[PATCH] drm/nouveau: Don't enabling polling twice on runtime resume

[Lyude]

As it turns out, on cards that actually have CRTCs on them we're already
calling drm_kms_helper_poll_enable(drm_dev) from
nouveau_display_resume() before we call it in
nouveau_pmops_runtime_resume(). This leads us to accidentally trying to
enable polling twice, which results in a potential deadlock between the
RPM locks and drm_dev->mode_config.mutex if we end up trying to enable
polling the second time while output_poll_execute is running and holding
the mode_config lock. As such, make sure we only enable polling in
nouveau_pmops_runtime_resume() if we need to.

This fixes hangs observed on the ThinkPad W541

Signed-off-by: Lyude <lyude@xxxxxxxxxx>
---
It should be noted this issue only started recently, and it doesn't look like
this code has been touched that recently. So there might already be something
else going on here that's suddenly causing this to be a bug.

 drivers/gpu/drm/nouveau/nouveau_drm.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_drm.c b/drivers/gpu/drm/nouveau/nouveau_drm.c
index 3100fd88..35ffa41 100644
--- a/drivers/gpu/drm/nouveau/nouveau_drm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_drm.c
@@ -761,7 +761,14 @@ nouveau_pmops_runtime_resume(struct device *dev)
 	pci_set_master(pdev);
 
 	ret = nouveau_do_resume(drm_dev, true);
-	drm_kms_helper_poll_enable(drm_dev);
+
+	/* If this card has CRTCs attached to it, nouveau_do_resume() will have
+	 * already enabled polling. As such, make sure we don't enable it twice
+	 * and deadlock
+	 */
+	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);
-- 
2.7.4