linux-kernel - Re: [PATCH] Input: evdev - use monotonic clock for event timestamps

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Message-ID: <20111005092341.GB6840@polaris.bitmath.org>
Date:	Wed, 5 Oct 2011 11:23:41 +0200
From:	"Henrik Rydberg" <rydberg@...omail.se>
To:	Daniel Kurtz <djkurtz@...omium.org>
Cc:	dmitry.torokhov@...il.com, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Input: evdev - use monotonic clock for event timestamps

> I understand your concern about breaking random drivers, and am hoping
> that someon on this list could indicate whether this is a real concern
> or not.  To get a better feeling for possible regressions, I checked
> xf86-input-evdev & -synaptics, and neither uses the evdev timestamp in
> their current incarnations.  Any idea what else might be a good place
> to check?

The input system is used for all sorts of events - switches, for
instance. The point is that it is nearly impossible to know if
something will break or not, hence the reluctance to modify interfaces.

> One option is to make the evdev timestamp clock source a per-driver
> configuration option (controllable from userspace?).  This sounds like
> it is doable, but would be significantly more complicated.
> 
> Another option would be to timestamp with monotonicraw + boottime +
> sleeptime.  This would be approximately wall clock time, but without
> ntp and slew adjustments.  But, I fear this would just make the rare
> driver issue less obvious, since it would only become obvious when the
> two clock sources started drifting apart.

I agree, the problem is not really solvable. Dmitry?

Thanks,
Henrik
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