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

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Date:   Wed, 24 Aug 2022 20:33:34 +0200
From:   Karol Herbst <kherbst@...hat.com>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc:     Jani Nikula <jani.nikula@...ux.intel.com>,
        tvrtko.ursulin@...ux.intel.com,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        David Airlie <airlied@...ux.ie>,
        intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org,
        Hans de Goede <hdegoede@...hat.com>, rodrigo.vivi@...el.com,
        Zenghui Yu <yuzenghui@...wei.com>
Subject: Re: [PATCH] drm/i915: Switch TGL-H DP-IN to dGFX when it's supported

On Wed, Aug 24, 2022 at 7:50 PM Kai-Heng Feng
<kai.heng.feng@...onical.com> wrote:
>
> On Tue, Aug 16, 2022 at 4:06 PM Jani Nikula <jani.nikula@...ux.intel.com> wrote:
> >
> > On Tue, 16 Aug 2022, Kai-Heng Feng <kai.heng.feng@...onical.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 the policy decision that we want to unconditionally make,
> > though?
>
> I believes so, so more external monitors can be supported at the same time.
>

if there wouldn't be any drawbacks, yes, but sadly there are and I
don't see that hurting _all_ users affected with this by making their
system consume/generate around 10-15W more power/heat just that maybe
one user can use 4 instead of 3 displays at 4K is really worth it...

> Kai-Heng
>
> >
> > BR,
> > Jani.
> >
> > >
> > > Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.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
>