Re: [PATCH i-g-t 1/7] lib/igt_device_scan: Don't print fake link bandwidth attributes

[Sebastian Brzezinka <sebastian.brzezinka@intel.com>]

On Wed Jan 21, 2026 at 12:42 PM CET, Janusz Krzysztofik wrote:
> Users of Intel discrete graphics adapters are confused with fake
> information on PCIe link bandwidth (speed and size) of their GPU devices
> reported by tools like lspci or lsgpu.  That fake information is
> unfortunately provided by hardware, Linux PCI subsystem just exposes it
> untouched to upper layers, including userspace via sysfs, and userspace
> tools just report those fake values.
>
> While we can't do much about the kernel side or general purpose userspace
> tools like lspci, we can try to address the issue with our lsgpu utility.
>
> Correct link bandwidth attributes of a discrete GPU card can be obtained
> from the kernel by looking not at the PCI device of the GPU itself, only
> at a PCIe upstream port of the card's PCI bridge.  For integrity with
> content of the sysfs and with output from the other tools, we are not
> going to replace the fake information with that from the bridge upstream
> port, only show that port and its attributes themselves while listing
> devices.
>
> Since the tool uses our udev based igt_device_scan library for identifying
> GPU devices and printing their properties and attributes, modifications
> that we need apply to that library.
>
> As a first step, exclude the fake data from being printed.
>
> Link: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/10753
> Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@linux.intel.com>
> ---
>  lib/igt_device_scan.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/lib/igt_device_scan.c b/lib/igt_device_scan.c
> index abd8ca209e..7753262a53 100644
> --- a/lib/igt_device_scan.c
> +++ b/lib/igt_device_scan.c
> @@ -613,6 +613,14 @@ static void dump_props_and_attrs(const struct igt_device *dev)
>  
>  	printf("\n[attributes]\n");
>  	igt_map_foreach(dev->attrs_map, entry) {
> +		/* omit fake link bandwidth attributes */
> +		if (dev->dev_type == DEVTYPE_DISCRETE &&
> +		    (!strcmp(entry->key, "max_link_speed") ||
> +		     !strcmp(entry->key, "max_link_width") ||
> +		     !strcmp(entry->key, "current_link_speed") ||
> +		     !strcmp(entry->key, "current_link_width")))
> +			continue;
> +
Nit: This might be a bit confusing now that the return value depends on DEVTYPE_DISCRETE,
especially for a library. I know it’s extra work to keep it generic, but maybe we could
move the check to its own function just to clean things up a bit?

-- 
Best regards,
Sebastian