I am fairly certain the problem is not related to sharing the USB bus. I had four of those converters connected to an ordinary USB hub working 100% reliably, as long as USB 2.0 was disabled. Plus, you can buy a fairly expensive (hundreds of $) multi-port converter which internally is nothing more than a couple of cascaded USB hubs and pl2303 chips. I hope that they wouldn't be selling such devices if the underlying chip was fundamentally broken. Lastly, it all works peachy in Windows. I tried USB_EHCI_TT_NEWSCHED (it is included in 2.6.22), but it didn't fix it. Alas I didn't have the chance to dig too deep (and I am not an USB expert, although I have done kernel programming) - sometimes it took many hours to reproduce the errors, and using USB 1.1 solved my immediate problem. When I saw Greg KH's explanation that there are problems in the USB 2.0 implementation known for for years, I lost my hope of improving the situation constructively. Perhaps I should pick it up again. What is the best forum to report this problem ? Apparently not the kernel Bugzilla ? :-)
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