On Wed, 13 Sep 2017, Nikola Ciprich wrote: > Hi fellow linux USB users and developers, > > we've spent lots of time trying to resolve issue with very little > progress so I'd like to try asking for help here.. > > we're migrating big amount of users from SUSE running i386 2.6.13 > kernel to x86_64 centos-based system running x86_64 4.4.x kernel > (tried 4.13 as well). > > many machines are deployed with symbol (zebra?) DS6708 barcode readers > and after machine boot, it is often not working, either not lit at > all, or not scanning correctly. Unplugging/plugging the reader solves > the issue. (machines are various types of Lenovo desktops) There are devices like this. They only work under certain conditions. I have a USB disk drive enclosure which works okay if you power it up and then plug the USB cable into the computer, but not if you do these things in the opposite order. > Our guess is it has something to do with power, as using the ammeter > it seems that when the device is not working, it just takes very little > current, so maybe it just doesn't "tell" the bus to increase voltage > at start? > > A colleague has developped solution to fix on ehci-hcd managed ports > using unbind/bind of the particular device, so we can "fix" it automatically > on boot. However it doesn't work/help on other USB buses, ie uhci-hcd > or xhci-hcd (this is on new models and was not been used on SUSE at all) > > Sometimes reloading usb module helps, but sometimes not. > > My question is, did somebody have/solve similar issue? Is there a way > to decrease/increase power in generic way, so I can subsctitute device > unplug/plug? Or maybe some even better any better way I could use to > solve this issue? There are hundreds of those readers in production, > so replacing them is a problem.. One possibility is to plug the reader into a hub with true port-power switching. (Lots of hubs don't have power switching on their ports, but some models do.) Then you will be able to run a program after boot that will turn off power to the hub's ports and then turn it back on. Most desktop and laptop computers are not able to turn off power to their USB ports. 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
