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b=a2178IyASqaevYveHjMGh5RDsofiF1TY5GGVAfAf4+BU0ezrSn3G+hgyo7x+D3OAV4/8lMJIZ1pwTbKNSF8v358LFv2qpNNda302/MwHxfyZOrFeYtYbdU1hN36cnpg2BpGvreKKyr9EkBvQ6fiXhct79zOPtT2pk6AIKfxeukc= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from CH3PR12MB7571.namprd12.prod.outlook.com (2603:10b6:610:147::9) by LVUPR12MB999185.namprd12.prod.outlook.com (2603:10b6:408:3a3::20) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.406.9; Fri, 11 Sep 2026 14:09:14 +0000 Received: from CH3PR12MB7571.namprd12.prod.outlook.com ([fe80::7a06:d977:dd3:6176]) by CH3PR12MB7571.namprd12.prod.outlook.com ([fe80::7a06:d977:dd3:6176%5]) with mapi id 15.21.0406.007; Fri, 11 Sep 2026 14:09:11 +0000 Message-ID: <58e8a8f9-6e5e-4c29-a974-7b3d6413ab48@amd.com> Date: Fri, 11 Sep 2026 16:09:06 +0200 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] PCI: Accept AtomicOps already enabled by the hypervisor To: =?UTF-8?Q?Christian_K=C3=B6nig?= , Nikola Prica , bhelgaas@google.com Cc: linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, jerry.jiang@amd.com, haijun.chang@amd.com, andy.zhang@amd.com, jim.chow@broadcom.com, matthew.mcclure@broadcom.com, "Deucher, Alexander" References: <20260903121217.23F751F000E9@smtp.kernel.org> <20260907161701.454364-1-nikprica@amd.com> <9a71c692-66e7-4c5a-b98a-69ebae2e5bb8@amd.com> Content-Language: en-US From: "Prica, Nikola" In-Reply-To: <9a71c692-66e7-4c5a-b98a-69ebae2e5bb8@amd.com> Content-Type: text/plain; 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Do you need more information? Thanks, Nikola On 9/8/2026 10:47 AM, Christian König wrote: > On 9/7/26 18:17, Nikola Prica wrote: >> From: Nikola Prica >> >> pci_enable_atomic_ops_to_root() currently fails when no root port is >> visible. That is common in passthrough guests (ESXi, Hyper-V): the >> endpoint is assigned to the VM, but the guest topology has no root >> port above it. >> >> In those setups the hypervisor may already have enabled AtomicOp >> requester enable on the device. If PCI_EXP_DEVCTL2_ATOMIC_REQ is set, >> treat AtomicOps as already enabled and return success instead of >> failing the Root Port walk. >> >> Signed-off-by: Nikola Prica > > Reviewed-by: Christian König > > Bjorn first of all any objections to this? It sounds save to me, only a handful of drivers actually use this function and it generally seems to be the right things to do. > > Then if you agree any objections to up-streaming it through AMDs GPU branch? That would make things a bit easier for us. > > Thanks, > Christian. > >> --- >> Changes in v2: >> - Be more strict and only apply logic in headless device case. >> >> drivers/pci/pci.c | 12 +++++++++++- >> 1 file changed, 11 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c >> index b2879a6be5f8..62729ade496f 100644 >> --- a/drivers/pci/pci.c >> +++ b/drivers/pci/pci.c >> @@ -3769,8 +3769,18 @@ int pci_enable_atomic_ops_to_root(struct pci_dev *dev, u32 cap_mask) >> } >> >> root = pcie_find_root_port(dev); >> - if (!root) >> + if (!root) { >> + /* >> + * A hypervisor may expose a headless topology with no >> + * visible root port. If it has already set AtomicOp >> + * Requester Enable, there is nothing more to do. >> + */ >> + pcie_capability_read_dword(dev, PCI_EXP_DEVCTL2, &ctl2); >> + if (ctl2 & PCI_EXP_DEVCTL2_ATOMIC_REQ) >> + return 0; >> + >> return -EINVAL; >> + } >> >> pcie_capability_read_dword(root, PCI_EXP_DEVCAP2, &cap); >> if ((cap & cap_mask) != cap_mask) >