Hi Rafael,
On 1/10/23 14:33, Rafael J. Wysocki wrote:
> 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.
No problem, as mentioned this is actually a long standing issue / bug
in the ACPI tables, it just never surfaced before.
>> 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).
Thanks, I have just given this a spin on my E6430 and I can confirm
it still fixes things.
I'll send out this version (re-using most of the v1 commitmsg) as a v2
right away.
Regards,
Hans
>
> ---
> 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;
>
>
>
