[PATCH] iommu/amd: Allow matching ACPI HID devices without matching UIDs

[Mario Limonciello <superm1@kernel.org>]

From: Mario Limonciello <mario.limonciello@amd.com>

A BIOS upgrade has changed the IVRS DTE UID for a device that no
longer matches the UID in the SSDT.  Checking with BIOS team, this is
intended behavior, however it breaks the existing logic check in
get_acpihid_device_id().

In this case there is only one ACPI device on the system with that _HID
but the _UID mismatch.

IVRS:
```
[1E4h 0484 001h]               Subtable Type : F0 [Device Entry: ACPI HID Named Device]
[1E5h 0485 002h]                   Device ID : 0060
[1E7h 0487 001h] Data Setting (decoded below) : 40
                                    INITPass : 0
                                    EIntPass : 0
                                     NMIPass : 0
                                    Reserved : 0
                                 System MGMT : 0
                                  LINT0 Pass : 1
                                  LINT1 Pass : 0
[1E8h 0488 008h]                    ACPI HID : "MSFT0201"
[1F0h 0496 008h]                    ACPI CID : 0000000000000000
[1F8h 0504 001h]                  UID Format : 02
[1F9h 0505 001h]                  UID Length : 09
[1FAh 0506 009h]                         UID : "\_SB.MHSP"
```

SSDT:
```
Device (MHSP)
{
    Name (_ADR, Zero)  // _ADR: Address
    Name (_HID, "MSFT0201")  // _HID: Hardware ID
    Name (_UID, One)  // _UID: Unique ID
```

To handle this case; while enumerating ACPI devices in get_acpihid_device_id()
count the number of matching ACPI devices with a matching _HID. If there is
exactly one _HID match then accept it even if the UID doesn't match.

Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
---
 drivers/iommu/amd/iommu.c | 24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
index b19e8c0f48fa2..f9fad07edeeb7 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -109,7 +109,8 @@ static inline int get_acpihid_device_id(struct device *dev,
 					struct acpihid_map_entry **entry)
 {
 	struct acpi_device *adev = ACPI_COMPANION(dev);
-	struct acpihid_map_entry *p;
+	struct acpihid_map_entry *p, *p1;
+	int hid_count = 0;
 
 	if (!adev)
 		return -ENODEV;
@@ -117,12 +118,25 @@ static inline int get_acpihid_device_id(struct device *dev,
 	list_for_each_entry(p, &acpihid_map, list) {
 		if (acpi_dev_hid_uid_match(adev, p->hid,
 					   p->uid[0] ? p->uid : NULL)) {
-			if (entry)
-				*entry = p;
-			return p->devid;
+			p1 = p;
+			hid_count = 1;
+			break;
+		}
+
+		/* If there is no UID match, but exactly one HID match, return that match */
+		if (acpi_dev_hid_match(adev, p->hid)) {
+			p1 = p;
+			hid_count++;
 		}
 	}
-	return -EINVAL;
+
+	if (hid_count != 1)
+		return -EINVAL;
+
+	if (entry)
+		*entry = p1;
+
+	return p1->devid;
 }
 
 static inline int get_device_sbdf_id(struct device *dev)
-- 
2.43.0