Hm, I can't seem to get a USB 1.1 device to work through a 2.0 hub plugged into a 2.0 controller. I get a -ENOSPC error when trying to submit an interrupt urb. But this happens without your patch, so this is probably an old bug. I'll look into it in a few days when I get a chance...
My first guess would be the long-standing restrictions on how much of the reserved bandwidth will be used ... the driver significantly undercommits, allows only one interrupt transaction per frame. (Rather than hundreds...)
The simple workaround is to make sure the devices use longer periods (one frame is killer, four or eight tend to work ok). It's usually no real problem to have multiple hubs, mice, or keyboards ... but some device combos may have trouble.
I sent an experimental patch around a while back, which teaches EHCI to build an interrupt schedule tree (like OHCI does), with (necessary) TT scheduling. You might see if that helps.
- Dave
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