[PATCH i-g-t 4/4] lib/igt_device_scan: Fix scan vs bind/unbind/reload

[Zbigniew Kempczyński]

On Tue, Dec 17, 2024 at 09:13:24PM -0800, Lucas De Marchi wrote:
> There's no guarantee a card will end up with the same device node when
> modules are loaded/unloaded and drivers bound/unbound. There's some
> fundamental issue with the igt's the way it is and it's also puzzling
> from the logs it looks like the device vanished from the bus, when in
> reality is just the SW state out of sync with what the kernel is
> exporting.
> 
> Re-scanning when trying to match a device is not expensive compared to
> what most tests are doing, so simply force it to occur whenever trying
> to match a card.

I also should comment the above. It is generally true, but I've noticed
getting attributes might be expensive. Even it may take up to few
seconds, that's why I've added some attributes we don't fetch from udev
(see is_on_blacklist()). If I'm not wrong getting 'config' was a cause
to limit attributes we fetch.

--
Zbigniew

> 
> Example for xe_wedged:
> 
> 	$ sudo ./build/tests/xe_wedged --device pci:0000:03:00.0 --r wedged-at-any-timeout
> 	(xe_wedged:11173) drmtest-DEBUG: Looking for devices to open using filter 0: pci:0000:03:00.0
> 	(xe_wedged:11173) drmtest-DEBUG: Filter matched /dev/dri/card1 | /dev/dri/renderD129
> 
> 	... [ wedge and rebind here ]
> 
> 	(xe_wedged:11173) drmtest-DEBUG: Looking for devices to open using filter 0: pci:0000:03:00.0
> 	(xe_wedged:11173) drmtest-DEBUG: Filter matched /dev/dri/card2 | /dev/dri/renderD130
> 
> Signed-off-by: Lucas De Marchi <lucas.demarchi at intel.com>
> ---
>  lib/igt_device_scan.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/igt_device_scan.c b/lib/igt_device_scan.c
> index 8e2297087..956719fba 100644
> --- a/lib/igt_device_scan.c
> +++ b/lib/igt_device_scan.c
> @@ -1983,7 +1983,7 @@ static bool __igt_device_card_match(const char *filter,
>  	 * Scan devices in case the user hasn't yet,
>  	 * but leave a decision on forced rescan on the user side.
>  	 */
> -	igt_devices_scan(false);
> +	igt_devices_scan(true);
>  
>  	if (igt_device_filter_apply(filter) == false)
>  		return false;
> -- 
> 2.47.0
>