net/mlx5: EQ, Introduce atomic notifier chain subscription API

Use atomic_notifier_chain to fire firmware events at internal mlx5 core
components such as eswitch/fpga/clock/FW tracer/etc.., this is to
avoid explicit calls from low level mlx5_core to upper components and to
simplify the mlx5_core API for future developments.

Simply provide register/unregister notifiers API and call the notifier
chain on firmware async events.

Example: to subscribe to a FW event:
struct mlx5_nb port_event;

MLX5_NB_INIT(&port_event, port_event_handler, PORT_CHANGE);
mlx5_eq_notifier_register(mdev, &port_event);

where:
 - port_event_handler is the notifier block callback.
 - PORT_EVENT is the suffix of MLX5_EVENT_TYPE_PORT_CHANGE.

The above will guarantee that port_event_handler will receive all FW
events of the type MLX5_EVENT_TYPE_PORT_CHANGE.

To receive all FW/HW events one can subscribe to
MLX5_EVENT_TYPE_NOTIFY_ANY.

The next few patches will start moving all mlx5 core components to use
this new API and cleanup mlx5_eq_async_int misx handler from component
explicit calls and specific logic.

Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>

include/linux/mlx5/device.h

@@ -301,9 +301,15 @@ enum {
 	MLX5_EVENT_QUEUE_TYPE_DCT = 6,
 };
 
+/* mlx5 components can subscribe to any one of these events via
+ * mlx5_eq_notifier_register API.
+ */
 enum mlx5_event {
+	/* Special value to subscribe to any event */
+	MLX5_EVENT_TYPE_NOTIFY_ANY	   = 0x0,
+	/* HW events enum start: comp events are not subscribable */
 	MLX5_EVENT_TYPE_COMP		   = 0x0,
-
+	/* HW Async events enum start: subscribable events */
 	MLX5_EVENT_TYPE_PATH_MIG	   = 0x01,
 	MLX5_EVENT_TYPE_COMM_EST	   = 0x02,
 	MLX5_EVENT_TYPE_SQ_DRAINED	   = 0x03,
@@ -341,6 +347,8 @@ enum mlx5_event {
 	MLX5_EVENT_TYPE_FPGA_QP_ERROR      = 0x21,
 
 	MLX5_EVENT_TYPE_DEVICE_TRACER      = 0x26,
+
+	MLX5_EVENT_TYPE_MAX                = MLX5_EVENT_TYPE_DEVICE_TRACER + 1,
 };
 
 enum {