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

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Message-ID: <Pine.LNX.4.44L0.0910071157390.2762-100000@iolanthe.rowland.org>
Date:	Wed, 7 Oct 2009 12:03:08 -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:

> 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).

A more interesting question is how to synchronize both open/close and
suspend/resume against throttle/unthrottle.

Alan Stern

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