drm/i915/gt: document with_intel_gt_pm_if_awake()

Add a kernel-doc markup to document this new macro.
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/b974905bd0f6b5308b91561cc85eeecd94f1452a.1658924372.git.mchehab@kernel.org

drivers/gpu/drm/i915/gt/intel_gt_pm.h

@@ -55,6 +55,14 @@ static inline void intel_gt_pm_might_put(struct intel_gt *gt)
 	for (tmp = 1, intel_gt_pm_get(gt); tmp; \
 	     intel_gt_pm_put(gt), tmp = 0)
 
+/**
+ * with_intel_gt_pm_if_awake - if GT is PM awake, get a reference to prevent
+ *	it to sleep, run some code and then asynchrously put the reference
+ *	away.
+ *
+ * @gt: pointer to the gt
+ * @wf: pointer to a temporary wakeref.
+ */
 #define with_intel_gt_pm_if_awake(gt, wf) \
 	for (wf = intel_gt_pm_get_if_awake(gt); wf; intel_gt_pm_put_async(gt), wf = 0)