Messages in this thread | | | Date | Thu, 8 Oct 2009 10:58:39 -0400 (EDT) | From | Alan Stern <> | Subject | Re: [PATCH 4/5] usb_serial: Kill port mutex |
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On Thu, 8 Oct 2009, Oliver Neukum wrote:
> Am Mittwoch, 7. Oktober 2009 23:34:12 schrieb Alan Stern: > > I'm losing track of the original point of this thread. IIRC, the > > problem is how the resume method should know whether or not to submit > > the receive URB(s). It can't afford to acquire the port mutex because > > it might be called by open or close, at which time the mutex is already > > held. > > > > 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.
> 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.
Alan Stern
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