linux-kernel - Re: [PATCH] USB: Only enable autosuspend by default on certain device classes

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Date:	Fri, 3 Aug 2007 15:33:38 +0100
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	David Brownell <david-b@...bell.net>,
	Rogan Dawes <lists@...es.za.net>,
	Oliver Neukum <oliver@...kum.org>, Greg KH <gregkh@...e.de>,
	linux-usb-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] USB: Only enable autosuspend by   default on certain device classes

On Fri, Aug 03, 2007 at 10:28:19AM -0400, Alan Stern wrote:
> On Fri, 3 Aug 2007, Matthew Garrett wrote:

> There are two possible solutions, both involving the kernel (since
> userspace can't respond in time).  One is to change the default timeout
> to something larger, or even disable it completely.  Then people would
> need to rely on userspace tools to enable autosuspend on known-good
> devices.  The other possibility is to have a fairly reliable blacklist
> or whitelist and again rely on userspace to manage edge cases.  This is 
> of course more flexible than a blanket default setting, but it's still 
> pretty rigid.  On the other hand, a blacklist can't be changed without 
> rebuilding the kernel whereas the default timeout can be adjusted on 
> the boot command line.

Windows will autosuspend hubs, bluetooth devices, HID devices and CDC 
devices, so I think we're safe suspending those by default. I'm not so 
enthusiastic about the "Increase the timeout case" - it doesn't avoid 
any races, just makes them less likely. USB is likely to get loaded in 
the initramfs, but we may not have a full set of udev rules until the 
root fs is up and that can take an effectively arbitrarily large amount 
of time.

-- 
Matthew Garrett | mjg59@...f.ucam.org
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