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

["Laguna, Lukasz" <lukasz.laguna@intel.com>]

On 9/16/2026 13:51, Piórkowski, Piotr wrote:
> 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)

I don't see it's ever used in this series.

> +{
> +	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);