Re: [PATCH 2/4] drm/i915: Fix system resume if PCI device remained enabled

[Imre Deak <imre.deak@intel.com>]

On ma, 2016-04-18 at 11:44 +0300, Ville Syrjälä wrote:
> On Mon, Apr 18, 2016 at 11:32:38AM +0300, Imre Deak wrote:
> > On ma, 2016-04-18 at 11:28 +0300, Ville Syrjälä wrote:
> > > On Mon, Apr 18, 2016 at 10:04:20AM +0300, Imre Deak wrote:
> > > > During system resume we depended on pci_enable_device() also
> > > > putting the
> > > > device into PCI D0 state. This won't work if the PCI device was
> > > > already
> > > > enabled but still in D3 state. This is because pci_enable_device()
> > > > is
> > > > refcounted and will not change the HW state if called with a non-
> > > > zero
> > > > refcount. Leaving the device in D3 will make all subsequent device
> > > > accesses fail.
> > > > 
> > > > This didn't cause a problem most of the time, since we resumed with
> > > > an
> > > > enable refcount of 0. But it fails at least after module reload
> > > > because
> > > > after that we also happen to leak a PCI device enable reference:
> > > > During
> > > > probing we call drm_get_pci_dev() which will enable the PCI device,
> > > > but
> > > > during device removal drm_put_dev() won't disable it. This is a bug
> > > > of
> > > > its own in DRM core, but without much harm as it only leaves the
> > > > PCI
> > > > device enabled. Fixing it is also a bit more involved, due to DRM
> > > > mid-layering and because it affects non-i915 drivers too. The fix
> > > > in
> > > > this patch is valid regardless of the problem in DRM core.
> > > > 
> > > > CC: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > > CC: stable@vger.kernel.org
> > > > Signed-off-by: Imre Deak <imre.deak@intel.com>
> > > > ---
> > > >  drivers/gpu/drm/i915/i915_drv.c | 9 ++++++++-
> > > >  1 file changed, 8 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/i915/i915_drv.c
> > > > b/drivers/gpu/drm/i915/i915_drv.c
> > > > index d550ae2..7eaa93e 100644
> > > > --- a/drivers/gpu/drm/i915/i915_drv.c
> > > > +++ b/drivers/gpu/drm/i915/i915_drv.c
> > > > @@ -803,7 +803,7 @@ static int i915_drm_resume(struct drm_device
> > > > *dev)
> > > >  static int i915_drm_resume_early(struct drm_device *dev)
> > > >  {
> > > >  	struct drm_i915_private *dev_priv = dev->dev_private;
> > > > -	int ret = 0;
> > > > +	int ret;
> > > >  
> > > >  	/*
> > > >  	 * We have a resume ordering issue with the snd-hda driver
> > > > also
> > > > @@ -814,6 +814,13 @@ static int i915_drm_resume_early(struct
> > > > drm_device *dev)
> > > >  	 * FIXME: This should be solved with a special hdmi sink
> > > > device or
> > > >  	 * similar so that power domains can be employed.
> > > >  	 */
> > > > +
> > > > +	ret = pci_set_power_state(dev->pdev, PCI_D0);
> > > > +	if (ret) {
> > > > +		DRM_ERROR("failed to set PCI D0 power state
> > > > (%d)\n", ret);
> > > > +		goto out;
> > > > +	}
> > > 
> > > Hmm. Doesn't this already happen from pci bus resume_noirq hook?
> > 
> > It does, but not during thaw_noirq.
> 
> Maybe put that into a comment? If we ever get to dropping the device
> state frobbery from freeze/thaw, then we should also be able to throw
> out the pci_set_power_state() call as well.

Yes, can add a comment.

> Perhaps we should have some asserts about the state of the PCI device?

You mean after calling pci_enable_device() that it's indeed in D0 and
enabled? Can do that as a follow-up.

--Imre