Re: [PATCH v3] iommu/amd: Allow matching ACPI HID devices without matching UIDs

[Vasant Hegde <vasant.hegde@amd.com>]

On 5/12/2025 11:00 PM, Mario Limonciello wrote:
> 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. In this case there is only
> one ACPI device on the system with that _HID but the _UID mismatch.
> 
> IVRS:
> ```
>               Subtable Type : F0 [Device Entry: ACPI HID Named Device]
>                   Device ID : 0060
> Data Setting (decoded below) : 40
>                  INITPass : 0
>                  EIntPass : 0
>                  NMIPass : 0
>                  Reserved : 0
>                  System MGMT : 0
>                  LINT0 Pass : 1
>                  LINT1 Pass : 0
>                    ACPI HID : "MSFT0201"
>                    ACPI CID : 0000000000000000
>                  UID Format : 02
>                  UID Length : 09
>                         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. Other operating systems allow this, but the
> current IVRS spec leaves some ambiguity whether to allow or disallow it.
> This should be clarified in future revisions of the spec. Output
> 'Firmware Bug' for this case to encourage it to be solved in the BIOS.
> 
> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
> ---
> v3:
>  * Count HID matches as well (cover # HID w/o UID > 2)
>  * Drop level of indentation with early bail on error
>  * Show number of matches in error message
>  * Adjust commit message
> Cc: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
> Cc: Vasant Hegde <Vasant.Hegde@amd.com>
> Cc: Paul Blinzer <Paul.Blinzer@amd.com>

Reviewed-by: Vasant Hegde <vasant.hegde@amd.com>

-Vasant