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

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, Apr 18, 2016 at 11:54:31AM +0300, Imre Deak wrote:
> On ma, 2016-04-18 at 11:44 +0300, Ville Syrj�l� wrote:
> > On Mon, Apr 18, 2016 at 11:32:38AM +0300, Imre Deak wrote:
> > > On ma, 2016-04-18 at 11:28 +0300, Ville Syrj�l� 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 Syrj�l� <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.

Yeah, was thinking that we could assert that we're in D0, required BARs,
BM, pci int/msi etc. are enabled.

-- 
Ville Syrj�l�
Intel OTC