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

[Lucas De Marchi]

On Wed, Dec 18, 2024 at 07:34:19AM +0100, Zbigniew Kempczyński wrote:
>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.

why would we get all attributes and exclude some?  Shouldn't we get only
the attributes we actually use? AFAIK this logic is basically used by
--device/IGT_DEVICE, right? What filters we normally use?

I usually pass the pci slot (because I know that won't change
dynamically and cause surprises). Apparently CI passes vendor/devid:

	export IGT_DEVICE=pci:vendor=$1,device=$2

(but it seems to vary depending on pipeline)

Some devs pass the device node directly too as in a lot of places
there's only ever card0 possible.

Are there other uses?

thanks
Lucas De Marchi

>
>--
>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
>>