[PATCH v1 2/4] lib/igt_pci: Add PCI extended capability lookup

["Piórkowski, Piotr" <piotr.piorkowski@intel.com>]

From: Piotr Piórkowski <piotr.piorkowski@intel.com>

Add support for locating PCI Express extended capabilities in raw
configuration space.
Validate the extended capability list while traversing it and report
malformed chains or invalid offsets.

Signed-off-by: Piotr Piórkowski <piotr.piorkowski@intel.com>
Assisted-by: GPT-5.6 Luna
---
 lib/igt_pci.c | 40 ++++++++++++++++++++++++++++++++++++++++
 lib/igt_pci.h |  1 +
 2 files changed, 41 insertions(+)

diff --git a/lib/igt_pci.c b/lib/igt_pci.c
index 06717fe8eb..a87e45c184 100644
--- a/lib/igt_pci.c
+++ b/lib/igt_pci.c
@@ -61,6 +61,46 @@ int find_pci_cap_offset(struct pci_device *dev, enum pci_cap_id cap_id)
 	return find_pci_cap_offset_at(dev, cap_id, PCI_CAPS_START);
 }
 
+/**
+ * find_pci_ext_cap_offset:
+ * @dev: pci device
+ * @cap_id: searched extended capability id, 0 means any capability
+ *
+ * return:
+ * -1 on config read error, 0 if capability is not found,
+ * otherwise offset at which capability with cap_id is found
+ */
+int find_pci_ext_cap_offset(struct pci_device *dev, uint16_t cap_id)
+{
+	uint32_t cap_header;
+	unsigned int offset = PCI_EXT_CAPS_START;
+	int loop = (PCI_EXT_CFG_SPACE_SIZE - PCI_EXT_CAPS_START) / sizeof(cap_header);
+
+	while (loop--) {
+		if (pci_device_cfg_read_u32(dev, &cap_header, offset))
+			return -1;
+
+		if (!cap_header)
+			break;
+
+		if (!cap_id || cap_id == (cap_header & 0xffff))
+			return offset;
+
+		offset = (cap_header >> 20) & 0xffc;
+		if (!offset)
+			break;
+
+		igt_fail_on_f(offset < PCI_EXT_CAPS_START ||
+			      offset >= PCI_EXT_CFG_SPACE_SIZE,
+			      "pci extended capability offset is invalid: 0x%x\n", offset);
+	}
+
+	igt_fail_on_f(loop <= 0 && offset,
+		      "pci extended capability offset doesn't terminate\n");
+
+	return 0;
+}
+
 /**
  * igt_pci_config_raw_read:
  * @pci_slot: PCI device BDF (e.g. "0000:01:00.0")
diff --git a/lib/igt_pci.h b/lib/igt_pci.h
index 787c10fc51..d7d2254678 100644
--- a/lib/igt_pci.h
+++ b/lib/igt_pci.h
@@ -29,6 +29,7 @@ enum pci_cap_id {
 #define  PCI_SLOT_PWR_CTRL_PRESENT (1 << 1)
 
 int find_pci_cap_offset(struct pci_device *dev, enum pci_cap_id cap_id);
+int find_pci_ext_cap_offset(struct pci_device *dev, uint16_t cap_id);
 int igt_pci_config_raw_read(const char *pci_slot, void *buffer, size_t length);
 uint16_t igt_pci_config_raw_read_u16(const uint8_t *config, unsigned int offset);
 uint32_t igt_pci_config_raw_read_u32(const uint8_t *config, unsigned int offset);
-- 
2.34.1