[PATCH] drm/i915: Switch TGL-H DP-IN to dGFX when it's supported

[Kai-Heng Feng]

On Wed, Aug 17, 2022 at 2:24 AM Lyude Paul <lyude at redhat.com> wrote:
>
> On Tue, 2022-08-16 at 19:29 +0800, Kai-Heng Feng wrote:
> > On Tue, Aug 16, 2022 at 4:06 PM Jani Nikula <jani.nikula at linux.intel.com> wrote:
> > >
> > > On Tue, 16 Aug 2022, Kai-Heng Feng <kai.heng.feng at canonical.com> wrote:
> > > > On mobile workstations like HP ZBook Fury G8, iGFX's DP-IN can switch to
> > > > dGFX so external monitors are routed to dGFX, and more monitors can be
> > > > supported as result.
> > > >
> > > > To switch the DP-IN to dGFX, the driver needs to invoke _DSM function 20
> > > > on intel_dsm_guid2. This method is described in Intel document 632107.
>
> Is this documentation released anywhere? We've been wondering about these
> interfaces for quite a long time, and it would be good to know if there's docs
> for this we haven't really been seeing.
>
> > >
> > > Is this the policy decision that we want to unconditionally make,
> > > though?
> >
> > I believes so, so more external monitors can be supported at the same time.
> >
> > Kai-Heng
>
> Is this for systems with dual Intel GPUs? I ask because if this affects
> Intel/Nvidia hybrid systems then this is a huge no from me. Nouveau is able to
> support these systems, but at a limited capacity. This would imply that we are
> making external displays work for users of the nvidia proprietary driver, at
> the expense making external display support for mainline kernel users
> substantially worse for people who are using the mainline kernel. Which isn't
> a choice we should be making, because nvidia's OOT driver is not a mainline
> kernel driver.

Yes it's for Intel/NVIDIA hybrid systems.

The problem is that hardware vendor design the systems to use NVIDIA
for external displays, so using external displays on Intel are never
tested by the vendors.
I don't think that's any good either.

Kai-Heng

>
> If this is just for Intel/Intel systems though that's probably fine, and it
> might also be fine for AMD systems.
>
> >
> > >
> > > BR,
> > > Jani.
> > >
> > > >
> > > > Signed-off-by: Kai-Heng Feng <kai.heng.feng at canonical.com>
> > > > ---
> > > >  drivers/gpu/drm/i915/display/intel_acpi.c | 18 +++++++++++++++++-
> > > >  1 file changed, 17 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/gpu/drm/i915/display/intel_acpi.c b/drivers/gpu/drm/i915/display/intel_acpi.c
> > > > index e78430001f077..3bd5930e2769b 100644
> > > > --- a/drivers/gpu/drm/i915/display/intel_acpi.c
> > > > +++ b/drivers/gpu/drm/i915/display/intel_acpi.c
> > > > @@ -20,6 +20,7 @@ static const guid_t intel_dsm_guid =
> > > >                 0xa8, 0x54, 0x0f, 0x13, 0x17, 0xb0, 0x1c, 0x2c);
> > > >
> > > >  #define INTEL_DSM_FN_GET_BIOS_DATA_FUNCS_SUPPORTED 0 /* No args */
> > > > +#define INTEL_DSM_FN_DP_IN_SWITCH_TO_DGFX 20 /* No args */
> > > >
> > > >  static const guid_t intel_dsm_guid2 =
> > > >       GUID_INIT(0x3e5b41c6, 0xeb1d, 0x4260,
> > > > @@ -187,6 +188,7 @@ void intel_dsm_get_bios_data_funcs_supported(struct drm_i915_private *i915)
> > > >       struct pci_dev *pdev = to_pci_dev(i915->drm.dev);
> > > >       acpi_handle dhandle;
> > > >       union acpi_object *obj;
> > > > +     int supported = 0;
> > > >
> > > >       dhandle = ACPI_HANDLE(&pdev->dev);
> > > >       if (!dhandle)
> > > > @@ -194,8 +196,22 @@ void intel_dsm_get_bios_data_funcs_supported(struct drm_i915_private *i915)
> > > >
> > > >       obj = acpi_evaluate_dsm(dhandle, &intel_dsm_guid2, INTEL_DSM_REVISION_ID,
> > > >                               INTEL_DSM_FN_GET_BIOS_DATA_FUNCS_SUPPORTED, NULL);
> > > > -     if (obj)
> > > > +     if (obj) {
> > > > +             if (obj->type == ACPI_TYPE_INTEGER)
> > > > +                     supported = obj->integer.value;
> > > > +
> > > >               ACPI_FREE(obj);
> > > > +     }
> > > > +
> > > > +     /* Tiger Lake H DP-IN Boot Time Switching from iGfx to dGfx */
> > > > +     if (supported & BIT(20)) {
> > > > +             obj = acpi_evaluate_dsm(dhandle, &intel_dsm_guid2,
> > > > +                                     INTEL_DSM_REVISION_ID,
> > > > +                                     INTEL_DSM_FN_DP_IN_SWITCH_TO_DGFX,
> > > > +                                     NULL);
> > > > +             if (obj)
> > > > +                     ACPI_FREE(obj);
> > > > +     }
> > > >  }
> > > >
> > > >  /*
> > >
> > > --
> > > Jani Nikula, Intel Open Source Graphics Center
> >
>
> --
> Cheers,
>  Lyude Paul (she/her)
>  Software Engineer at Red Hat
>