugging and brainstorming this on IRC
with me!
====================

Link: https://lore.kernel.org/r/20210103012544.3259029-1-martin.blumenstingl@googlemail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/dsa/lantiq_gswip.c

@@ -92,9 +92,7 @@
 					 GSWIP_MDIO_PHY_FDUP_MASK)
 
 /* GSWIP MII Registers */
-#define GSWIP_MII_CFG0			0x00
-#define GSWIP_MII_CFG1			0x02
-#define GSWIP_MII_CFG5			0x04
+#define GSWIP_MII_CFGp(p)		(0x2 * (p))
 #define  GSWIP_MII_CFG_EN		BIT(14)
 #define  GSWIP_MII_CFG_LDCLKDIS		BIT(12)
 #define  GSWIP_MII_CFG_MODE_MIIP	0x0
@@ -392,17 +390,9 @@ static void gswip_mii_mask(struct gswip_priv *priv, u32 clear, u32 set,
 static void gswip_mii_mask_cfg(struct gswip_priv *priv, u32 clear, u32 set,
 			       int port)
 {
-	switch (port) {
-	case 0:
-		gswip_mii_mask(priv, clear, set, GSWIP_MII_CFG0);
-		break;
-	case 1:
-		gswip_mii_mask(priv, clear, set, GSWIP_MII_CFG1);
-		break;
-	case 5:
-		gswip_mii_mask(priv, clear, set, GSWIP_MII_CFG5);
-		break;
-	}
+	/* There's no MII_CFG register for the CPU port */
+	if (!dsa_is_cpu_port(priv->ds, port))
+		gswip_mii_mask(priv, clear, set, GSWIP_MII_CFGp(port));
 }
 
 static void gswip_mii_mask_pcdu(struct gswip_priv *priv, u32 clear, u32 set,
@@ -822,9 +812,8 @@ static int gswip_setup(struct dsa_switch *ds)
 	gswip_mdio_mask(priv, 0xff, 0x09, GSWIP_MDIO_MDC_CFG1);
 
 	/* Disable the xMII link */
-	gswip_mii_mask_cfg(priv, GSWIP_MII_CFG_EN, 0, 0);
-	gswip_mii_mask_cfg(priv, GSWIP_MII_CFG_EN, 0, 1);
-	gswip_mii_mask_cfg(priv, GSWIP_MII_CFG_EN, 0, 5);
+	for (i = 0; i < priv->hw_info->max_ports; i++)
+		gswip_mii_mask_cfg(priv, GSWIP_MII_CFG_EN, 0, i);
 
 	/* enable special tag insertion on cpu port */
 	gswip_switch_mask(priv, 0, GSWIP_FDMA_PCTRL_STEN,
@@ -1541,8 +1530,6 @@ static void gswip_phylink_mac_link_up(struct dsa_switch *ds, int port,
 {
 	struct gswip_priv *priv = ds->priv;
 
-	/* Enable the xMII interface only for the external PHY */
-	if (interface != PHY_INTERFACE_MODE_INTERNAL)
 	gswip_mii_mask_cfg(priv, 0, GSWIP_MII_CFG_EN, port);
 }