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 16:35:52 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Simon Arlott <simon@...e.lp0.eu>
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 Sat, 19 Jul 2008, Simon Arlott wrote:

> 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?

In fact it will, to a large extent.  The new code isn't present in
2.6.26 but it ought to be in 2.6.27-rc1.

However Arjan wasn't talking about debounce delays; he was talking 
about port-power-on delays.  A nice improvement would be to combine the 
two types of delay into one.  I'll look into it...

Alan Stern

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