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

Chris Wilson
2016-04-18T08:24:40Z

On Mon, Apr 18, 2016 at 11:16:34AM +0300, Imre Deak wrote:
> On ma, 2016-04-18 at 09:06 +0100, Chris Wilson 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;
> > > + }
> >
> > The device should be enabled first, otherwise we are not meant to be
> > touching its IO space at all (such as twiddling power state). At
> > least
> > that is the order pci_enable_device() uses.
>
> It's not MMIO or (port) IO but only a PCI config space access
> that pci_set_power_state() requires, so doesn't need the enabling
> of PCI resources. AFAICS pci_enable_device() enables power as the first
> thing.
>
> > Either way, upon failure we should be unwinding.
>
> I'd rather wouldn't put back the device to D3 state, as further device
> access may still possible even though resume failed.

On the other hand, if you order it thusly:

if (!pci_enable_device())
return -EIO;

ret = pci_set_power_state()
if (ret < 0) {
pci_disable_device()
return ret;
}

it doesn't raise as many eyebrows :)
-Chris

--
Chris Wilson, Intel Open Source Technology Centre