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b=nQ1C5Iqig91cHmIsHztCCidLQcIVmFSDzD0s3+rBxkGZlfb9r/wPKoqH2Kclwx/RYAAst62rPKkoGvh03OpZOyiIGTFGKgUqTy5Xz5oKZ8mPedKtjpVgOtutPpDO8JUvtR1GN7Lunepl2blyt8/q2LI6tGuHofE8QhIMb5Wks1g= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from DS7PR12MB5766.namprd12.prod.outlook.com (2603:10b6:8:75::12) by DS4PR12MB9771.namprd12.prod.outlook.com (2603:10b6:8:29b::10) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.71.12; Fri, 29 May 2026 04:30:25 +0000 Received: from DS7PR12MB5766.namprd12.prod.outlook.com ([fe80::222:966a:d65d:d08e]) by DS7PR12MB5766.namprd12.prod.outlook.com ([fe80::222:966a:d65d:d08e%3]) with mapi id 15.21.0071.010; Fri, 29 May 2026 04:30:25 +0000 Message-ID: <4a270b89-6512-4332-8f27-10b7daa90daa@amd.com> Date: Fri, 29 May 2026 10:00:21 +0530 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 3/3] iommu/amd: Dynamically verify Southbridge IOAPIC via PCI config space To: Wei Wang , joro@8bytes.org, suravee.suthikulpanit@amd.com, will@kernel.org, robin.murphy@arm.com, thomas.lendacky@amd.com, aik@amd.com, jgg@nvidia.com, kevin.tian@intel.com, xuyongwei@open-hieco.net Cc: iommu@lists.linux.dev, linux-kernel@vger.kernel.org References: Content-Language: en-US From: Vasant Hegde In-Reply-To: Content-Type: text/plain; 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Currently, > if the SB IOAPIC entry in the IVRS table does not match a historically > hardcoded device ID (00:14.0), interrupt remapping is forcibly disabled. > > This hardcoded expectation does not scale to newer architectures. For > example, recent Hygon Gen 4 servers use 00:0b.0 for the SB IOAPIC, > causing the validation to fail and interrupt remapping to be permanently > disabled on these systems. > > Because the SB IOAPIC is embedded within the FCH (Fusion Controller Hub) > and shares its device ID, we can inspect the PCI class code of the given > device ID to confirm it is an actual FCH device, which is typically > exposed as an SMBus controller function. The PCI class code at a given BDF > is a stable, specification-defined property. Using it to identify an FCH > function avoids maintaining per-vendor/per-generation hardcoded device IDs > that must be updated for new platforms, while producing the same safe > fallback (IR disabled) if the check ever fails. > > Signed-off-by: Wei Wang Reviewed-by: Vasant Hegde -Vasant