[igt-dev] [RFC i-g-t 3/5] lib/igt_device_scan: Remember PCI card index after scanning

[Zbigniew Kempczyński]

On Mon, Nov 16, 2020 at 03:09:43PM +0000, Tvrtko Ursulin wrote:

<cut>
 
> > > +
> > >   /* Core scanning function.
> > >    *
> > >    * All scanned devices are kept inside igt_devs.all pointer array.
> > > @@ -657,6 +685,7 @@ static void scan_drm_devices(void)
> > >   	udev_unref(udev);
> > >   	sort_all_devices();
> > > +	index_pci_devices();
> > >   	igt_list_for_each_entry(dev, &igt_devs.all, link) {
> > >   		struct igt_device *dev_dup = duplicate_device(dev);
> > > @@ -1105,13 +1134,13 @@ static struct igt_list_head *filter_pci(const struct filter_class *fcls,
> > >   		if (filter->data.device && strcasecmp(filter->data.device, dev->device))
> > >   			continue;
> > > -		/* We get n-th card */
> > > -		if (!card) {
> > > -			struct igt_device *dup = duplicate_device(dev);
> > > -			igt_list_add_tail(&dup->link, &igt_devs.filtered);
> > > -			break;
> > > -		}
> > > -		card--;
> > > +		/* Skip if 'card' doesn't match */
> > > +		if (card != dev->pci_index)
> > > +			continue;
> > > +
> > > +		dev = duplicate_device(dev);
> > > +		igt_list_add_tail(&dev->link, &igt_devs.filtered);
> > > +		break;
> > 
> > I may wrong (I got no such testing env) but devs_compare() function along with
> > index_pci_devices() can lead us to such (example) situation:
> > 
> > igt_devs.all contains devices with syspaths and subsystem pci:
> > /sys/devices/pci0000:00/0000:00:04.0	-> vendor 8086, device 1234	pci_index == 0
> > /sys/devices/pci0000:00/0000:00:05.0	-> vendor 8086, device 4321	pci_index == 1
> > /sys/devices/pci0000:00/0000:00:06.0	-> vendor 8086, device 1234	pci_index == 2
> > 
> > If would try filter: pci=vendor=8086,device=1234,card=1 I would expect
> > to select (second card [index == 1]) from filtered devices which match
> > device 1234.
> 
> It is supposed to be like you say, each pci_index being in the namespace of
> equal vendor & device only.
> 
> Like from a dual GPU system:
> 
> $ tools/lsgpu --pci
> card1                   8086:4905    pci:vendor=8086,device=4905,card=0
> └─renderD129
> card0                   8086:3E98    pci:vendor=8086,device=3E98,card=0
> └─renderD128
> 
> Or two identical GPUs (mocked by manual addition of an almost duplicate
> entry to list of scanned devices:
> 
> $ tools/lsgpu --pci
> card0                   8086:193B    pci:vendor=8086,device=193B,card=0
> ├─renderD128
> └─renderD128
> card0x                  8086:193B    pci:vendor=8086,device=193B,card=1
> ├─renderD128
> └─renderD128
> 
> Regards,
> 
> Tvrtko

I made a mistake in above listing, it should be:
/sys/devices/pci0000:00/0000:00:04.0	-> vendor 8086, device 1234	pci_index == 0
/sys/devices/pci0000:00/0000:00:05.0	-> vendor 8086, device 4321	pci_index == 0
/sys/devices/pci0000:00/0000:00:06.0	-> vendor 8086, device 1234	pci_index == 1

What if I would go over all Intel cards using pci filter:

pci:vendor=8086,card=N   where n is 0... until there's no Intel pci device.

This way we loose possibility to iterate over all pci devices imo.

--
Zbigniew