linux-kernel - Re: [PATCH RFC] USB: Add HCD fastboot

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Date:	Wed, 06 Aug 2008 20:20:13 +0100
From:	Simon Arlott <simon@...e.lp0.eu>
To:	Alan Stern <stern@...land.harvard.edu>
CC:	Rene Herman <rene.herman@...access.nl>,
	Arjan van de Ven <arjan@...radead.org>,
	linux-kernel@...r.kernel.org, mingo@...e.hu,
	Daniel Walker <dwalker@...sta.com>,
	USB list <linux-usb@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: Re: [PATCH RFC] USB: Add HCD fastboot

On 06/08/08 20:11, Alan Stern wrote:
> On Wed, 6 Aug 2008, Simon Arlott wrote:
> 
>> On 31/07/08 20:16, Alan Stern wrote:
>> >> > It's not entirely clear why usblp is blocking at all.  Probably because
>> >> > it is waiting on the device semaphores for devices that are currently
>> >> > being probed -- the driver core won't allow two threads to probe the
>> >> > same device concurrently.
>> >> 
>> >> Ok - so there could be some big improvements to be had by making the hcd 
>> >> init happen as early as possible and the device initcalls later?
>> > 
>> > Maybe.  Perhaps a better approach would be to make the device driver 
>> > initcalls before there are any devices for their probe routines to 
>> > block on.
>> 
>> What about this?
>> 
>> The Makefiles become a bit messy, but by moving things around I get the 
>> desired effect without splitting their initcalls.
> 
> Wouldn't it be much simpler, and less objectionable, to do what I
> suggested earlier?  That is, add a 5-second delay at the start of
> hub_thread() in drivers/usb/core/hub.c.  No messing with Makefiles, no
> changes to the initcall scheduling.

Aside from 5 seconds being too long, and anything less being a race between 
hub_thread() and driver initcalls, it doesn't improve anything because it'll 
still have to wait for the devices to finish initialising in userspace instead.

-- 
Simon Arlott
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