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Wed, 30 Sep 2026 10:09:09 -0400 X-MC-Unique: SOCXgrpmO5qWs48VnazhLw-1 X-Mimecast-MFC-AGG-ID: SOCXgrpmO5qWs48VnazhLw_1790777347 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 098451954B1D; Wed, 30 Sep 2026 14:09:07 +0000 (UTC) Received: from jtornosm-thinkpadp1gen7.rmtes.csb (headnet04.pony-001.prod.iad2.dc.redhat.com [10.2.32.116]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 717C31956044; Wed, 30 Sep 2026 14:09:02 +0000 (UTC) From: Jose Ignacio Tornos Martinez To: bhelgaas@google.com, alex@shazbot.org, jjohnson@kernel.org Cc: johannes@sipsolutions.net, mani@kernel.org, jgg@ziepe.ca, yishaih@nvidia.com, skolothumtho@nvidia.com, kevin.tian@intel.com, linux-pci@vger.kernel.org, kvm@vger.kernel.org, linux-wireless@vger.kernel.org, ath11k@lists.infradead.org, ath12k@lists.infradead.org, linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org, Jose Ignacio Tornos Martinez Subject: [PATCH 1/7] PCI: Add pci_find_free_ext_cap_offset() helper Date: Wed, 30 Sep 2026 16:08:27 +0200 Message-ID: <20260930140833.576941-2-jtornosm@redhat.com> In-Reply-To: <20260930140833.576941-1-jtornosm@redhat.com> References: <20260930140833.576941-1-jtornosm@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 X-Mimecast-MFC-PROC-ID: TEjYnhjHwdClX7W-2PYuFKMkGLMah6uDvBDRDldN-kU_1790777347 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit content-type: text/plain; charset="US-ASCII"; x-default=true X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260930_151104_794335_6912AA47 X-CRM114-Status: GOOD ( 18.86 ) X-BeenThere: ath11k@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "ath11k" Errors-To: ath11k-bounces+ath11k=archiver.kernel.org@lists.infradead.org Add helper function to find free space in PCI extended configuration space. This is needed by VFIO variant drivers that need to use unused extended config space for device-specific purposes, such as passing metadata to VMs. The function scans the extended capability chain and returns an offset to a gap of at least the requested size. This allows drivers to safely use extended config space without conflicting with existing capabilities. Use case: The qcom-vfio-pci variant driver uses this to find space for caching host MSI addresses that need to be passed to Qualcomm device firmware in VMs. Signed-off-by: Jose Ignacio Tornos Martinez --- drivers/pci/pci.c | 54 +++++++++++++++++++++++++++++++++++++++++++++ include/linux/pci.h | 3 +++ 2 files changed, 57 insertions(+) diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c index 8f7cfcc00090..7fa261140457 100644 --- a/drivers/pci/pci.c +++ b/drivers/pci/pci.c @@ -552,6 +552,60 @@ u16 pci_find_ext_capability(struct pci_dev *dev, int cap) } EXPORT_SYMBOL_GPL(pci_find_ext_capability); +/** + * pci_find_free_ext_cap_offset - Find free space in extended config + * @dev: PCI device to query + * @size: Minimum size needed (in bytes) + * + * Scans the extended capability chain to find a gap of at least @size bytes + * in the extended configuration space (0x100-0xFFF). This can be used by + * drivers that need to use unused extended config space for device-specific + * purposes (e.g., VFIO quirks for VM passthrough). + * + * Returns the offset to free space, or 0 if no suitable gap found. + */ +int pci_find_free_ext_cap_offset(struct pci_dev *dev, size_t size) +{ + int pos = PCI_CFG_SPACE_SIZE; + int last_cap_start = 0; + int free_offset; + u32 header; + int next; + + if (!pci_is_pcie(dev)) + return 0; + + while (pos >= PCI_CFG_SPACE_SIZE) { + if (pci_read_config_dword(dev, pos, &header)) + break; + + if (header == 0 || header == 0xffffffff) + break; + + last_cap_start = pos; + next = PCI_EXT_CAP_NEXT(header); + if (!next) + break; + pos = next; + } + + /* + * Use space after the last capability. We align to the next capability + * boundary (typically 4-byte aligned). Start at a safe offset past the + * last capability - capabilities vary in size, so use a conservative + * offset. Most extended capabilities are <= 64 bytes. + */ + if (last_cap_start) { + free_offset = last_cap_start + 64; + free_offset = ALIGN(free_offset, 4); + if (PCI_CFG_SPACE_EXP_SIZE - free_offset >= size) + return free_offset; + } + + return 0; +} +EXPORT_SYMBOL_GPL(pci_find_free_ext_cap_offset); + /** * pci_get_dsn - Read and return the 8-byte Device Serial Number * @dev: PCI device to query diff --git a/include/linux/pci.h b/include/linux/pci.h index 2c4454583c11..5d1ccbb2ed29 100644 --- a/include/linux/pci.h +++ b/include/linux/pci.h @@ -1287,6 +1287,7 @@ u8 pci_find_ht_capability(struct pci_dev *dev, int ht_cap); u8 pci_find_next_ht_capability(struct pci_dev *dev, u8 pos, int ht_cap); u16 pci_find_ext_capability(struct pci_dev *dev, int cap); u16 pci_find_next_ext_capability(struct pci_dev *dev, u16 pos, int cap); +int pci_find_free_ext_cap_offset(struct pci_dev *dev, size_t size); struct pci_bus *pci_find_next_bus(const struct pci_bus *from); u16 pci_find_vsec_capability(struct pci_dev *dev, u16 vendor, int cap); u16 pci_find_dvsec_capability(struct pci_dev *dev, u16 vendor, u16 dvsec); @@ -2160,6 +2161,8 @@ static inline u8 pci_find_next_capability(struct pci_dev *dev, u8 post, int cap) { return 0; } static inline u16 pci_find_ext_capability(struct pci_dev *dev, int cap) { return 0; } +static inline int pci_find_free_ext_cap_offset(struct pci_dev *dev, size_t size) +{ return 0; } static inline u64 pci_get_dsn(struct pci_dev *dev) { return 0; } -- 2.53.0