platform/x86: wmi: Add driver_override support

Add support for forcing the WMI driver core to bind
a certain WMI driver to a WMI device. This will be
necessary to support generic WMI drivers without an
ID table

Reviewed-by: Hans de Goede <[e-mail]>
Signed-off-by: Armin Wolf <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Reviewed-by: Ilpo Järvinen <[e-mail]>
Signed-off-by: Ilpo Järvinen <[e-mail]>

drivers/platform/x86/wmi.c

···
 }
 static DEVICE_ATTR_RO(expensive);
 
+static ssize_t driver_override_show(struct device *dev, struct device_attribute *attr,
+				    char *buf)
+{
+	struct wmi_device *wdev = to_wmi_device(dev);
+	ssize_t ret;
+
+	device_lock(dev);
+	ret = sysfs_emit(buf, "%s\n", wdev->driver_override);
+	device_unlock(dev);
+
+	return ret;
+}
+
+static ssize_t driver_override_store(struct device *dev, struct device_attribute *attr,
+				     const char *buf, size_t count)
+{
+	struct wmi_device *wdev = to_wmi_device(dev);
+	int ret;
+
+	ret = driver_set_override(dev, &wdev->driver_override, buf, count);
+	if (ret < 0)
+		return ret;
+
+	return count;
+}
+static DEVICE_ATTR_RW(driver_override);
+
 static struct attribute *wmi_attrs[] = {
 	&dev_attr_modalias.attr,
 	&dev_attr_guid.attr,
 	&dev_attr_instance_count.attr,
 	&dev_attr_expensive.attr,
+	&dev_attr_driver_override.attr,
 	NULL
 };
 ATTRIBUTE_GROUPS(wmi);
···
 {
 	struct wmi_block *wblock = dev_to_wblock(dev);
 
+	kfree(wblock->dev.driver_override);
 	kfree(wblock);
 }
 
···
 	struct wmi_driver *wmi_driver = drv_to_wdrv(driver);
 	struct wmi_block *wblock = dev_to_wblock(dev);
 	const struct wmi_device_id *id = wmi_driver->id_table;
+
+	/* When driver_override is set, only bind to the matching driver */
+	if (wblock->dev.driver_override)
+		return !strcmp(wblock->dev.driver_override, driver->name);
 
 	if (id == NULL)
 		return 0;

include/linux/wmi.h

···
  * struct wmi_device - WMI device structure
  * @dev: Device associated with this WMI device
  * @setable: True for devices implementing the Set Control Method
+ * @driver_override: Driver name to force a match; do not set directly,
+ *		     because core frees it; use driver_set_override() to
+ *		     set or clear it.
  *
  * This represents WMI devices discovered by the WMI driver core.
  */
 struct wmi_device {
 	struct device dev;
 	bool setable;
+	const char *driver_override;
 };
 
 /**