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

[Hans de Goede]

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

Regards,

Hans