i2c: i801: Call i2c_register_spd for muxed child segments

Once the gpio mux driver binds to the "i2c-mux-gpio" platform device,
this creates the i2c adapters for the muxed child segments.
We can use the bus notifier mechanism to check for creation of the
child i2c adapters, and call i2c_register_spd() for them. This allows
to detect all DIMM's on systems with more than 8 memory slots.
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>

drivers/i2c/busses/i2c-i801.c

@@ -105,6 +105,7 @@
 #include <linux/ioport.h>
 #include <linux/init.h>
 #include <linux/i2c.h>
+#include <linux/i2c-mux.h>
 #include <linux/i2c-smbus.h>
 #include <linux/acpi.h>
 #include <linux/io.h>
@@ -291,6 +292,7 @@ struct i801_priv {
 #if IS_ENABLED(CONFIG_I2C_MUX_GPIO) && defined CONFIG_DMI
 	struct platform_device *mux_pdev;
 	struct gpiod_lookup_table *lookup;
+	struct notifier_block mux_notifier_block;
 #endif
 	struct platform_device *tco_pdev;
 
@@ -1394,6 +1396,23 @@ static const struct dmi_system_id mux_dmi_table[] = {
 	{ }
 };
 
+static int i801_notifier_call(struct notifier_block *nb, unsigned long action,
+			      void *data)
+{
+	struct i801_priv *priv = container_of(nb, struct i801_priv, mux_notifier_block);
+	struct device *dev = data;
+
+	if (action != BUS_NOTIFY_ADD_DEVICE ||
+	    dev->type != &i2c_adapter_type ||
+	    i2c_root_adapter(dev) != &priv->adapter)
+		return NOTIFY_DONE;
+
+	/* Call i2c_register_spd for muxed child segments */
+	i2c_register_spd(to_i2c_adapter(dev));
+
+	return NOTIFY_OK;
+}
+
 /* Setup multiplexing if needed */
 static void i801_add_mux(struct i801_priv *priv)
 {
@@ -1430,6 +1449,9 @@ static void i801_add_mux(struct i801_priv *priv)
 					       mux_config->gpios[i], "mux", 0);
 	gpiod_add_lookup_table(lookup);
 
+	priv->mux_notifier_block.notifier_call = i801_notifier_call;
+	if (bus_register_notifier(&i2c_bus_type, &priv->mux_notifier_block))
+		return;
 	/*
 	 * Register the mux device, we use PLATFORM_DEVID_NONE here
 	 * because since we are referring to the GPIO chip by name we are
@@ -1451,6 +1473,7 @@ static void i801_add_mux(struct i801_priv *priv)
 
 static void i801_del_mux(struct i801_priv *priv)
 {
+	bus_unregister_notifier(&i2c_bus_type, &priv->mux_notifier_block);
 	platform_device_unregister(priv->mux_pdev);
 	gpiod_remove_lookup_table(priv->lookup);
 }