linux-kernel - Re: [PATCH] lis3lv02d: provide means to disable polled input interface

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Date:	Fri, 09 Apr 2010 15:29:53 +0200
From:	Éric Piel <eric.piel@...mplin-utc.net>
To:	Jiri Kosina <jkosina@...e.cz>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Samu Onkalo <samu.p.onkalo@...ia.com>,
	Pavel Machek <pavel@....cz>, lm-sensors@...sensors.org,
	linux-kernel@...r.kernel.org,
	Marcin Derlukiewicz <marcin@...lukiewicz.pl>
Subject: Re: [PATCH] lis3lv02d: provide means to disable polled input interface

On 09/04/10 14:56, Jiri Kosina wrote:
> lis3lv02d driver creates emulated joystick interface for events reported 
> by the sensor.
> Because of HW, this has to be implemented as polled input device, with
> 20Hz frequency.
> 
> This is reported to create 20% CPU usage increase (and proportionaly higher
> power consumption) just for the ipolldevd kernel thread (which is used
> to read the sensor).
> 
> As most users probably only use the freefall functionality of the driver
> and not the joystick interface, provide means for disabling the registration
> of joystick device altogether via module parameter.
> (I'd rather make it default to 0, but this will break backwards compatibility).
Are you saying there is a 20% CPU usage even when the joystick interface
is not open? This should not happen (and this is not happening on my
laptop). The polling should happen only when a userspace app opens the
joystick interface (like running neverball).

So I'd tend to think it's more due to a misconfiguration of the system
(like xserver using the joystick interface as a pointer device) or it's
a bug in the way we set up the polling. Could you investigate and let me
know?

Cheers,
Eric
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