On Thu, 20 Mar 2014, Alejandro Exojo wrote: > 2014-03-20 10:52 GMT+01:00 Peter Stuge <peter@xxxxxxxx>: > > I understand the expectation, but I don't think Linux meets it. > > > > The difference in your logs is the usbX bus number, which really can > > not persist beyond the lifetime of that bus. > > > > Think of a laptop with a CardBus slot. CardBus is just PCI. If you > > plug a USB host card into that laptop, which number will the new usbX > > bus have? > > > > What if that same card is plugged in during boot? > > > > What if the card is unplugged? The usbX goes away. And then the card > > is plugged back in. A new usbX comes in. X is only valid for the > > lifetime of that bus. For soldered-on buses like in the chipset this > > means until reboot. > > OK. I don't fully understand the details, but I think I got your point. > > > I think your best chance is to filter out the usbX bus name yourself. > > > > E.g. match on the DEVPATH prefix /devices/pci0000:00/0000:00:1d.7/ > > and on the suffix -4.1:1.0/usbmisc/pcanusb* > > That seems good enough to make an udev rule, I will try ASAP. :-) > > > That will always match the same pcanusb device plugged into the same > > physical port, as long as chipset or firmware (BIOS upgrade) does not > > remap PCI devices and/or device functions. While hardware might > > support such remapping, in particular if the hardware is virtualized, > > as is increasingly the case, devfns changing is rare. But you do need > > to coordinate this with whoever is your BIOS engineer if you want > > actual reliability. > > Ok, we will have that into account. I think it will be acceptable with > our little knowledge on the issue. > > > Thank you very much! We've struggled quite a bit with this. A more general approach is to match based on the vendor and product IDs, and perhaps also on the serial number (except that lots of devices don't define meaningful serial nunbers). That way, it doesn't matter what port a device is plugged into. For example, if you can match simply on "pcanusb", that would probably be best. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
