Re: [PATCH 4/5] usb_serial: Kill port mutex

[Oliver Neukum <oliver@neukum.org>]

Am Donnerstag, 8. Oktober 2009 16:58:39 schrieb Alan Stern:
> On Thu, 8 Oct 2009, Oliver Neukum wrote:
> > Am Mittwoch, 7. Oktober 2009 23:34:12 schrieb Alan Stern:

> > > Other schemes could work, but to me it seems simplest to rely on a flag
> > > protected by a spinlock.  The flag would mean "URBs are supposed to be
> > > queued unless we are suspended".  It would be set by open and
> > > unthrottle, and cleared by close and throttle.
> >
> > 1. Why a spinlock?
>
> Because the amount of work involved seems too small for a mutex.  But
> you could use a mutex if you wanted, since everything occurs in process
> context.

We have to submit URBs under that lock.

> > 2. Can we get by with only one flag?
>
> If all you want to do is answer a single question ("Should URBs be
> submitted") then a single flag should be all you need.  Why, do you
> think more information will be necessary?  You can always add more.

We have at least three reasons URBs should not be submitted.
- closure
- throttling
- suspension
Resume() should not submit if either closure or throttling are active,
neither should unthrottle() resubmit if closure or suspension are active.

	Regards
		Oliver