On Sat, Jun 04, 2016 at 08:32:43PM +0200, Michał Pecio wrote: > Hi, > > Why high-bandwidth USB 1.1 isochronous devices don't work on 2.0 hosts? > > I have an ADSL modem of this kind which I would like to use on a > companion-less 2.0 host in my router, but I can't because it fails with > ENOSPC errors. Same thing happens on my PC when connected through a 2.0 > hub, but it works perfectly on 1.1 and 3.0 hosts, with or without hubs. > > This seems to be an old and widely known issue, but the only "solution" > I found so far is "well, just don't use hubs and let the companion take > it over", which obviously doesn't solve the case of pure-EHCI SoCs. > > (Well, another solutions applicable to those particular modems is to > switch them to bulk mode, but it's slower.) > > Is this some limitation of the USB 2.0 spec or just a Linux issue? > > Any possible fixes or hackarounds? Don't use a 2.0 hub, or connect it directly as you have, or use a 3.0 controller :) Seriously, handling 1.1 transactions through a 2.0 hub is hard, and messy. It's been a known issue for decades, and given that 3.0 pretty much resolved most of these issues, no one is working to resolve them anymore, it's just so much simpler to change hardware. sorry, greg k-h -- 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
