[PATCH v1 1/4] lib/igt_pci: Add raw configuration space helpers

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

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

Add helpers to read raw PCI configuration space from sysfs and access
its contents.
Provide little-endian u16/u32 readers and standard capability lookup
helpers for configuration-space buffers.

Signed-off-by: Piotr Piórkowski <piotr.piorkowski@intel.com>
Assisted-by: GPT-5.6 Luna
---
 lib/igt_pci.c | 86 +++++++++++++++++++++++++++++++++++++++++++++++++++
 lib/igt_pci.h |  7 +++++
 2 files changed, 93 insertions(+)

diff --git a/lib/igt_pci.c b/lib/igt_pci.c
index b63550b390..06717fe8eb 100644
--- a/lib/igt_pci.c
+++ b/lib/igt_pci.c
@@ -61,6 +61,92 @@ 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);
 }
 
+/**
+ * igt_pci_config_raw_read:
+ * @pci_slot: PCI device BDF (e.g. "0000:01:00.0")
+ * @buffer: destination buffer
+ * @length: number of configuration-space bytes to read
+ *
+ * Read raw PCI configuration space through the device sysfs config attribute.
+ *
+ * Returns 0 on success, otherwise a negative errno-like value.
+ */
+int igt_pci_config_raw_read(const char *pci_slot, void *buffer, size_t length)
+{
+	char path[PATH_MAX];
+	ssize_t ret;
+	int err;
+	int fd;
+
+	if (!pci_slot || !buffer || !length)
+		return -EINVAL;
+
+	snprintf(path, sizeof(path), "/sys/bus/pci/devices/%s/config", pci_slot);
+	fd = open(path, O_RDONLY | O_CLOEXEC);
+	if (fd < 0)
+		return -errno;
+
+	ret = pread(fd, buffer, length, 0);
+	err = errno;
+	close(fd);
+	if (ret < 0)
+		return -err;
+
+	return (size_t)ret == length ? 0 : -EIO;
+}
+
+uint16_t igt_pci_config_raw_read_u16(const uint8_t *config, unsigned int offset)
+{
+	return config[offset] | (config[offset + 1] << 8);
+}
+
+uint32_t igt_pci_config_raw_read_u32(const uint8_t *config, unsigned int offset)
+{
+	return igt_pci_config_raw_read_u16(config, offset) |
+	       ((uint32_t)igt_pci_config_raw_read_u16(config, offset + 2) << 16);
+}
+
+int igt_pci_config_raw_find_cap_offset(const uint8_t *config, uint8_t cap_id)
+{
+	unsigned int offset = config[PCI_CAPS_START];
+	unsigned int loop = (PCI_CFG_SPACE_SIZE - PCI_TYPE0_1_HEADER_SIZE) / 2;
+
+	while (offset && loop--) {
+		if (offset < PCI_TYPE0_1_HEADER_SIZE || offset >= PCI_CFG_SPACE_SIZE)
+			return -EINVAL;
+
+		if (config[offset] == cap_id)
+			return offset;
+
+		offset = config[offset + 1];
+	}
+
+	return offset ? -ELOOP : 0;
+}
+
+int igt_pci_config_raw_find_ext_cap_offset(const uint8_t *config, uint16_t cap_id)
+{
+	unsigned int offset = PCI_EXT_CAPS_START;
+	unsigned int loop = (PCI_EXT_CFG_SPACE_SIZE - offset) / 4;
+
+	while (loop--) {
+		uint32_t header = igt_pci_config_raw_read_u32(config, offset);
+
+		if (!header)
+			break;
+		if ((header & 0xffff) == cap_id)
+			return offset;
+
+		offset = (header >> 20) & 0xffc;
+		if (!offset)
+			break;
+		if (offset < PCI_EXT_CAPS_START || offset >= PCI_EXT_CFG_SPACE_SIZE)
+			return -EINVAL;
+	}
+
+	return loop ? 0 : -ELOOP;
+}
+
 static int open_pci_driver_dir(const char *driver)
 {
 	char path[PATH_MAX];
diff --git a/lib/igt_pci.h b/lib/igt_pci.h
index 509345b2d8..787c10fc51 100644
--- a/lib/igt_pci.h
+++ b/lib/igt_pci.h
@@ -16,6 +16,8 @@ struct pci_device;
 #define PCI_TYPE0_1_HEADER_SIZE 0x40
 #define PCI_CAPS_START 0x34
 #define PCI_CFG_SPACE_SIZE 0x100
+#define PCI_EXT_CAPS_START 0x100
+#define PCI_EXT_CFG_SPACE_SIZE 0x1000
 
 enum pci_cap_id {
 	PCI_EXPRESS_CAP_ID = 0x10
@@ -27,6 +29,11 @@ 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 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);
+int igt_pci_config_raw_find_cap_offset(const uint8_t *config, uint8_t cap_id);
+int igt_pci_config_raw_find_ext_cap_offset(const uint8_t *config, uint16_t cap_id);
 int igt_pci_device_unbind(const char *pci_slot);
 int igt_pci_driver_bind(const char *driver, const char *pci_slot);
 int igt_pci_driver_unbind(const char *driver, const char *pci_slot);
-- 
2.34.1