drm/amd/display: Use periodic detection for ipx/headless

[WHY]
Hotplug is not detected in headless (no eDP) mode on dcn35x.
With no display dcn35x goes to IPS2 powersaving state where HPD interrupt
is not handled.

[HOW]
Use idle worker thread for periodic detection of HPD in headless mode.
Reviewed-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Cc: Mario Limonciello <mario.limonciello@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Roman Li <roman.li@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h

@@ -989,4 +989,7 @@ void *dm_allocate_gpu_mem(struct amdgpu_device *adev,
 						  enum dc_gpu_mem_alloc_type type,
 						  size_t size,
 						  long long *addr);
+
+bool amdgpu_dm_is_headless(struct amdgpu_device *adev);
+
 #endif /* __AMDGPU_DM_H__ */

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_crtc.c

@@ -162,33 +162,63 @@ static void amdgpu_dm_crtc_set_panel_sr_feature(
 	}
 }
 
+bool amdgpu_dm_is_headless(struct amdgpu_device *adev)
+{
+	struct drm_connector *connector;
+	struct drm_connector_list_iter iter;
+	struct drm_device *dev;
+	bool is_headless = true;
+
+	if (adev == NULL)
+		return true;
+
+	dev = adev->dm.ddev;
+
+	drm_connector_list_iter_begin(dev, &iter);
+	drm_for_each_connector_iter(connector, &iter) {
+
+		if (connector->connector_type == DRM_MODE_CONNECTOR_WRITEBACK)
+			continue;
+
+		if (connector->status == connector_status_connected) {
+			is_headless = false;
+			break;
+		}
+	}
+	drm_connector_list_iter_end(&iter);
+	return is_headless;
+}
+
 static void amdgpu_dm_idle_worker(struct work_struct *work)
 {
 	struct idle_workqueue *idle_work;
 
 	idle_work = container_of(work, struct idle_workqueue, work);
 	idle_work->dm->idle_workqueue->running = true;
-	fsleep(HPD_DETECTION_PERIOD_uS);
-	mutex_lock(&idle_work->dm->dc_lock);
+
 	while (idle_work->enable) {
-		if (!idle_work->dm->dc->idle_optimizations_allowed)
+		fsleep(HPD_DETECTION_PERIOD_uS);
+		mutex_lock(&idle_work->dm->dc_lock);
+		if (!idle_work->dm->dc->idle_optimizations_allowed) {
+			mutex_unlock(&idle_work->dm->dc_lock);
 			break;
-
+		}
 		dc_allow_idle_optimizations(idle_work->dm->dc, false);
 
 		mutex_unlock(&idle_work->dm->dc_lock);
 		fsleep(HPD_DETECTION_TIME_uS);
 		mutex_lock(&idle_work->dm->dc_lock);
 
-		if (!amdgpu_dm_psr_is_active_allowed(idle_work->dm))
+		if (!amdgpu_dm_is_headless(idle_work->dm->adev) &&
+		    !amdgpu_dm_psr_is_active_allowed(idle_work->dm)) {
+			mutex_unlock(&idle_work->dm->dc_lock);
 			break;
+		}
 
-		dc_allow_idle_optimizations(idle_work->dm->dc, true);
+		if (idle_work->enable)
+			dc_allow_idle_optimizations(idle_work->dm->dc, true);
 		mutex_unlock(&idle_work->dm->dc_lock);
-		fsleep(HPD_DETECTION_PERIOD_uS);
-		mutex_lock(&idle_work->dm->dc_lock);
 	}
-	mutex_unlock(&idle_work->dm->dc_lock);
 	idle_work->dm->idle_workqueue->running = false;
 }
 

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c

@@ -1239,8 +1239,11 @@ void dm_helpers_enable_periodic_detection(struct dc_context *ctx, bool enable)
 {
 	struct amdgpu_device *adev = ctx->driver_context;
 
-	if (adev->dm.idle_workqueue)
+	if (adev->dm.idle_workqueue) {
 		adev->dm.idle_workqueue->enable = enable;
+		if (enable && !adev->dm.idle_workqueue->running && amdgpu_dm_is_headless(adev))
+			schedule_work(&adev->dm.idle_workqueue->work);
+	}
 }
 
 void dm_helpers_dp_mst_update_branch_bandwidth(