[PATCH v2] ACPI: Fix selecting the wrong ACPI fwnode for the iGPU on some Dell laptops

[Rafael J. Wysocki]

On Wed, Jan 11, 2023 at 9:23 PM Hans de Goede <hdegoede at redhat.com> wrote:
>
> Hi,
>
> On 1/11/23 21:16, Rafael J. Wysocki wrote:
> > On Tue, Jan 10, 2023 at 4:30 PM Hans de Goede <hdegoede at redhat.com> wrote:
> >>
> >> The Dell Latitude E6430 both with and without the optional NVidia dGPU
> >> has a bug in its ACPI tables which is causing Linux to assign the wrong
> >> ACPI fwnode / companion to the pci_device for the i915 iGPU.
> >>
> >> Specifically under the PCI root bridge there are these 2 ACPI Device()s :
> >>
> >>  Scope (_SB.PCI0)
> >>  {
> >>      Device (GFX0)
> >>      {
> >>          Name (_ADR, 0x00020000)  // _ADR: Address
> >>      }
> >>
> >>      ...
> >>
> >>      Device (VID)
> >>      {
> >>          Name (_ADR, 0x00020000)  // _ADR: Address
> >>          ...
> >>
> >>          Method (_DOS, 1, NotSerialized)  // _DOS: Disable Output Switching
> >>          {
> >>              VDP8 = Arg0
> >>              VDP1 (One, VDP8)
> >>          }
> >>
> >>          Method (_DOD, 0, NotSerialized)  // _DOD: Display Output Devices
> >>          {
> >>              ...
> >>          }
> >>          ...
> >>      }
> >>  }
> >>
> >> The non-functional GFX0 ACPI device is a problem, because this gets
> >> returned as ACPI companion-device by acpi_find_child_device() for the iGPU.
> >>
> >> This is a long standing problem and the i915 driver does use the ACPI
> >> companion for some things, but works fine without it.
> >>
> >> However since commit 63f534b8bad9 ("ACPI: PCI: Rework acpi_get_pci_dev()")
> >> acpi_get_pci_dev() relies on the physical-node pointer in the acpi_device
> >> and that is set on the wrong acpi_device because of the wrong
> >> acpi_find_child_device() return. This breaks the ACPI video code,
> >> leading to non working backlight control in some cases.
> >>
> >> Add a type.backlight flag, mark ACPI video bus devices with this and make
> >> find_child_checks() return a higher score for children with this flag set,
> >> so that it picks the right companion-device.
> >>
> >> Co-developed-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
> >> Signed-off-by: Hans de Goede <hdegoede at redhat.com>
> >> ---
> >> Changes in v2:
> >> - Switch to Rafael's suggested implementation using a type.backlight flag
> >>   and only make find_child_checks() return a higher score when this is set
> >> ---
> >>  drivers/acpi/glue.c     | 14 ++++++++++++--
> >>  drivers/acpi/scan.c     |  7 +++++--
> >>  include/acpi/acpi_bus.h |  3 ++-
> >>  3 files changed, 19 insertions(+), 5 deletions(-)
> >>
> >> diff --git a/drivers/acpi/glue.c b/drivers/acpi/glue.c
> >> index 204fe94c7e45..a194f30876c5 100644
> >> --- a/drivers/acpi/glue.c
> >> +++ b/drivers/acpi/glue.c
> >> @@ -75,7 +75,8 @@ static struct acpi_bus_type *acpi_get_bus_type(struct device *dev)
> >>  }
> >>
> >>  #define FIND_CHILD_MIN_SCORE   1
> >> -#define FIND_CHILD_MAX_SCORE   2
> >> +#define FIND_CHILD_MID_SCORE   2
> >> +#define FIND_CHILD_MAX_SCORE   3
> >>
> >>  static int match_any(struct acpi_device *adev, void *not_used)
> >>  {
> >> @@ -96,8 +97,17 @@ static int find_child_checks(struct acpi_device *adev, bool check_children)
> >>                 return -ENODEV;
> >>
> >>         status = acpi_evaluate_integer(adev->handle, "_STA", NULL, &sta);
> >> -       if (status == AE_NOT_FOUND)
> >> +       if (status == AE_NOT_FOUND) {
> >> +               /*
> >> +                * Special case: backlight device objects without _STA are
> >> +                * preferred to other objects with the same _ADR value, because
> >> +                * it is more likely that they are actually useful.
> >> +                */
> >> +               if (adev->pnp.type.backlight)
> >> +                       return FIND_CHILD_MID_SCORE;
> >> +
> >>                 return FIND_CHILD_MIN_SCORE;
> >> +       }
> >>
> >>         if (ACPI_FAILURE(status) || !(sta & ACPI_STA_DEVICE_ENABLED))
> >>                 return -ENODEV;
> >> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> >> index 274344434282..0c6f06abe3f4 100644
> >> --- a/drivers/acpi/scan.c
> >> +++ b/drivers/acpi/scan.c
> >> @@ -1370,9 +1370,12 @@ static void acpi_set_pnp_ids(acpi_handle handle, struct acpi_device_pnp *pnp,
> >>                  * Some devices don't reliably have _HIDs & _CIDs, so add
> >>                  * synthetic HIDs to make sure drivers can find them.
> >>                  */
> >> -               if (acpi_is_video_device(handle))
> >> +               if (acpi_is_video_device(handle)) {
> >>                         acpi_add_id(pnp, ACPI_VIDEO_HID);
> >> -               else if (acpi_bay_match(handle))
> >> +                       pnp->type.backlight = 1;
> >> +                       break;
> >> +               }
> >> +               if (acpi_bay_match(handle))
> >>                         acpi_add_id(pnp, ACPI_BAY_HID);
> >>                 else if (acpi_dock_match(handle))
> >>                         acpi_add_id(pnp, ACPI_DOCK_HID);
> >> diff --git a/include/acpi/acpi_bus.h b/include/acpi/acpi_bus.h
> >> index cd3b75e08ec3..e44be31115a6 100644
> >> --- a/include/acpi/acpi_bus.h
> >> +++ b/include/acpi/acpi_bus.h
> >> @@ -230,7 +230,8 @@ struct acpi_pnp_type {
> >>         u32 hardware_id:1;
> >>         u32 bus_address:1;
> >>         u32 platform_id:1;
> >> -       u32 reserved:29;
> >> +       u32 backlight:1;
> >> +       u32 reserved:28;
> >>  };
> >>
> >>  struct acpi_device_pnp {
> >> --
> >
> > Applied as 6.2-rc material, thanks!
>
> Thanks.
>
> I just realized this probably needs a:
>
> Fixes: 63f534b8bad9 ("ACPI: PCI: Rework acpi_get_pci_dev()")
>
> tag, so that it gets picked up for 6.1.y

I've added that tag to it, thanks!