i2c: acpi: Add an i2c_acpi_client_count() helper function

We have 3 files now which have the need to count the number of
I2cSerialBus resources in an ACPI-device's resource-list.

Currently all implement their own helper function for this,
add a generic helper function to replace the 3 implementations.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20210803160044.158802-2-hdegoede@redhat.comAcked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Wolfram Sang <wsa@kernel.org>

drivers/i2c/i2c-core-acpi.c

@@ -69,6 +69,38 @@ bool i2c_acpi_get_i2c_resource(struct acpi_resource *ares,
 }
 EXPORT_SYMBOL_GPL(i2c_acpi_get_i2c_resource);
 
+static int i2c_acpi_resource_count(struct acpi_resource *ares, void *data)
+{
+	struct acpi_resource_i2c_serialbus *sb;
+	int *count = data;
+
+	if (i2c_acpi_get_i2c_resource(ares, &sb))
+		*count = *count + 1;
+
+	return 1;
+}
+
+/**
+ * i2c_acpi_client_count - Count the number of I2cSerialBus resources
+ * @adev:	ACPI device
+ *
+ * Returns the number of I2cSerialBus resources in the ACPI-device's
+ * resource-list; or a negative error code.
+ */
+int i2c_acpi_client_count(struct acpi_device *adev)
+{
+	int ret, count = 0;
+	LIST_HEAD(r);
+
+	ret = acpi_dev_get_resources(adev, &r, i2c_acpi_resource_count, &count);
+	if (ret < 0)
+		return ret;
+
+	acpi_dev_free_resource_list(&r);
+	return count;
+}
+EXPORT_SYMBOL_GPL(i2c_acpi_client_count);
+
 static int i2c_acpi_fill_info(struct acpi_resource *ares, void *data)
 {
 	struct i2c_acpi_lookup *lookup = data;

include/linux/i2c.h

@@ -1010,6 +1010,7 @@ struct acpi_resource_i2c_serialbus;
 #if IS_ENABLED(CONFIG_ACPI)
 bool i2c_acpi_get_i2c_resource(struct acpi_resource *ares,
 			       struct acpi_resource_i2c_serialbus **i2c);
+int i2c_acpi_client_count(struct acpi_device *adev);
 u32 i2c_acpi_find_bus_speed(struct device *dev);
 struct i2c_client *i2c_acpi_new_device(struct device *dev, int index,
 				       struct i2c_board_info *info);
@@ -1020,6 +1021,10 @@ static inline bool i2c_acpi_get_i2c_resource(struct acpi_resource *ares,
 {
 	return false;
 }
+static inline int i2c_acpi_client_count(struct acpi_device *adev)
+{
+	return 0;
+}
 static inline u32 i2c_acpi_find_bus_speed(struct device *dev)
 {
 	return 0;