This is a note to let you know that I've just added the patch titled ACPI / scan: Prefer devices without _HID/_CID for _ADR matching to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: acpi-scan-prefer-devices-without-_hid-_cid-for-_adr-matching.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From foo@baz Fri Aug 4 15:15:51 PDT 2017 From: "Rafael J. Wysocki" <rafael.j.wysocki@xxxxxxxxx> Date: Fri, 30 Dec 2016 02:27:31 +0100 Subject: ACPI / scan: Prefer devices without _HID/_CID for _ADR matching From: "Rafael J. Wysocki" <rafael.j.wysocki@xxxxxxxxx> [ Upstream commit c2a6bbaf0c5f90463a7011a295bbdb7e33c80b51 ] The way acpi_find_child_device() works currently is that, if there are two (or more) devices with the same _ADR value in the same namespace scope (which is not specifically allowed by the spec and the OS behavior in that case is not defined), the first one of them found to be present (with the help of _STA) will be returned. This covers the majority of cases, but is not sufficient if some of the devices in question have a _HID (or _CID) returning some valid ACPI/PNP device IDs (which is disallowed by the spec) and the ASL writers' expectation appears to be that the OS will match devices without a valid ACPI/PNP device ID against a given bus address first. To cover this special case as well, modify find_child_checks() to prefer devices without ACPI/PNP device IDs over devices that have them. Suggested-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> Tested-by: Hans de Goede <hdegoede@xxxxxxxxxx> Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/acpi/glue.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) --- a/drivers/acpi/glue.c +++ b/drivers/acpi/glue.c @@ -98,7 +98,15 @@ static int find_child_checks(struct acpi if (check_children && list_empty(&adev->children)) return -ENODEV; - return sta_present ? FIND_CHILD_MAX_SCORE : FIND_CHILD_MIN_SCORE; + /* + * If the device has a _HID (or _CID) returning a valid ACPI/PNP + * device ID, it is better to make it look less attractive here, so that + * the other device with the same _ADR value (that may not have a valid + * device ID) can be matched going forward. [This means a second spec + * violation in a row, so whatever we do here is best effort anyway.] + */ + return sta_present && list_empty(&adev->pnp.ids) ? + FIND_CHILD_MAX_SCORE : FIND_CHILD_MIN_SCORE; } struct acpi_device *acpi_find_child_device(struct acpi_device *parent, Patches currently in stable-queue which might be from rafael.j.wysocki@xxxxxxxxx are queue-4.4/pm-domains-defer-dev_pm_domain_set-until-genpd-attach_dev-succeeds-if-present.patch queue-4.4/acpi-scan-prefer-devices-without-_hid-_cid-for-_adr-matching.patch