2005/9/12, Alan Stern <[EMAIL PROTECTED]>:
> No, it means there's a mistake in urb_unlink. It should not release
> the bandwidth reservation. Even if the HCD calls claim_bandwidth again
> after giveback_urb returns, there's still a period of time while the
> completion routine is running during which the bandwidth information is
> wrong.
ok I guess it will be fixed when bandwidth rework will start.
>
> You should return 0. That just means your driver knows that the URB has
> been dequeued; it doesn't mean you've already called giveback_urb.
>
> In fact, you should always return 0. (The dequeue method really should be
> declared as returning void, not int.) However, your _enqueue_ routine
> should check urb->status and return an error if it isn't equal to
> -EINPROGRESS. This can happen if a second thread tries to unlink an URB
> before the first thread has finished submitting it:
>
> Thread 1 Thread 2
> -------- --------
> Calls usb_submit_urb
> -> hcd_submit_urb
> Sets urb->status = -EINPROGRESS
> Gets as far as the
> spin_unlock_irqrestore line
> Calls usb_unlink_urb
> -> hcd_unlink_urb
> sets urb->status to -ENOENT or
> -EDISCONN
> -> your dequeue routine
> Nothing to do: not yet queued
> -> your enqueue routine
> Return an error; already unlinked
> since urb->status != -EINPROGRESS
>
> To be fair, you don't _have_ to do things this way. It would be equally
> valid to have both your enqueue and dequeue routines return 0 in this
> situation. But then your enqueue routine would have to know that it
> shouldn't fully queue the URB; it should set things up so that at the next
> interrupt the URB will be sent to giveback_urb. That's a bit more work.
>
Thanks for these usefull explanations ! I have another question ;)
urb->error_count is documented (in kernel code)as follows: "Returns
the number of ISO transfers that reported errors." For not ISO
transfers can I use it for my own purposes ?
Thanks again
--
Franck
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