drm/nouveau: Fix drm poll_helper handling

Commit cae9ff03 effectively disabled the drm poll_helper by checking
the wrong flag to see if the driver should enable the poll or not:
mode_config.poll_enabled is only set to true by poll_init and it is not
indicating if the poll is enabled or not.
nouveau_display_create() will initialize the poll and going to disable it
right away. After poll_init() the mode_config.poll_enabled will be true,
but the poll itself is disabled.

To avoid the race caused by calling the poll_enable() from different paths,
this patch will enable the poll from one place, in the
nouveau_display_hpd_work().

In case the pm_runtime is disabled we will enable the poll in
nouveau_drm_load() once.

Fixes: cae9ff03 ("drm/nouveau: Don't enabling polling twice on runtime resume")
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Reviewed-by: Lyude <lyude@redhat.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_display.c

@@ -360,6 +360,8 @@ nouveau_display_hpd_work(struct work_struct *work)
 	pm_runtime_get_sync(drm->dev->dev);
 
 	drm_helper_hpd_irq_event(drm->dev);
+	/* enable polling for external displays */
+	drm_kms_helper_poll_enable(drm->dev);
 
 	pm_runtime_mark_last_busy(drm->dev->dev);
 	pm_runtime_put_sync(drm->dev->dev);
@@ -413,10 +415,6 @@ nouveau_display_init(struct drm_device *dev)
 	if (ret)
 		return ret;
 
-	/* enable polling for external displays */
-	if (!dev->mode_config.poll_enabled)
-		drm_kms_helper_poll_enable(dev);
-
 	/* enable hotplug interrupts */
 	list_for_each_entry(connector, &dev->mode_config.connector_list, head) {
 		struct nouveau_connector *conn = nouveau_connector(connector);

drivers/gpu/drm/nouveau/nouveau_drm.c

@@ -502,6 +502,9 @@ nouveau_drm_load(struct drm_device *dev, unsigned long flags)
 		pm_runtime_allow(dev->dev);
 		pm_runtime_mark_last_busy(dev->dev);
 		pm_runtime_put(dev->dev);
+	} else {
+		/* enable polling for external displays */
+		drm_kms_helper_poll_enable(dev);
 	}
 	return 0;
 
@@ -774,9 +777,6 @@ nouveau_pmops_runtime_resume(struct device *dev)
 
 	ret = nouveau_do_resume(drm_dev, true);
 
-	if (!drm_dev->mode_config.poll_enabled)
-		drm_kms_helper_poll_enable(drm_dev);
-
 	/* do magic */
 	nvif_mask(&device->object, 0x088488, (1 << 25), (1 << 25));
 	vga_switcheroo_set_dynamic_switch(pdev, VGA_SWITCHEROO_ON);