drm/xe/doc: Add documentation for Execution Queues

Add documentation for Xe Execution Queues and add xe_exec_queue.rst
file.

v2: Add info about how Execution queue interfaces
with other components in the driver (Matt Brost)

Signed-off-by: Niranjana Vishwanathapura <[e-mail]>
Reviewed-by: Matthew Brost <[e-mail]>
Reviewed-by: Lucas De Marchi <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Lucas De Marchi <[e-mail]>

Documentation/gpu/xe/index.rst

···
    xe_mm
    xe_map
    xe_migrate
+   xe_exec_queue
    xe_cs
    xe_pm
    xe_gt_freq

Documentation/gpu/xe/xe_exec_queue.rst

···
+.. SPDX-License-Identifier: (GPL-2.0+ OR MIT)
+
+===============
+Execution Queue
+===============
+
+.. kernel-doc:: drivers/gpu/drm/xe/xe_exec_queue.c
+   :doc: Execution Queue
+
+Internal API
+============
+
+.. kernel-doc:: drivers/gpu/drm/xe/xe_exec_queue_types.h
+   :internal:
+
+.. kernel-doc:: drivers/gpu/drm/xe/xe_exec_queue.h
+   :internal:
+
+.. kernel-doc:: drivers/gpu/drm/xe/xe_exec_queue.c
+   :internal:

drivers/gpu/drm/xe/xe_exec_queue.c

···
 #include "xe_vm.h"
 #include "xe_pxp.h"
 
+/**
+ * DOC: Execution Queue
+ *
+ * An Execution queue is an interface for the HW context of execution.
+ * The user creates an execution queue, submits the GPU jobs through those
+ * queues and in the end destroys them.
+ *
+ * Execution queues can also be created by XeKMD itself for driver internal
+ * operations like object migration etc.
+ *
+ * An execution queue is associated with a specified HW engine or a group of
+ * engines (belonging to the same tile and engine class) and any GPU job
+ * submitted on the queue will be run on one of these engines.
+ *
+ * An execution queue is tied to an address space (VM). It holds a reference
+ * of the associated VM and the underlying Logical Ring Context/s (LRC/s)
+ * until the queue is destroyed.
+ *
+ * The execution queue sits on top of the submission backend. It opaquely
+ * handles the GuC and Execlist backends whichever the platform uses, and
+ * the ring operations the different engine classes support.
+ */
+
 enum xe_exec_queue_sched_prop {
 	XE_EXEC_QUEUE_JOB_TIMEOUT = 0,
 	XE_EXEC_QUEUE_TIMESLICE = 1,