linux-kernel - Re: [RFC][PATCH v2 06/13] usb: hcd: Add hcd add/remove functions for OTG use

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Message-ID: <Pine.LNX.4.44L0.1504200948280.1321-100000@iolanthe.rowland.org>
Date:	Mon, 20 Apr 2015 09:56:40 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Roger Quadros <rogerq@...com>
cc:	Peter Chen <peter.chen@...escale.com>,
	<gregkh@...uxfoundation.org>, <balbi@...com>,
	<dan.j.williams@...el.com>, <jun.li@...escale.com>,
	<mathias.nyman@...ux.intel.com>, <tony@...mide.com>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-omap@...r.kernel.org>
Subject: Re: [RFC][PATCH v2 06/13] usb: hcd: Add hcd add/remove functions
 for OTG use

On Mon, 20 Apr 2015, Roger Quadros wrote:

> > I don't understand this.  Why do you want to defer the add/remove if 
> > the device is OTG?  Don't host controller drivers expect these things 
> > to execute synchronously?
> 
> Sorry for the wrong information. We actually defer only the add as the
> OTG state machine might not yet be in Host ready mode.
> The remove is always synchronous and we ensure that the HCD is removed
> when usb_otg_unregister_hcd() returns.

That's okay then, but it does leave one potential hole.  What happens 
if usb_add_hcd() is deferred for so long that usb_remove_hcd() gets 
called before the add can complete?

Alan Stern

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