Re: [PATCH 2/2] drm/i915/vlv: Set D3_hot for vlv during runtime_suspend

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

On Tue, 2014-06-10 at 23:05 +0530, Sagar Arun Kamble wrote:
> On Tue, 2014-06-10 at 15:43 +0300, Imre Deak wrote:
> > On Tue, 2014-06-10 at 00:27 +0530, sagar.a.kamble@intel.com wrote:
> > > From: Sagar Kamble <sagar.a.kamble@intel.com>
> > > 
> > > To do a platform wide S0i3 transition, Gfx is required to go
> > > to D3_hot state. pci_save_state and pci_restore_state needed to avoid ring
> > > hangs across D3_hot transitions.
> > > 
> > > Cc: Daniel Vetter <daniel.vetter@ffwll.ch> (supporter:INTEL DRM DRIVERS...)
> > > Cc: Jani Nikula <jani.nikula@linux.intel.com> (supporter:INTEL DRM DRIVERS...)
> > > Signed-off-by: Sagar Kamble <sagar.a.kamble@intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/i915_drv.c | 11 +++++++++++
> > >  1 file changed, 11 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> > > index 5a08c86..70bb456 100644
> > > --- a/drivers/gpu/drm/i915/i915_drv.c
> > > +++ b/drivers/gpu/drm/i915/i915_drv.c
> > > @@ -1412,6 +1412,11 @@ static int intel_runtime_suspend(struct device *device)
> > >  	 * via the suspend path.
> > >  	 */
> > >  	intel_opregion_notify_adapter(dev, PCI_D1);
> > > +	if (IS_VALLEYVIEW(dev)) {
> > > +		pci_save_state(pdev);
> > > +		pci_disable_device(pdev);
> > > +		pci_set_power_state(pdev, PCI_D3hot);
> > > +	}
> > >  
> > >  	DRM_DEBUG_KMS("Device suspended\n");
> > >  	return 0;
> > > @@ -1428,6 +1433,12 @@ static int intel_runtime_resume(struct device *device)
> > >  
> > >  	DRM_DEBUG_KMS("Resuming device\n");
> > >  
> > > +	if (IS_VALLEYVIEW(dev)) {
> > > +		pci_set_power_state(pdev, PCI_D0);
> > > +		pci_restore_state(pdev);
> > > +		pci_enable_device(pdev);
> > > +	}
> > 
> > Setting the proper Dx state and saving/restoring the PCI config space is
> > already done for us by the PCI runtime PM framework, see
> > pci_pm_runtime_suspend/resume(). 
> 
> Where exactly it calls pci_pm_set_powerstate to set D3_hot ?

It's
pci_pm_runtime_suspend()->pci_finish_runtime_suspend()->pci_set_power_state() .

> There seems to be bug in the pci driver in the suspend path. it is not
> saving the pci configuration space although code for same exists.
> pci driver checks if client driver has saved if not it will exit from
> suspend path.
> check the code snippet below:
> 
>         if (!pci_dev->state_saved && pci_dev->current_state != PCI_D0
>             && pci_dev->current_state != PCI_UNKNOWN) {
>                 WARN_ONCE(pci_dev->current_state != prev,
>                         "PCI PM: State of device not saved by %pF\n",
>                         pm->runtime_suspend);
>                 return 0;
>         }
> 
>         if (!pci_dev->state_saved) {
>                 pci_save_state(pci_dev);
>                 pci_finish_runtime_suspend(pci_dev);
>         }

I don't think this is a bug, but something the PCI framework requires
from drivers. That is if they set the power state to something else than
PCI_D0 or PCI_UNKNOWN they also have to save the state themselves.

I can't check this right now, but I haven't ever seen the above WARN and
by the look of it we are doing the right thing in the driver. That is
leave the power state in D0 and let the PCI framework handle the state
saving/power state transitioning.

--Imre