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

[Rafael J. Wysocki]

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!