intel_th: Allow subdevice drivers to bring in own attribute groups

Some subdevices (MSU, PTI) need to register their own driver-specific
attribute groups. Provide a way for those to pass their attribute
groups to the core driver in their driver structure so that the
core can take care of creating and removing them.

Signed-off-by: Alexander Shishkin <[e-mail]>
Reviewed-by: Laurent Fert <[e-mail]>

drivers/hwtracing/intel_th/core.c

···
 	if (ret)
 		return ret;
 
+	if (thdrv->attr_group) {
+		ret = sysfs_create_group(&thdev->dev.kobj, thdrv->attr_group);
+		if (ret) {
+			thdrv->remove(thdev);
+
+			return ret;
+		}
+	}
+
 	if (thdev->type == INTEL_TH_OUTPUT &&
 	    !intel_th_output_assigned(thdev))
 		ret = hubdrv->assign(hub, thdev);
···
 		if (err)
 			return err;
 	}
+
+	if (thdrv->attr_group)
+		sysfs_remove_group(&thdev->dev.kobj, thdrv->attr_group);
 
 	thdrv->remove(thdev);
 

drivers/hwtracing/intel_th/intel_th.h

···
  * @enable:	enable tracing for a given output device
  * @disable:	disable tracing for a given output device
  * @fops:	file operations for device nodes
+ * @attr_group:	attributes provided by the driver
  *
  * Callbacks @probe and @remove are required for all device types.
  * Switch device driver needs to fill in @assign, @enable and @disable
···
 	void			(*deactivate)(struct intel_th_device *thdev);
 	/* file_operations for those who want a device node */
 	const struct file_operations *fops;
+	/* optional attributes */
+	struct attribute_group	*attr_group;
 
 	/* source ops */
 	int			(*set_output)(struct intel_th_device *thdev,