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

[Kai-Heng Feng <kai.heng.feng@canonical.com>]

On Wed, Aug 17, 2022 at 2:36 AM Lyude Paul <lyude@redhat.com> wrote:
>
> On Tue, 2022-08-16 at 14:24 -0400, Lyude Paul 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@linux.intel.com> wrote:
> > > >
> > > > On Tue, 16 Aug 2022, Kai-Heng Feng <kai.heng.feng@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.
>
> Doing some quick research, unless the models mentioned in the commit message
> are unreleased some of them are definitely Intel/Nvidia hybrids. So I'm going
> to say:
>
> NAK-by: Lyude Paul <lyude@redhat.com>
>
> If you'd like to resubmit this for systems with amdgpus and Intel only, that's
> perfectly fine with me if the Intel folks are ok with it. But please hold off
> on this for Nvidia systems, at least until we've got GSP reworks functional in
> nouveau. If nvidia's interested in making this work for their driver, they're
> welcome to do the work there. For reference: the main limitations you would
> hit as a result of this patch would be lagginess on the external displays as a
> result of us not being able to reclock the GPU, which means PCIe bandwidth
> will be pretty limited.

The change should be agnostic to any discrete GPU, so I don't think
it's easy to make i915 be aware of the presence of AMD or NVIDIA.
As I replied in previous mail, the external displays may not even work
on Intel GPU, so I really hope we can get this merged.

Will the 'GSP rework' finish anytime soon?

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@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
>