Re: Panic after S3 resume and modeset with MST

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On Mon, 27 Mar 2017 18:02:13 +0200,
Takashi Iwai wrote:
> 
> Hi,
> 
> the upstream fix a16b7658f4e0d4aec9bc3e75a5f0cc3f7a3a0422
>     drm/i915: Call intel_dp_mst_resume() before resuming displays
> 
> seems to trigger a kernel panic when some modeset change happens after
> S3 resume.  The details are found in openSUSE bugzilla,
>   https://bugzilla.suse.com/show_bug.cgi?id=1029634
> 
> In short, the following procedure causes a kernel panic (supposedly)
> almost 100% on Dell Latitude with Skylake with MST DP on dock:
> 
> - Boot with a docking station, DP-1 connected.
> - Login on X
> - xrandr --output eDP-1 --primary --auto --output DP-1-1 --auto --left-of eDP-1
>   ==> This changes the mode.
> - Suspend ("systemctl suspend" in my case), and close the lid.
> - Remove from the dock (keep the lid closed).
> - Open the lid, which resumes automatically.  It works.
> - Suspend again.
> - Connect to the dock again (keep the lid closed).
> - Open the lid, which resumes automatically.  It's still OK.
> - xrandr --output eDP-1 --primary --auto --output DP-1-1 --auto --left-of eDP-1
>   ==> Now the kernel feezes.
> 
> Reverting the commit mentioned above fixes the problem.
> 
> The problem is present in all versions I tested.  The reported kernel
> in the Bugzilla is 4.4.x-based one, but the issue is seen in 4.11-rc3,
> too.  Note that the S3 resume itself works in 4.11-rc3; the kernel
> panic happens when invoking xrandr manually after that.
> 
> Unfortunately, I couldn't get a kernel panic message, so far.  kdump
> didn't work well in this case by some reason.  There are some
> screenshots taken by the original reporter (could switch VT
> beforehand), but I don't know whether it helps.
> 
> If you have any hints for further debugging, it'd be highly
> appreciated.

It seems that the patch below works around the problem.
Can anyone enlighten what's going on there?


thanks,

Takashi

-- 8< --
From: Takashi Iwai <tiwai@xxxxxxx>
Subject: [PATCH] drm/i915: Fix crash after S3 resume with DP MST mode change

We've got a bug report showing that Skylake Dell machines with a
docking station causes a kernel panic after S3 resume and modeset.
The details are found in the openSUSE bugzilla entry below.  The
typical test procedure is:

- Laptop is Dell Latitude with eDP (1366x768)
- Boot with docking station connected to a DP (1920x1080)
- Login, change the mode via
  xrandr --output eDP-1 --auto --output DP-1-1 --auto --left-of eDP-1
- Suspend, and close the lid after the suspend
  (or close the lid to trigger the suspend)
- Undock while keeping the lid closed.
- Open the lid, which triggers the resume;
  the machine wakes up well, and X shows up.  No problem, so far.
- Suspend again, close the lid.
- Dock again while keeping the lid closed.
- Open the lid, triggering the resume; this wakes up still fine.
- At this moment, run xrandr again to re-setup DP-1
  xrandr --output eDP-1 --auto --output DP-1-1 --auto --left-of eDP-1
  ==> This triggers a hard crash.

I could bisect it, and this leaded to the commit a16b7658f4e0
("drm/i915: Call intel_dp_mst_resume() before resuming displays").

Basically the commit just shuffles the calls of intel_display_resume()
and intel_dp_mst_resume().  So as a workaround, I tried to split
intel_dp_mst_resume() call to postpone the suspected code (the
invocation of intel_dp_check_mst_status()), then bingo, this cured the
problem.

But don't ask me *why* this fixes.  It's still in a cargo-cult state.

Fixes: a16b7658f4e0 ("drm/i915: Call intel_dp_mst_resume() before resuming displays")
Bugzilla: https://bugzilla.suse.com/show_bug.cgi?id=1029634
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
---
 drivers/gpu/drm/i915/i915_drv.c  |  5 ++++-
 drivers/gpu/drm/i915/intel_dp.c  | 20 +++++++++++++++++++-
 drivers/gpu/drm/i915/intel_drv.h |  3 ++-
 3 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 1c75402a59c1..62c40090ceed 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -1559,6 +1559,7 @@ static int i915_suspend_switcheroo(struct drm_device *dev, pm_message_t state)
 static int i915_drm_resume(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = to_i915(dev);
+	int mst_pending;
 	int ret;
 
 	disable_rpm_wakeref_asserts(dev_priv);
@@ -1608,10 +1609,12 @@ static int i915_drm_resume(struct drm_device *dev)
 		dev_priv->display.hpd_irq_setup(dev_priv);
 	spin_unlock_irq(&dev_priv->irq_lock);
 
-	intel_dp_mst_resume(dev);
+	mst_pending = intel_dp_mst_resume(dev);
 
 	intel_display_resume(dev);
 
+	intel_dp_mst_resume_post(dev, mst_pending);
+
 	drm_kms_helper_poll_enable(dev);
 
 	/*
diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index d1670b8afbf5..fc5ea900e6f3 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -6027,9 +6027,10 @@ void intel_dp_mst_suspend(struct drm_device *dev)
 	}
 }
 
-void intel_dp_mst_resume(struct drm_device *dev)
+int intel_dp_mst_resume(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = to_i915(dev);
+	int pending = 0;
 	int i;
 
 	for (i = 0; i < I915_MAX_PORTS; i++) {
@@ -6041,6 +6042,23 @@ void intel_dp_mst_resume(struct drm_device *dev)
 
 		ret = drm_dp_mst_topology_mgr_resume(&intel_dig_port->dp.mst_mgr);
 		if (ret)
+			pending |= 1 << i;
+	}
+
+	return pending;
+}
+
+void intel_dp_mst_resume_post(struct drm_device *dev, int pending)
+{
+	struct drm_i915_private *dev_priv = to_i915(dev);
+	int i;
+
+	for (i = 0; i < I915_MAX_PORTS; i++) {
+		struct intel_digital_port *intel_dig_port =
+			dev_priv->hotplug.irq_port[i];
+		if (!intel_dig_port || !intel_dig_port->dp.can_mst)
+			continue;
+		if (pending & (1 << i))
 			intel_dp_check_mst_status(&intel_dig_port->dp);
 	}
 }
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 344f238b283f..2025aafdcd26 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -1447,7 +1447,8 @@ void intel_edp_panel_on(struct intel_dp *intel_dp);
 void intel_edp_panel_off(struct intel_dp *intel_dp);
 void intel_dp_add_properties(struct intel_dp *intel_dp, struct drm_connector *connector);
 void intel_dp_mst_suspend(struct drm_device *dev);
-void intel_dp_mst_resume(struct drm_device *dev);
+int intel_dp_mst_resume(struct drm_device *dev);
+void intel_dp_mst_resume_post(struct drm_device *dev, int pending);
 int intel_dp_max_link_rate(struct intel_dp *intel_dp);
 int intel_dp_rate_select(struct intel_dp *intel_dp, int rate);
 void intel_dp_hot_plug(struct intel_encoder *intel_encoder);
-- 
2.11.1

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