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 <hdegoede@xxxxxxxxxx>
> ---
> 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;
