p.s. This fixes a regression in 6.1, adding the regressions list to the Cc.
Once we figure out the best way to fix this (this patch is more of a proposal how to fix this rather then a definitive fix), we should also backport the fix to 6.1.y. On 1/9/23 21:57, Hans de Goede 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. > > Make find_child_checks() return a higher score for children which have > pnp-ids set by various scan helpers like acpi_is_video_device(), so > that it picks the right companion-device. > > An alternative approach would be to directly call acpi_is_video_device() > from find_child_checks() but that would be somewhat computationally > expensive given that acpi_find_child_device() iterates over all the > PCI0 children every time it is called. > > Fixes: 63f534b8bad9 ("ACPI: PCI: Rework acpi_get_pci_dev()") > Signed-off-by: Hans de Goede <hdego...@redhat.com> > --- > drivers/acpi/glue.c | 14 ++++++++++++-- > 1 file changed, 12 insertions(+), 2 deletions(-) > > diff --git a/drivers/acpi/glue.c b/drivers/acpi/glue.c > index 204fe94c7e45..2055dfd7678b 100644 > --- a/drivers/acpi/glue.c > +++ b/drivers/acpi/glue.c > @@ -75,7 +75,7 @@ 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_MAX_SCORE 3 > > static int match_any(struct acpi_device *adev, void *not_used) > { > @@ -89,15 +89,25 @@ static bool acpi_dev_has_children(struct acpi_device > *adev) > > static int find_child_checks(struct acpi_device *adev, bool check_children) > { > + int score = FIND_CHILD_MIN_SCORE; > unsigned long long sta; > acpi_status status; > > if (check_children && !acpi_dev_has_children(adev)) > return -ENODEV; > > + /* > + * For devices without a _STA method, prefer devices without a _HID > + * (which conflicts with having an _ADR) but which have been matched > + * in some other way, like e.g. by acpi_is_video_device() over devices > + * with no ids at all. > + */ > + if (!adev->pnp.type.platform_id && adev->pnp.type.hardware_id) > + score++; > + > status = acpi_evaluate_integer(adev->handle, "_STA", NULL, &sta); > if (status == AE_NOT_FOUND) > - return FIND_CHILD_MIN_SCORE; > + return score; > > if (ACPI_FAILURE(status) || !(sta & ACPI_STA_DEVICE_ENABLED)) > return -ENODEV;