drm/nouveau: Handle fbcon suspend/resume in seperate worker

Resuming from RPM can happen while already holding
dev->mode_config.mutex. This means we can't actually handle fbcon in
any RPM resume workers, since restoring fbcon requires grabbing
dev->mode_config.mutex again. So move the fbcon suspend/resume code into
it's own worker, and rely on that instead to avoid deadlocking.

This fixes more deadlocks for runtime suspending the GPU on the ThinkPad
W541. Reproduction recipe:

 - Get a machine with both optimus and a nvidia card with connectors
   attached to it
 - Wait for the nvidia GPU to suspend
 - Attempt to manually reprobe any of the connectors on the nvidia GPU
   using sysfs
 - *deadlock*

[airlied: use READ_ONCE to address Hans's comment]
Signed-off-by: Lyude <lyude@redhat.com>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Kilian Singer <kilian.singer@quantumtechnology.info>
Cc: Lukas Wunner <lukas@wunner.de>
Cc: David Airlie <airlied@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/nouveau/nouveau_drv.h

@@ -165,6 +165,8 @@ struct nouveau_drm {
 	struct backlight_device *backlight;
 	struct list_head bl_connectors;
 	struct work_struct hpd_work;
+	struct work_struct fbcon_work;
+	int fbcon_new_state;
 #ifdef CONFIG_ACPI
 	struct notifier_block acpi_nb;
 #endif

drivers/gpu/drm/nouveau/nouveau_fbcon.c

@@ -470,19 +470,43 @@ static const struct drm_fb_helper_funcs nouveau_fbcon_helper_funcs = {
 	.fb_probe = nouveau_fbcon_create,
 };
 
+static void
+nouveau_fbcon_set_suspend_work(struct work_struct *work)
+{
+	struct nouveau_drm *drm = container_of(work, typeof(*drm), fbcon_work);
+	int state = READ_ONCE(drm->fbcon_new_state);
+
+	if (state == FBINFO_STATE_RUNNING)
+		pm_runtime_get_sync(drm->dev->dev);
+
+	console_lock();
+	if (state == FBINFO_STATE_RUNNING)
+		nouveau_fbcon_accel_restore(drm->dev);
+	drm_fb_helper_set_suspend(&drm->fbcon->helper, state);
+	if (state != FBINFO_STATE_RUNNING)
+		nouveau_fbcon_accel_save_disable(drm->dev);
+	console_unlock();
+
+	if (state == FBINFO_STATE_RUNNING) {
+		pm_runtime_mark_last_busy(drm->dev->dev);
+		pm_runtime_put_sync(drm->dev->dev);
+	}
+}
+
 void
 nouveau_fbcon_set_suspend(struct drm_device *dev, int state)
 {
 	struct nouveau_drm *drm = nouveau_drm(dev);
-	if (drm->fbcon) {
-		console_lock();
-		if (state == FBINFO_STATE_RUNNING)
-			nouveau_fbcon_accel_restore(dev);
-		drm_fb_helper_set_suspend(&drm->fbcon->helper, state);
-		if (state != FBINFO_STATE_RUNNING)
-			nouveau_fbcon_accel_save_disable(dev);
-		console_unlock();
-	}
+
+	if (!drm->fbcon)
+		return;
+
+	drm->fbcon_new_state = state;
+	/* Since runtime resume can happen as a result of a sysfs operation,
+	 * it's possible we already have the console locked. So handle fbcon
+	 * init/deinit from a seperate work thread
+	 */
+	schedule_work(&drm->fbcon_work);
 }
 
 int
@@ -502,6 +526,7 @@ nouveau_fbcon_init(struct drm_device *dev)
 		return -ENOMEM;
 
 	drm->fbcon = fbcon;
+	INIT_WORK(&drm->fbcon_work, nouveau_fbcon_set_suspend_work);
 
 	drm_fb_helper_prepare(dev, &fbcon->helper, &nouveau_fbcon_helper_funcs);