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

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Message-ID: <Pine.LNX.4.44L0.0910071233240.2762-100000@iolanthe.rowland.org>
Date:	Wed, 7 Oct 2009 12:34:55 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Oliver Neukum <oliver@...kum.org>
cc:	Alan Cox <alan@...ux.intel.com>, <greg@...ah.com>,
	<linux-kernel@...r.kernel.org>, <linux-usb@...r.kernel.org>
Subject: Re: [PATCH 4/5] usb_serial: Kill port mutex

On Wed, 7 Oct 2009, Oliver Neukum wrote:

> Am Mittwoch, 7. Oktober 2009 18:03:08 schrieb Alan Stern:
> > On Wed, 7 Oct 2009, Oliver Neukum wrote:
> > > We will need some generic way to autoresume from open.
> > > Resume will need to lock against open() and need to be called
> > > from within open(). Any ideas for an unugly interface?
> >
> > It's not quite that bad.  Resume doesn't need to lock against open.
> > If open is called while resume is running then when it tries to do its
> > own resume, it will either block (waiting for the pm_mutex) or return
> > immediately (if it sees the device is already resumed).
> 
> But resume() needs to know whether the read URBs need to be
> submitted or not.

Given that there are several pathways for turning on or turning off the 
read URBs, the best answer is to use a flag.

Alan Stern

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