Re: [PATCH] pci/quirks: Add quirk to reset nvgpu at boot for the Lenovo ThinkPad P50

[Bjorn Helgaas <helgaas@kernel.org>]

[+cc Hans, author of 0b2fe6594fa2 ("drm/nouveau: Queue hpd_work on (runtime) resume")]

On Fri, Mar 22, 2019 at 06:30:15AM -0500, Bjorn Helgaas wrote:
> On Thu, Mar 21, 2019 at 05:48:19PM -0500, Bjorn Helgaas wrote:
> > On Wed, Mar 13, 2019 at 06:25:02PM -0400, Lyude Paul wrote:
> > > On Fri, 2019-02-15 at 16:17 -0500, Lyude Paul wrote:
> > > > On Thu, 2019-02-14 at 18:43 -0600, Bjorn Helgaas wrote:
> > > > > On Tue, Feb 12, 2019 at 05:02:30PM -0500, Lyude Paul wrote:
> > > > > > On a very specific subset of ThinkPad P50 SKUs, particularly
> > > > > > ones that come with a Quadro M1000M chip instead of the M2000M
> > > > > > variant, the BIOS seems to have a very nasty habit of not
> > > > > > always resetting the secondary Nvidia GPU between full reboots
> > > > > > if the laptop is configured in Hybrid Graphics mode. The
> > > > > > reason for this happening is unknown, but the following steps
> > > > > > and possibly a good bit of patience will reproduce the issue:
> > > > > > 
> > > > > > 1. Boot up the laptop normally in Hybrid graphics mode
> > > > > > 2. Make sure nouveau is loaded and that the GPU is awake
> > > > > > 2. Allow the nvidia GPU to runtime suspend itself after being idle
> > > > > > 3. Reboot the machine, the more sudden the better (e.g sysrq-b may help)
> > > > > > 4. If nouveau loads up properly, reboot the machine again and go back to
> > > > > > step 2 until you reproduce the issue
> > > > > > 
> > > > > > This results in some very strange behavior: the GPU will quite
> > > > > > literally be left in exactly the same state it was in when the
> > > > > > previously booted kernel started the reboot. This has all
> > > > > > sorts of bad sideaffects: for starters, this completely breaks
> > > > > > nouveau starting with a mysterious EVO channel failure that
> > > > > > happens well before we've actually used the EVO channel for
> > > > > > anything:
> > 
> > Thanks for the hybrid tutorial (snipped from this response).  IIUC,
> > what you said was that in hybrid mode, the Intel GPU drives the
> > built-in display and the Nvidia GPU drives any external displays and
> > may be used for DRI PRIME rendering (whatever that is).  But since you
> > say the Nvidia device gets runtime suspended, I assume there's no
> > external display here and you're not using DRI PRIME.
> > 
> > I wonder if it's related to the fact that the Nvidia GPU has been
> > runtime suspended before you do the reboot.  Can you try turning of
> > runtime power management for the GPU by setting the runpm module
> > parameter to 0?  I *think* this would be booting with
> > "nouveau.runpm=0".
> 
> Sorry, I wasn't really thinking here.  You already *said* this is
> related to runtime suspend.  It only happens when the Nvidia GPU has
> been suspended.
> 
> I don't know that much about suspend, but ISTR seeing comments about
> resuming devices before we shutdown.  If we do that, maybe there's
> some kind of race between that resume and the reboot?

I think we do in fact resume PCI devices before shutdown.  Here's the
path I'm looking at:

  device_shutdown
    pm_runtime_get_noresume
    pm_runtime_barrier
    dev->bus->shutdown
      pci_device_shutdown
        pm_runtime_resume
          __pm_runtime_resume(dev, 0)
            rpm_resume(dev, 0)
              __update_runtime_status(dev, RPM_RESUMING)
              callback = RPM_GET_CALLBACK(dev, runtime_resume)
              rpm_callback(callback, dev)
                __rpm_callback
                  pci_pm_runtime_resume
                    drv->pm->runtime_resume
                      nouveau_pmops_runtime_resume
                        nouveau_do_resume
                        schedule_work(hpd_work)   # <---
                        ...
                        nouveau_display_hpd_work
                          pm_runtime_get_sync
                          drm_helper_hpd_irq_event
                          pm_runtime_mark_last_busy
                          pm_runtime_put_sync

I'm curious about that "schedule_work(hpd_work)" near the end because
no other drivers seem to use schedule_work() in the runtime_resume
path, and I don't know how that synchronizes with the shutdown
process.  I don't see anything that waits for
nouveau_display_hpd_work() to complete, so it seems like something
that could be a race.

I wonder this problem would be easier to reproduce if you added a
sleep in nouveau_display_hpd_work() as in the first hunk below, and I
wonder if the problem would then go away if you stopped scheduling
hpd_work as in the second hunk?  Obviously the second hunk isn't a
solution, it's just an attempt to figure out if I'm looking in the
right area.

Bjorn


diff --git a/drivers/gpu/drm/nouveau/nouveau_display.c b/drivers/gpu/drm/nouveau/nouveau_display.c
index 55c0fa451163..e50806012d41 100644
--- a/drivers/gpu/drm/nouveau/nouveau_display.c
+++ b/drivers/gpu/drm/nouveau/nouveau_display.c
@@ -350,6 +350,7 @@ nouveau_display_hpd_work(struct work_struct *work)
 
 	pm_runtime_get_sync(drm->dev->dev);
 
+	msleep(2000);
 	drm_helper_hpd_irq_event(drm->dev);
 
 	pm_runtime_mark_last_busy(drm->dev->dev);



diff --git a/drivers/gpu/drm/nouveau/nouveau_drm.c b/drivers/gpu/drm/nouveau/nouveau_drm.c
index 5020265bfbd9..48da72caa017 100644
--- a/drivers/gpu/drm/nouveau/nouveau_drm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_drm.c
@@ -946,9 +946,6 @@ nouveau_pmops_runtime_resume(struct device *dev)
 	nvif_mask(&device->object, 0x088488, (1 << 25), (1 << 25));
 	drm_dev->switch_power_state = DRM_SWITCH_POWER_ON;
 
-	/* Monitors may have been connected / disconnected during suspend */
-	schedule_work(&nouveau_drm(drm_dev)->hpd_work);
-
 	return ret;
 }