Date:	Wed, 9 Mar 2016 21:17:50 +0100
From:	Lukas Wunner <lukas@...ner.de>
To:	Alex Deucher <alexdeucher@...il.com>
Cc:	Dave Airlie <airlied@...il.com>,
	Linux ACPI <linux-acpi@...r.kernel.org>,
	Linux PCI <linux-pci@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Maling list - DRI developers 
	<dri-devel@...ts.freedesktop.org>, linux-pm@...r.kernel.org
Subject: Re: [PATCH 1/2] vga_switcheroo: add power support for windows 10
 machines.

Hi,

On Wed, Mar 09, 2016 at 11:52:33AM -0500, Alex Deucher wrote:
> On Wed, Mar 9, 2016 at 9:33 AM, Lukas Wunner <lukas@...ner.de> wrote:
> > On Wed, Mar 09, 2016 at 04:14:04PM +1000, Dave Airlie wrote:
> >> From: Dave Airlie <airlied@...hat.com>
> >>
> >> Windows 10 seems to have standardised power control for the
> >> optimus/powerxpress laptops using PR3 power resource hooks.
> >
> > What happened to the Optimus DSM, does this still work? If not,
> > echoing OFF to the vgaswitcheroo sysfs file won't power down the
> > GPU now, right? (If runtime pm is disabled in nouveau.)
> >
> If the OS identifies itself as windows 10 or newer when initializing
> ACPI, the standardized interfaces should be used if they exist.  I'm
> not sure if there is any explicit policy on the vendor specific ones,
> but I suspect they are probably broken in that case since I doubt the
> OEM validates them when the standardized interfaces are available.

The vendor interface (Optimus DSM) must be present, otherwise the call
to nouveau_is_optimus() in patch [2/2] would return false.

But indeed it seems to not be working, otherwise why would the patches
be necessary?

My point is that the chosen approach does not square with vga_switcheroo's
architecture: Normally it's the handler's job to power the GPU up/down.
If runtime pm is enabled then vga_switcheroo_init_domain_pm_ops()
activates runtime_suspend/_resume callbacks which ask the handler to
flip the power switch.

However these two patches add *additional* runtime_suspend/_resume
callbacks which do not rely on the handler at all. The handler is thus
useless. This becomes apparent when loading the nouveau module with
runpm=0: Normally the user is then able to manually power the GPU
up/down by echoing ON or OFF to the vgaswitcheroo sysfs file. With the
chosen approach this will likely not work because the handler only knows
how to invoke the DSM, it doesn't know anything about PR3.

Hence my suggestion to solve this with an additional handler which
gets used in lieu of the nouveau DSM handler.

Best regards,

Lukas

> 
> Alex
> 
> >> I'm not sure this is definitely the correct place to be
> >> doing this, but it works for me here.
> >
> > How about implementing an additional vga_switcheroo handler somewhere
> > in drivers/acpi/, which looks for the PR3 hooks and registers with
> > vga_switcheroo if found. The ->power_state callback of that handler
> > would then invoke acpi_device_set_power().
> >
> > The ACPI bus is scanned in the subsys_initcall section, much earlier
> > than nouveau is loaded (in the device_initcall section). So the ACPI
> > vga_switcheroo handler could register before the nouveau DSM handler
> > and therefore would always have a higher precedence.
> >
> > In any case this patch should be amended with kerneldoc for
> > vga_switcheroo_init_parent_pr3_ops(), I've spent considerable time
> > last year to document everything and kindly ask that this water not
> > be muddied again. ;-)
> >
> > One small nit, the headers are sorted alphabetically yet acpi.h is
> > added at the end.
> >
> > Thanks,
> >
> > Lukas
> >
> >>
> >> The ACPI device for the GPU I have is \_SB_.PCI0.PEG_.VID_
> >> but the power resource hooks are on \_SB_.PCI0.PEG_, so
> >> this patch creates a new power domain to turn the GPU
> >> device parent off using standard ACPI calls.
> >>
> >> Signed-off-by: Dave Airlie <airlied@...hat.com>
> >> ---
> >>  drivers/gpu/vga/vga_switcheroo.c | 54 +++++++++++++++++++++++++++++++++++++++-
> >>  include/linux/vga_switcheroo.h   |  3 ++-
> >>  2 files changed, 55 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/gpu/vga/vga_switcheroo.c b/drivers/gpu/vga/vga_switcheroo.c
> >> index 665ab9f..be32cb2 100644
> >> --- a/drivers/gpu/vga/vga_switcheroo.c
> >> +++ b/drivers/gpu/vga/vga_switcheroo.c
> >> @@ -42,7 +42,7 @@
> >>  #include <linux/uaccess.h>
> >>  #include <linux/vgaarb.h>
> >>  #include <linux/vga_switcheroo.h>
> >> -
> >> +#include <linux/acpi.h>
> >>  /**
> >>   * DOC: Overview
> >>   *
> >> @@ -997,3 +997,55 @@ vga_switcheroo_init_domain_pm_optimus_hdmi_audio(struct device *dev,
> >>       return -EINVAL;
> >>  }
> >>  EXPORT_SYMBOL(vga_switcheroo_init_domain_pm_optimus_hdmi_audio);
> >> +
> >> +/* With Windows 10 the runtime suspend/resume can use power
> >> +   resources on the parent device */
> >> +static int vga_acpi_switcheroo_runtime_suspend(struct device *dev)
> >> +{
> >> +     struct pci_dev *pdev = to_pci_dev(dev);
> >> +     int ret;
> >> +     struct acpi_device *adev;
> >> +
> >> +     ret = dev->bus->pm->runtime_suspend(dev);
> >> +     if (ret)
> >> +             return ret;
> >> +
> >> +     ret = acpi_bus_get_device(ACPI_HANDLE(&pdev->dev), &adev);
> >> +     if (!ret)
> >> +             acpi_device_set_power(adev->parent, ACPI_STATE_D3_COLD);
> >> +     return 0;
> >> +}
> >> +
> >> +static int vga_acpi_switcheroo_runtime_resume(struct device *dev)
> >> +{
> >> +     struct pci_dev *pdev = to_pci_dev(dev);
> >> +     struct acpi_device *adev;
> >> +     int ret;
> >> +
> >> +     ret = acpi_bus_get_device(ACPI_HANDLE(&pdev->dev), &adev);
> >> +     if (!ret)
> >> +             acpi_device_set_power(adev->parent, ACPI_STATE_D0);
> >> +     ret = dev->bus->pm->runtime_resume(dev);
> >> +     if (ret)
> >> +             return ret;
> >> +
> >> +     return 0;
> >> +}
> >> +
> >> +int vga_switcheroo_init_parent_pr3_ops(struct device *dev,
> >> +                                    struct dev_pm_domain *domain)
> >> +
> >> +{
> >> +     /* copy over all the bus versions */
> >> +     if (dev->bus && dev->bus->pm) {
> >> +             domain->ops = *dev->bus->pm;
> >> +             domain->ops.runtime_suspend = vga_acpi_switcheroo_runtime_suspend;
> >> +             domain->ops.runtime_resume = vga_acpi_switcheroo_runtime_resume;
> >> +
> >> +             dev_pm_domain_set(dev, domain);
> >> +             return 0;
> >> +     }
> >> +     dev_pm_domain_set(dev, NULL);
> >> +     return -EINVAL;
> >> +}
> >> +EXPORT_SYMBOL(vga_switcheroo_init_parent_pr3_ops);
> >> diff --git a/include/linux/vga_switcheroo.h b/include/linux/vga_switcheroo.h
> >> index 69e1d4a1..5ce0cbe 100644
> >> --- a/include/linux/vga_switcheroo.h
> >> +++ b/include/linux/vga_switcheroo.h
> >> @@ -144,6 +144,7 @@ void vga_switcheroo_set_dynamic_switch(struct pci_dev *pdev, enum vga_switcheroo
> >>  int vga_switcheroo_init_domain_pm_ops(struct device *dev, struct dev_pm_domain *domain);
> >>  void vga_switcheroo_fini_domain_pm_ops(struct device *dev);
> >>  int vga_switcheroo_init_domain_pm_optimus_hdmi_audio(struct device *dev, struct dev_pm_domain *domain);
> >> +int vga_switcheroo_init_parent_pr3_ops(struct device *dev, struct dev_pm_domain *domain);
> >>  #else
> >>
> >>  static inline void vga_switcheroo_unregister_client(struct pci_dev *dev) {}
> >> @@ -163,6 +164,6 @@ static inline void vga_switcheroo_set_dynamic_switch(struct pci_dev *pdev, enum
> >>  static inline int vga_switcheroo_init_domain_pm_ops(struct device *dev, struct dev_pm_domain *domain) { return -EINVAL; }
> >>  static inline void vga_switcheroo_fini_domain_pm_ops(struct device *dev) {}
> >>  static inline int vga_switcheroo_init_domain_pm_optimus_hdmi_audio(struct device *dev, struct dev_pm_domain *domain) { return -EINVAL; }
> >> -
> >> +static inline int vga_switcheroo_init_parent_pr3_ops(struct device *dev, struct dev_pm_domain *domain) { return -EINVAL; }
> >>  #endif
> >>  #endif /* _LINUX_VGA_SWITCHEROO_H_ */
> >> --
> >> 2.5.0

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