[PATCH for v4.9 LTS 32/87] ACPI / scan: Prefer devices without _HID/_CID for _ADR matching

From: Levin, Alexander (Sasha Levin)
Date: Fri Jul 14 2017 - 21:39:37 EST

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>
drivers/acpi/glue.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/acpi/glue.c b/drivers/acpi/glue.c
index 5ea5dc219f56..73c9c7fa9001 100644
--- a/drivers/acpi/glue.c
+++ b/drivers/acpi/glue.c
@@ -98,7 +98,15 @@ static int find_child_checks(struct acpi_device *adev, bool check_children)
if (check_children && list_empty(&adev->children))
return -ENODEV;

+ /*
+ * 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) ?

struct acpi_device *acpi_find_child_device(struct acpi_device *parent,