linux-kernel - Re: [PATCH] usb: generic calibration support

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Message-Id: <200611170024.33248.daniel.ritz-ml@swissonline.ch>
Date:	Fri, 17 Nov 2006 00:24:32 +0100
From:	Daniel Ritz <daniel.ritz-ml@...ssonline.ch>
To:	Holger Schurig <hs4233@...l.mn-solutions.de>
Cc:	daniel.ritz@....ch, linux-kernel@...r.kernel.org,
	linux-usb-devel@...ts.sourceforge.net,
	Dmitry Torokhov <dmitry.torokhov@...il.com>
Subject: Re: [PATCH] usb: generic calibration support

hi

On Thursday 16 November 2006 11.25, Holger Schurig wrote:
> From: Holger Schurig <hs4233@...l.mn-solutions.de>
> 
> Generic calibration support for usbtouchscreen.
> 
> Signed-off-by: Holger Schurig <hs4233@...l.mn-solutions.de>
> 
> ---
> 
> With build-in calibration support, the "swap_xy" kernel parameter
> vanishes and usbtouchscreen instead gains a new kernel-parameter
> which holds 7 integers.
> 
> This is used to calibrate the resulting output of the driver. Let
> x_o and y_o be the original x,y coordinate, as reported from the
> device. Then x_r,y_r (the x,y coordinate reported to the input event
> subsystem) are:
> 
>     x_r = ( a*x_o + b*y_o + c ) / s
>     y_r = ( c*x_o + d*y_o + e ) / s
> 
> The default values for (a,b,c,d,e,s) are (1,0,0,0,1,0,1). To
> simulate swap_xy, one would set them to (0,1,0,1,0,0,1). Once can
> also use swap_x or swap_y alone, or define other, linear
> transpositions. The algorithm used is the same as in Qt/Embedded
> 3.x for the QWSCalibratedMouseHandler.
> 
> This interface allows re-calibration at runtime, without
> restarting the X-Server or any other event consumer.
> 
> 
> Please review this patch and schedule it for inclusion once 
> 2.6.19 comes out.

sorry, but i have to give you a big NACK on that one:
- no more modparam: it should be per-device sysfs attributes
  (swap_xy is basically only for touchkitusb compatibility and shoud be
   converted to per-device sysfs attribute as well. i just never got to
   do it)
- calibration can be handled in userspace just fine
- even for in-kernel it's in the wrong place. there are other devices
  that report raw absolute data...so it would belong to the input layer

Cc'ing Dmitry Torokhov as he might have some comments about calibration
support in the input layer.

thanks, rgds
-daniel
-
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