[PATCH v2] drm/amdgpu: Disable RPM helpers while reprobing connectors on resume

From: Lyude
Date: Mon Jul 18 2016 - 11:42:09 EST

Just about all of amdgpu's connector probing functions try to acquire
runtime PM refs. If we try to do this in the context of
amdgpu_resume_kms by calling drm_helper_hpd_irq_event(), we end up
deadlocking the system.

Since we're guaranteed to be holding the spinlock for RPM in
amdgpu_resume_kms, and we already know the GPU is in working order, we
need to prevent the RPM helpers from trying to run during the initial
connector reprobe on resume.

There's a couple of solutions I've explored for fixing this, but this
one by far seems to be the simplest and most reliable (plus I'm pretty
sure that's what disable_depth is there for anyway).

Reproduction recipe:
- Get any laptop dual GPUs using PRIME
- Make sure runtime PM is enabled for amdgpu
- Boot the machine
- If the machine managed to boot without hanging, switch out of X to
another VT. This should definitely cause X to hang infinitely.

Changes since v1:
- add appropriate #ifdef checks for CONFIG_PM. This is not very
useful, but it appears some kernel test suites test compiling amdgpu
with CONFIG_PM disabled, which results in this patch breaking the builds
if we don't include this #ifdef

Cc: stable@xxxxxxxxxxxxxxx
Cc: Alex Deucher <alexdeucher@xxxxxxxxx>
Signed-off-by: Lyude <cpaul@xxxxxxxxxx>
drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
index 6e92008..b7f5650 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
@@ -1841,7 +1841,23 @@ int amdgpu_resume_kms(struct drm_device *dev, bool resume, bool fbcon)

+ /*
+ * Most of the connector probing functions try to acquire runtime pm
+ * refs to ensure that the GPU is powered on when connector polling is
+ * performed. Since we're calling this from a runtime PM callback,
+ * trying to acquire rpm refs will cause us to deadlock.
+ *
+ * Since we're guaranteed to be holding the rpm lock, it's safe to
+ * temporarily disable the rpm helpers so this doesn't deadlock us.
+ */
+#ifdef CONFIG_PM
+ dev->dev->power.disable_depth++;
+#ifdef CONFIG_PM
+ dev->dev->power.disable_depth--;

if (fbcon) {
amdgpu_fbdev_set_suspend(adev, 0);