linux-kernel - Re: Re [patch 2/3] fastboot: turn the USB hostcontroller initcalls into async initcalls

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Date:	Sat, 19 Jul 2008 16:32:20 +0100
From:	Simon Arlott <simon@...e.lp0.eu>
To:	Alan Stern <stern@...land.harvard.edu>
CC:	Arjan van de Ven <arjan@...radead.org>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	USB list <linux-usb@...r.kernel.org>
Subject: Re: Re  [patch 2/3] fastboot: turn the USB hostcontroller initcalls
 into async initcalls

On 19/07/08 16:25, Alan Stern wrote:
> On 18 July, 2008, Arjan van de Ven wrote:
> 
>> From: Arjan van de Ven <arjan@...ux.intel.com>
>> Subject: [PATCH] fastboot: turn the USB hostcontroller initcalls into 
>> async initcalls
>> 
>> the USB host controller init calls take a long time, mostly due to a
>> "minimally 100 msec" delay *per port* during initialization.
>> These are prime candidates for going in parallel to everything else.
>> 
>> The USB device ordering is not affected by this due to the
>> serialized-within-eachother property of async initcalls.
> 
> Is there some reason this patch wasn't posted to the linux-usb mailing
> list as well as to LKML?
> 
> Where is this "minimally 100 msec" per-port delay you refer to?  
> Offhand I can't recall any such delays in the init routines.
> 

usb/core/hub.c:

/* USB 2.0 spec, 7.1.7.3 / fig 7-29:
 *
 * Between connect detection and reset signaling there must be a delay
 * of 100ms at least for debounce and power-settling.  The corresponding
 * timer shall restart whenever the downstream port detects a disconnect.
 *
 * Apparently there are some bluetooth and irda-dongles and a number of
 * low-speed devices for which this debounce period may last over a second.
 * Not covered by the spec - but easy to deal with.
 *
 * This implementation uses a 1500ms total debounce timeout; if the
 * connection isn't stable by then it returns -ETIMEDOUT.  It checks
 * every 25ms for transient disconnects.  When the port status has been
 * unchanged for 100ms it returns the port status.
 */

Could it do that for all ports on the hub in parallel instead?

-- 
Simon Arlott
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