[PATCH v4 4/8] drm/nouveau: Fix deadlock with fb_helper using new helpers

[Lyude Paul]

This removes the potential of deadlocking with fb_helper entirely by
preventing it from handling hotplugs during the runtime suspend process
as early as possible in the suspend process. If it turns out this is not
possible, due to some fb_helper action having been queued up before we
got a time to disable hotplugging, we simply return -EBUSY so that the
runtime PM core attempts autosuspending the device again once fb_helper
isn't doing anything.

This fixes one of the issues causing deadlocks on runtime suspend/resume
with nouveau on my P50.

Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Cc: Lukas Wunner <lukas@xxxxxxxxx>
Cc: Karol Herbst <karolherbst@xxxxxxxxx>
---
 drivers/gpu/drm/nouveau/nouveau_drm.c   | 8 ++++++++
 drivers/gpu/drm/nouveau/nouveau_fbcon.c | 1 +
 2 files changed, 9 insertions(+)

diff --git a/drivers/gpu/drm/nouveau/nouveau_drm.c b/drivers/gpu/drm/nouveau/nouveau_drm.c
index ee2546db09c9..d47cb5b2af98 100644
--- a/drivers/gpu/drm/nouveau/nouveau_drm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_drm.c
@@ -836,6 +836,14 @@ nouveau_pmops_runtime_suspend(struct device *dev)
 		return -EBUSY;
 	}
 
+	/* There's no way for us to stop fb_helper work in reaction to
+	 * hotplugs later in the RPM process. First off: we don't want to,
+	 * fb_helper should be able to keep the GPU awake. Second off: it is
+	 * capable of grabbing basically any lock in existence.
+	 */
+	if (!drm_fb_helper_suspend_hotplug(drm_dev->fb_helper))
+		return -EBUSY;
+
 	nouveau_switcheroo_optimus_dsm();
 	ret = nouveau_do_suspend(drm_dev, true);
 	pci_save_state(pdev);
diff --git a/drivers/gpu/drm/nouveau/nouveau_fbcon.c b/drivers/gpu/drm/nouveau/nouveau_fbcon.c
index 85c1f10bc2b6..963ba630fd04 100644
--- a/drivers/gpu/drm/nouveau/nouveau_fbcon.c
+++ b/drivers/gpu/drm/nouveau/nouveau_fbcon.c
@@ -466,6 +466,7 @@ nouveau_fbcon_set_suspend_work(struct work_struct *work)
 	console_unlock();
 
 	if (state == FBINFO_STATE_RUNNING) {
+		drm_fb_helper_resume_hotplug(drm->dev->fb_helper);
 		pm_runtime_mark_last_busy(drm->dev->dev);
 		pm_runtime_put_sync(drm->dev->dev);
 	}
-- 
2.17.1