Re: [PATCH v2] iommu/amd: Allow matching ACPI HID devices without matching UIDs

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

Hi Mario,

On 5/5/2025 8:14 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:
> ```
> [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. Other
> operating systems allow this, but the current IVRS spec doesn't explicitly
> allow or disallow it. Output 'Firmware Bug' for this case to encourage it to
> be solved in the BIOS.
> 
> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
> ---
> v2:
>  * Use FW_BUG
>  * Update commit message
> Cc: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
> Cc: Vasant Hegde <Vasant.Hegde@amd.com>
> Cc: Paul Blinzer <Paul.Blinzer@amd.com>
> ---
>  drivers/iommu/amd/iommu.c | 24 ++++++++++++++++++++----
>  1 file changed, 20 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
> index b19e8c0f48fa2..06f747d2f964c 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;
> +	bool fw_bug;

Initialize these variables?

>  
>  	if (!adev)
>  		return -ENODEV;
> @@ -117,11 +118,26 @@ 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;
> +			fw_bug = false;
> +			break;
> +		}
> +
> +		/* In ase there is no UID match, but exactly one HID match */
> +		if (acpi_dev_hid_match(adev, p->hid)) {
> +			p1 = p;
> +			fw_bug = true;

I am not sure why you dropped counter from v1. I think we still need HID match
counter so that function returns -ENODEV if HID match counter > 1?

-Vasant

>  		}
>  	}
> +
> +	if (p1) {
> +		if (fw_bug)
> +			dev_err_once(dev, FW_BUG "No matching UID in ACPI tables, but found matching HID.\n");
> +		if (entry)
> +			*entry = p1;
> +		return p1->devid;
> +	}
> +
>  	return -EINVAL;
>  }
>