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Fri, 20 Jun 2025 18:56:01 -0700 (PDT) Received: from localhost ([95.85.21.12]) by smtp.gmail.com with UTF8SMTPSA id 4fb4d7f45d1cf-60a18c94acesm2252267a12.44.2025.06.20.18.56.00 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 20 Jun 2025 18:56:01 -0700 (PDT) Date: Sat, 21 Jun 2025 04:55:52 +0300 From: Ahmed Salem To: airlied@redhat.com Cc: lukas@wunner.de, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-kernel-mentees@lists.linux.dev Subject: [RFC PATCH] amd64-agp: do not bind to pci driver if probing fails Message-ID: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Commit 3be5fa236649 ("Revert "iommu/amd: Prevent binding other PCI drivers to IOMMU PCI devices"") had an unintended side effect in that when looking for any AGP bridge, driver_attach() will try to bind to IOMMU devices without preemptively checking for PCI_CAP_ID_AGP capability. This happens during agp_amd64_init(). As a result, driver_attach() calls driver_probe_device(), which then calls really_probe(), raising this critical condition: pci 0000:00:00.2: Resources present before probing With the device being: 00:00.2 IOMMU: Advanced Micro Devices, Inc. [AMD] Raven/Raven2 IOMMU Subsystem: Advanced Micro Devices, Inc. [AMD] Raven/Raven2 IOMMU Flags: bus master, fast devsel, latency 0, IRQ 25 Capabilities: [40] Secure device Capabilities: [64] MSI: Enable+ Count=3D1/4 Maskable- 64bit+ Capabilities: [74] HyperTransport: MSI Mapping Enable+ Fixed+ As pci_register_driver() calls the device's probing function, the latter (agp_amd64_probe) tries to find the device's PCI_CAP_ID_AGP capability, and returns -ENODEV if said capability is not found. Do not attempt driver_attach() if agp_amd64_pci_driver.probe is non-zero to avoid probing already present resources. Link: https://lore.kernel.org/all/aFJOLZ88KIH5WBy2@wunner.de Signed-off-by: Ahmed Salem --- I'm not quite sure whether I should have maintained the linked conversation's Ccs, so please let me know if I should Cc anyone else. Lukas, kindly let me know whether you want me to add a Suggested-by trailer as well. diff --git a/drivers/char/agp/amd64-agp.c b/drivers/char/agp/amd64-agp.c index bf490967241a..e6a0d09e115a 100644 --- a/drivers/char/agp/amd64-agp.c +++ b/drivers/char/agp/amd64-agp.c @@ -768,10 +768,15 @@ int __init agp_amd64_init(void) =20 /* Look for any AGP bridge */ agp_amd64_pci_driver.id_table =3D agp_amd64_pci_promisc_table; - err =3D driver_attach(&agp_amd64_pci_driver.driver); - if (err =3D=3D 0 && agp_bridges_found =3D=3D 0) { + if ((int *)agp_amd64_pci_driver.probe !=3D 0) { pci_unregister_driver(&agp_amd64_pci_driver); err =3D -ENODEV; + } else { + err =3D driver_attach(&agp_amd64_pci_driver.driver); + if (err =3D=3D 0 && agp_bridges_found =3D=3D 0) { + pci_unregister_driver(&agp_amd64_pci_driver); + err =3D -ENODEV; + } } } return err; base-commit: 11313e2f78128c948e9b4eb58b3dacfc30964700 --=20 2.47.2