linux-kernel - Re: Logitech autosuspend + runtime

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Date:	Sat, 5 Feb 2011 15:14:12 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Andrew Lutomirski <luto@....edu>
cc:	linux-kernel@...r.kernel.org, <linux-usb@...r.kernel.org>,
	pm list <linux-pm@...ts.linux-foundation.org>
Subject: Re: Logitech autosuspend + runtime_pm loses input

On Sat, 5 Feb 2011, Andrew Lutomirski wrote:

> I have a Logitech MX Revolution (a cordless mouse receiver) plugged
> into a Logitech G15 (a keyboard w/ a hub) plugged into an Intel Cougar
> Point EHCI controller.  (Results are the same on an xHCI controller,
> though.)
> 
> With autosuspend *or* runtime PM off, everything works.  (Well, the
> G15 is buggy and occasionally crashes and doesn't recover until
> powercycled, but that even happens on Windows.)  With runtime PM
> enabled on the whole tree, I have problems with autosuspend.
> 
> If I enable autosuspend on just the mouse by doing:
> 
> echo 2 >./1-1/1-1.2/1-1.2.3/power/autosuspend
> (where that device is Bus 001 Device 005: ID 046d:c51a Logitech, Inc.
> MX Revolution/G7 Cordless Mouse), then after about two seconds of not
> moving the mouse, the mouse ignores the first second or so of motion
> when I start moving it again.
> 
> If I enable autosuspend on just part of the keyboard by doing:
> 
> echo 2 >./1-1/1-1.2/1-1.2.1/power/autosuspend
> (that's Bus 001 Device 004: ID 046d:c221 Logitech, Inc. G11/G15
> Keyboard / Keyboard)
> 
> then after a couple seconds of not typing, my next keystroke is lost or delayed.
> 
> It seems to be enough to turn off runtime PM (via power/control) OR
> turn off autosuspend on the keyboard device to make the keyboard work
> and on the mouse device to make the mouse work.
> 
> Is this a case of "don't do that, you fool," or is there a legitimate
> bug to be fixed in the runtime pm code?
> 
> My motherboard is Intel DH67GD (ordered just before they canceled
> production) with latest BIOS.

I don't think there is any bug in the code.  The problem lies in the 
devices; they appear to be designed so as to lose some input events 
when waking up from suspend.  This is very common among keyboard and 
mouse devices -- probably because autoresume was not used under Windows 
and hence didn't get tested.

Hence my advice is, as you guessed, "Don't do that".

Alan Stern

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