Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758866AbZJHQ6q (ORCPT ); Thu, 8 Oct 2009 12:58:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758550AbZJHQ6p (ORCPT ); Thu, 8 Oct 2009 12:58:45 -0400 Received: from iolanthe.rowland.org ([192.131.102.54]:33099 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751657AbZJHQ6o (ORCPT ); Thu, 8 Oct 2009 12:58:44 -0400 Date: Thu, 8 Oct 2009 12:58:08 -0400 (EDT) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: Oliver Neukum cc: Alan Cox , Greg KH , Kernel development list , USB list Subject: Re: [PATCH 4/5] usb_serial: Kill port mutex In-Reply-To: <200910081727.11745.oliver@neukum.org> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1651 Lines: 44 On Thu, 8 Oct 2009, Oliver Neukum wrote: > 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. Yes. What's your point? > > > 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. True. Nor should open() submit if throttling is active. Feel free to use three separate flags. :-) Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/