linux-kernel - Re: [PATCH][RFC] usbhid: enable autosuspend for internal devices

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Date:	Mon, 29 Jun 2015 11:48:12 +0200
From:	Oliver Neukum <oneukum@...e.com>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Tom Gundersen <teg@...m.no>, linux-usb@...r.kernel.org,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][RFC] usbhid: enable autosuspend for internal devices

On Sat, 2015-06-27 at 08:29 +0200, Jiri Kosina wrote:
> On Fri, 26 Jun 2015, Greg Kroah-Hartman wrote:

> Last time we were testing this, autosuspend for USB HID devices was quite 
> a disaster.
> 
> Do you have any idea whether udev developers tested the "autosuspend on by 
> default for USB HID devices" on reasonable set of devices?
> 
> The culrpits that I remember from top of my head (it's been long time 
> ago):
> 
> - the LEDs for suspended device go off. This is very confusing at least on 
>   keyboards, and brings really bad user experience

That is a bug. hidinput_count_leds() is supposed to prevent that.
What did you test?

> - many keyboards were losing first keystroke when waking up from suspend. 
>   We've been debugging this with Alan, and never root-caused it to a 
>   problem in our code, it seems to be the property of the HW

- mice don't wake up from movement alone.

And again I would state that we don't get enough information
from user space. Hardware seems to be designed for sleeping
while a screen saver is on. In kernel space we just get a binary
input desired or not desired from open/close.
That is insufficient.

	Regards
		Oliver



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