linux-kernel - Re: usb: why we need a msleep(5) in ehci_bus

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Date:	Mon, 13 May 2013 10:15:32 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	linux fddl <fddllinux@...il.com>
cc:	linux-usb@...r.kernel.org, <gregkh@...uxfoundation.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: usb: why we need a msleep(5) in ehci_bus_suspend/resume

On Mon, 13 May 2013, linux fddl wrote:

> Hi,
> 
>   From the ehci-hub.c, I find that ehci_bus_suspend/resume have some
> code like this:
> 
> if (time_before(jiffies, ehci->netx_statechange))
>     msleep(5);
> ...
> ehci->next_statechange = jiffies + msec_to_jiffies(10);
> 
> and
> 
> if (time_before(jiffies, ehci->netx_statechange))
>     msleep(5);
> ...
> ehci->next_statechange = jiffies + msec_to_jiffies(5);
> 
> but I don't know why such a short sleep is needed, and why one is
> [ehci->next_statechange = jiffies + msec_to_jiffies(10)] and the other is
> [ehci->next_statechange = jiffies + msec_to_jiffies(5)],
> I googled for a long time, but it seems that there is no explanation.
> 
>   Anyone knows why and can give any explanation?

At this point I don't think anybody knows.  The person who originally
wrote that code died a few years ago.

Alan Stern

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