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;
--
2.39.0
