linux-kernel - Re: [PATCH v4 14/14] HID: hid-multitouch: forwards MSC

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Message-ID: <20121120205147.GA4658@polaris.bitmath.org>
Date:	Tue, 20 Nov 2012 21:51:47 +0100
From:	"Henrik Rydberg" <rydberg@...omail.se>
To:	Benjamin Tissoires <benjamin.tissoires@...il.com>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Jiri Kosina <jkosina@...e.cz>,
	Stephane Chatty <chatty@...c.fr>, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 14/14] HID: hid-multitouch: forwards MSC_TIMESTAMP

Hi Benjamin,

> > In addition, it would make perfect sense to extend the validity of the
> > hardware time with the event time for longer intervals. The relative
> > error only makes a difference on milisecond intervals.
> >
> > A patch that seamlessly extends the validity of the hardware time,
> > ideally using the event time, seems like a viable solution.
> 
> Just to be sure:
> When I receive scan_time, I increment timestamp with the device value.
> When not, I find out the number of counter wrap I missed with the
> kernel timer (jiffies) to get the actual device time.
> 
> Is that ok for you?

If the device has no scan time, then no scan time is reported, of
course.  If the scan time delta _and_ the actual time delta are both
below logical_max (say), then increase the counter with the scan time
delta. Else, if the actual time delta is below 2^31, increase the
counter with the actual time delta. Else set the counter to zero.

This ought to give us the sought-after accuracy for small times, the
sought-after extension for intermediate times, and a clear definition
of unknown time.

Cheers,
Henrik
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