driver core: bus: add irq_get_affinity callback to bus_type

Introducing a callback in struct bus_type so that a subsystem
can hook up the getters directly. This approach avoids exposing
random getters in any subsystems APIs.

Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Daniel Wagner <wagi@kernel.org>
Link: https://lore.kernel.org/r/20241202-refactor-blk-affinity-helpers-v6-1-27211e9c2cd5@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/device/bus.h

@@ -48,6 +48,7 @@ struct fwnode_handle;
  *		will never get called until they do.
  * @remove:	Called when a device removed from this bus.
  * @shutdown:	Called at shut-down time to quiesce the device.
+ * @irq_get_affinity:	Get IRQ affinity mask for the device on this bus.
  *
  * @online:	Called to put the device back online (after offlining it).
  * @offline:	Called to put the device offline for hot-removal. May fail.
@@ -87,6 +88,8 @@ struct bus_type {
 	void (*sync_state)(struct device *dev);
 	void (*remove)(struct device *dev);
 	void (*shutdown)(struct device *dev);
+	const struct cpumask *(*irq_get_affinity)(struct device *dev,
+			unsigned int irq_vec);
 
 	int (*online)(struct device *dev);
 	int (*offline)(struct device *dev);