[PATCH] ACPI: return first _ADR match for acpi_get_child

[Lekensteyn <lekensteyn@gmail.com>]

From: Peter Wu <lekensteyn@gmail.com>

When acpi_get_child is called, it loops through all direct child
devices and calls do_acpi_find_child to find an ACPI handle matching the
_ADR. The previous implementation visits every direct child, if there
were multiple devices with a matching _ADR, the last match was always
returned.

This behaviour (returning the last result) does not work for many recent
Lenovo machines when looking for the correct ACPI handle for a Nvidia
PCI video device. On these machines, the first handle should be used
instead of the last one. On these machines, the PCI Bus ID is 01:00.0,
hence the address that is searched for is 0 (via acpi_pci_find_device).

When acpi_pci_find_device calls acpi_get_child, it iterates through:

    Address: 00000000 (valid); handle: \_SB_.PCI0.PEG0.PEGP
    Address: 00000001 (valid); handle: \_SB_.PCI0.PEG0.VGA1
    Address: 00000000 (valid); handle: \_SB_.PCI0.PEG0.VGA_

The correct handle here is "\_SB_.PCI0.PEG0.PEGP" which contains the
_ROM method as well as _PSx for PM, and not \_SB.PCI0.PEG0.VGA.

On my own laptop, and many others I believe, there is only one matching
handle for a PCI device. The acpi_get_child method has been added in
2005, 4e10d12a3d88c88fba3258809aa42d14fd8cf1d1, and there is no message
indicating that the last (or first) handle should be returned. However,
it is kind of useless to iterate from beginning to the end if you only
need the last match. Therefore, just return the first match (which is
likely the last one too in almost all cases).

Verified to work for an affected Lenovo Ideapad Y480, tested for no
regressions on my laptop (Clevo B7130).

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=42696

Tested-by: Sergio Perez <dagobertstaler@gmail.com>
Signed-off-by: Peter Wu <lekensteyn@gmail.com>
---
 drivers/acpi/glue.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/acpi/glue.c b/drivers/acpi/glue.c
index 0837308..dc9c945 100644
--- a/drivers/acpi/glue.c
+++ b/drivers/acpi/glue.c
@@ -99,18 +99,20 @@ struct acpi_find_child {
 static acpi_status
 do_acpi_find_child(acpi_handle handle, u32 lvl, void *context, void **rv)
 {
-	acpi_status status;
+	acpi_status status, ret = AE_OK;
 	struct acpi_device_info *info;
 	struct acpi_find_child *find = context;
 
 	status = acpi_get_object_info(handle, &info);
 	if (ACPI_SUCCESS(status)) {
 		if ((info->address == find->address)
-			&& (info->valid & ACPI_VALID_ADR))
+			&& (info->valid & ACPI_VALID_ADR)) {
 			find->handle = handle;
+			ret = AE_CTRL_TERMINATE;
+		}
 		kfree(info);
 	}
-	return AE_OK;
+	return ret;
 }
 
 acpi_handle acpi_get_child(acpi_handle parent, u64 address)
-- 
1.8.0