On Monday, January 9, 2023 9:57:21 PM CET 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.
Interesting. Sorry for the trouble.
> 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.
This has a potential of changing the behavior in some cases that are not
relevant here which is generally risky.
> 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.
I agree with the above, but my fix would be something like the patch below (not
really tested, but it builds).
---
drivers/acpi/glue.c | 14 ++++++++++++--
drivers/acpi/scan.c | 7 +++++--
include/acpi/acpi_bus.h | 3 ++-
3 files changed, 19 insertions(+), 5 deletions(-)
Index: linux-pm/include/acpi/acpi_bus.h
===================================================================
--- linux-pm.orig/include/acpi/acpi_bus.h
+++ linux-pm/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 {
Index: linux-pm/drivers/acpi/scan.c
===================================================================
--- linux-pm.orig/drivers/acpi/scan.c
+++ linux-pm/drivers/acpi/scan.c
@@ -1370,9 +1370,12 @@ static void acpi_set_pnp_ids(acpi_handle
* 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);
Index: linux-pm/drivers/acpi/glue.c
===================================================================
--- linux-pm.orig/drivers/acpi/glue.c
+++ linux-pm/drivers/acpi/glue.c
@@ -75,7 +75,8 @@ static struct acpi_bus_type *acpi_get_bu
}
#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
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;
