> Here's another possibility. For each usb_device we include a
> pre-allocated URB, together with a usb_ctrlrequest and a 64-byte buffer.
> This URB could be used while holding the device lock, for things like
> get_descriptor, suspend, or reset.
Good idea.
> > An URB with its buffer preallocated is bound to a device, respectively
> > an endpoint, so it cannot complete without triggering the same irq the
> > completion handler is running in.
>
> Ah yes. Although I would prefer to make each URB & buffer bound to a
> HC/bus, not to a device or endpoint -- but that doesn't affect your point.
Why? Drivers cannot share URBs among interfaces, unless you export
the concept of busses, which would violate layering.
Furthermore to a driver the interface is the natural unit of operation.
And the more specific an URB is the less usb_submit_urb() has to do.
> This would allow us to replace an atomic_t with an unsigned long and use
> bit-operations rather than atomic_inc/atomic_dec. It would improve
> performance on the Sparc platform and wouldn't make much difference
> anywhere else.
Indeed one bit would be enough.
Regards
Oliver
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