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

From: Adam Kropelin
Date: Fri Aug 03 2007 - 11:26:46 EST


Dave Jones wrote:
On Fri, Aug 03, 2007 at 04:43:16PM +0200, Jiri Kosina wrote:
On Fri, 3 Aug 2007, Matthew Garrett wrote:

Windows will autosuspend hubs, bluetooth devices, HID devices

Hi Matthew,

are you sure about windows suspending the HID devices in runtime? I
have never seen LEDs of USB keyboard connected to windows host to go
off after some time of not using it.

Not so sure about keyboards, but I've seen the LEDs on USB mice dim
or go off after a few seconds of inactivity under Windows, but under
Linux they stay on.

We have been playing with runtime autosuspend of HID devices, are
currently postponed the full support, as it turns out that many
devices don't support this feature properly (probably due to not
being tested in Windows).

Interesting. Which devices did you notice failing?
Was it a case that they would sleep and not come back out of that
state?

Although I have no proof immediately at hand, I suspect at a minimum HID power class devices should be blacklisted from autosuspend. Given the spotty USB implementations on many such devices I'd be surprised if suspend worked reliably. Plus if you're connected to such a device for monitoring purposes you're probably powered by it as well, so you have little to gain from suspend even if it works.

--Adam

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