net: dsa: b53: do not configure bcm63xx's IMP port interface

The IMP port is not a valid RGMII interface, but hard wired to internal,
so we shouldn't touch the undefined register B53_RGMII_CTRL_IMP.

While this does not seem to have any side effects, let's not touch it at
all, so limit RGMII configuration on bcm63xx to the actual RGMII ports.

Fixes: ce3bf94 ("net: dsa: b53: add support for BCM63xx RGMIIs")
Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://patch.msgid.link/20250602193953.1010487-4-jonas.gorski@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: KanjiMonster

drivers/net/dsa/b53/b53_common.c

@@ -22,6 +22,7 @@
 #include <linux/gpio.h>
 #include <linux/kernel.h>
 #include <linux/math.h>
+#include <linux/minmax.h>
 #include <linux/module.h>
 #include <linux/platform_data/b53.h>
 #include <linux/phy.h>
@@ -1322,24 +1323,17 @@ static void b53_adjust_63xx_rgmii(struct dsa_switch *ds, int port,
 				  phy_interface_t interface)
 {
 	struct b53_device *dev = ds->priv;
-	u8 rgmii_ctrl = 0, off;
+	u8 rgmii_ctrl = 0;
 
-	if (port == dev->imp_port)
-		off = B53_RGMII_CTRL_IMP;
-	else
-		off = B53_RGMII_CTRL_P(port);
-
-	b53_read8(dev, B53_CTRL_PAGE, off, &rgmii_ctrl);
+	b53_read8(dev, B53_CTRL_PAGE, B53_RGMII_CTRL_P(port), &rgmii_ctrl);
 	rgmii_ctrl &= ~(RGMII_CTRL_DLL_RXC | RGMII_CTRL_DLL_TXC);
 
-	if (port != dev->imp_port) {
-		if (is63268(dev))
-			rgmii_ctrl |= RGMII_CTRL_MII_OVERRIDE;
+	if (is63268(dev))
+		rgmii_ctrl |= RGMII_CTRL_MII_OVERRIDE;
 
-		rgmii_ctrl |= RGMII_CTRL_ENABLE_GMII;
-	}
+	rgmii_ctrl |= RGMII_CTRL_ENABLE_GMII;
 
-	b53_write8(dev, B53_CTRL_PAGE, off, rgmii_ctrl);
+	b53_write8(dev, B53_CTRL_PAGE, B53_RGMII_CTRL_P(port), rgmii_ctrl);
 
 	dev_dbg(ds->dev, "Configured port %d for %s\n", port,
 		phy_modes(interface));
@@ -1484,7 +1478,7 @@ static void b53_phylink_mac_config(struct phylink_config *config,
 	struct b53_device *dev = ds->priv;
 	int port = dp->index;
 
-	if (is63xx(dev) && port >= B53_63XX_RGMII0)
+	if (is63xx(dev) && in_range(port, B53_63XX_RGMII0, 4))
 		b53_adjust_63xx_rgmii(ds, port, interface);
 
 	if (mode == MLO_AN_FIXED) {