net: dsa: microchip: Set SPI as bus interface during reset for KSZ8463

At reset, the KSZ8463 uses a strap-based configuration to set SPI as
bus interface. SPI is the only bus supported by the driver. If the
required pull-ups/pull-downs are missing (by mistake or by design to
save power) the pins may float and the configuration can go wrong
preventing any communication with the switch.

Introduce a ksz8463_configure_straps_spi() function called during the
device reset. It relies on the 'straps-rxd-gpios' OF property and the
'reset' pinmux configuration to enforce SPI as bus interface.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Bastien Curutchet (Schneider Electric) <bastien.curutchet@bootlin.com>
Link: https://patch.msgid.link/20250918-ksz-strap-pins-v3-3-16662e881728@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/dsa/microchip/ksz_common.c b/drivers/net/dsa/microchip/ksz_common.c
index 9568cc391fe3ec0bf5341318f12efcd09aa74e5c..a962055bfdbd8fbfc135b2dec73c222a213985c4 100644 (file)
--- a/drivers/net/dsa/microchip/ksz_common.c
+++ b/drivers/net/dsa/microchip/ksz_common.c
@@ -23,6 +23,7 @@
 #include <linux/of_mdio.h>
 #include <linux/of_net.h>
 #include <linux/micrel_phy.h>
+#include <linux/pinctrl/consumer.h>
 #include <net/dsa.h>
 #include <net/ieee8021q.h>
 #include <net/pkt_cls.h>
@@ -5345,6 +5346,38 @@ static int ksz_parse_drive_strength(struct ksz_device *dev)
        return 0;
 }
 
+static int ksz8463_configure_straps_spi(struct ksz_device *dev)
+{
+       struct pinctrl *pinctrl;
+       struct gpio_desc *rxd0;
+       struct gpio_desc *rxd1;
+
+       rxd0 = devm_gpiod_get_index_optional(dev->dev, "straps-rxd", 0, GPIOD_OUT_LOW);
+       if (IS_ERR(rxd0))
+               return PTR_ERR(rxd0);
+
+       rxd1 = devm_gpiod_get_index_optional(dev->dev, "straps-rxd", 1, GPIOD_OUT_HIGH);
+       if (IS_ERR(rxd1))
+               return PTR_ERR(rxd1);
+
+       if (!rxd0 && !rxd1)
+               return 0;
+
+       if ((rxd0 && !rxd1) || (rxd1 && !rxd0))
+               return -EINVAL;
+
+       pinctrl = devm_pinctrl_get_select(dev->dev, "reset");
+       if (IS_ERR(pinctrl))
+               return PTR_ERR(pinctrl);
+
+       return 0;
+}
+
+static int ksz8463_release_straps_spi(struct ksz_device *dev)
+{
+       return pinctrl_select_default_state(dev->dev);
+}
+
 int ksz_switch_register(struct ksz_device *dev)
 {
        const struct ksz_chip_data *info;
@@ -5360,10 +5393,22 @@ int ksz_switch_register(struct ksz_device *dev)
                return PTR_ERR(dev->reset_gpio);
 
        if (dev->reset_gpio) {
+               if (of_device_is_compatible(dev->dev->of_node, "microchip,ksz8463")) {
+                       ret = ksz8463_configure_straps_spi(dev);
+                       if (ret)
+                               return ret;
+               }
+
                gpiod_set_value_cansleep(dev->reset_gpio, 1);
                usleep_range(10000, 12000);
                gpiod_set_value_cansleep(dev->reset_gpio, 0);
                msleep(100);
+
+               if (of_device_is_compatible(dev->dev->of_node, "microchip,ksz8463")) {
+                       ret = ksz8463_release_straps_spi(dev);
+                       if (ret)
+                               return ret;
+               }
        }
 
        mutex_init(&dev->dev_mutex);