Alan Stern wrote:
At this point, only "uhci-hcd" relies on that and I have a note somewhereThis is where my lack of knowledge of the details underlying the usb core shows through. Okay, looking at hcd.c I see where urb_unlink() is called and how it releases the bandwidth. I'm surprised; is it really supposed to work this way?
that it doesn't actually reserve such bandwidth correctly. The basic
problem is that the model of those bandwidth reservation calls is wrong.
(Especially so for ISO ... consider that two queued ISO requests will
get accounted as twice the bandwidth of one, rather than just one
being used serially...)
As for the other posts on this thread, I hope to have time to read
them later. Adding more spinlocks is (more often than not) a Bad Thing,
deadlock-prone. It's not clear to me why urb->lock wouldn't suffice,
and there's some other wierdness being proposed.
- Dave
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