Re: [PATCH 4/4] drm/nouveau/acpi: fix lockup with PCIe runtime PM

[Peter Wu <peter@lekensteyn.nl>]

On Wed, May 25, 2016 at 04:55:35PM +0300, Mika Westerberg wrote:
> On Wed, May 25, 2016 at 12:53:01AM +0200, Peter Wu wrote:
> > Since "PCI: Add runtime PM support for PCIe ports", the parent PCIe port
> > can be runtime-suspended which disables power resources via ACPI. This
> > is incompatible with DSM, resulting in a GPU device which is still in D3
> > and locks up the kernel on resume.
> > 
> > Mirror the behavior of Windows 8 and newer[1] (as observed via an AMLi
> > debugger trace) and stop using the DSM functions for D3cold when power
> > resources are available on the parent PCIe port.
> > 
> >  [1]: https://msdn.microsoft.com/windows/hardware/drivers/bringup/firmware-requirements-for-d3cold
> > 
> > Signed-off-by: Peter Wu <peter@lekensteyn.nl>
> > ---
> >  drivers/gpu/drm/nouveau/nouveau_acpi.c | 34 ++++++++++++++++++++++++++++++----
> >  1 file changed, 30 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/nouveau/nouveau_acpi.c b/drivers/gpu/drm/nouveau/nouveau_acpi.c
> > index df9f73e..e469df7 100644
> > --- a/drivers/gpu/drm/nouveau/nouveau_acpi.c
> > +++ b/drivers/gpu/drm/nouveau/nouveau_acpi.c
> > @@ -46,6 +46,7 @@ static struct nouveau_dsm_priv {
> >  	bool dsm_detected;
> >  	bool optimus_detected;
> >  	bool optimus_flags_detected;
> > +	bool optimus_skip_dsm;
> >  	acpi_handle dhandle;
> >  	acpi_handle rom_handle;
> >  } nouveau_dsm_priv;
> > @@ -212,8 +213,26 @@ static const struct vga_switcheroo_handler nouveau_dsm_handler = {
> >  	.get_client_id = nouveau_dsm_get_client_id,
> >  };
> >  
> > +/* Firmware supporting Windows 8 or later do not use _DSM to put the device into
> > + * D3cold, they instead rely on disabling power resources on the parent. */
> > +static bool nouveau_pr3_present(struct pci_dev *pdev)
> > +{
> > +	struct pci_dev *parent_pdev = pci_upstream_bridge(pdev);
> > +	struct acpi_device *ad;
> 
> Nit: please call this adev instead of ad.

Will do.

> > +
> > +	if (!parent_pdev)
> > +		return false;
> > +
> > +	ad = ACPI_COMPANION(&parent_pdev->dev);
> > +	if (!ad)
> > +		return false;
> > +
> > +	return ad->power.flags.power_resources;
> 
> Is this sufficient to tell if the parent device has _PR3? I thought it
> returns true if it has power resources in general, not necessarily _PR3.
> 
> Otherwise this looks okay to me.

It is indeed set whenever there is any _PRx method. I wonder if it is
appropriate to access fields directly like this, perhaps this would be
more accurate (based on device_pm.c):

    /* Check whether the _PR3 method is available. */
    return adev->power.states[ACPI_STATE_D3_COLD].flags.valid;

I am also considering adding a check in case the pcieport driver does
not support D3cold via runtime PM, what do you think of this?

    if (!parent_pdev)
        return false;
    /* If the PCIe port does not support D3cold via runtime PM, allow a
     * fallback to the Optimus DSM method to put the device in D3cold. */
    if (parent_pdev->no_d3cold)
        return false;

This is needed to avoid the regression reported in the cover letter, but
also allows pre-2015 systems to (still) have the D3cold possibility.


Out of curiosity I looked up an pre-2015 laptop (found Acer V5-573G,
apparently from November 2013, Windows 8.1) and extracted the ACPI
tables from the BIOS images. BIOS 2.28 (2014/05/13) introduces support
for power resources on the parent devicea(\_SB.PCI0.PEG0._PR3 and a
related NVP3 device) when _OSI("Windows 2013") is true. (This is added
as alternative for the old DSM interface.)

Maybe 2014 is also an appropriate cutoff date? I wonder if it is
feasible to detect firmware use of _OSI("Windows 2013") and use that
instead of the BIOS year.
-- 
Kind regards,
Peter Wu
https://lekensteyn.nl