linux-kernel - Re: [PATCH 1/3] Input: Fixed ABS_MT_TOUCH_MINOR scale factor in BCM5974 multitouch driver

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Date:	Thu, 21 Nov 2013 10:05:01 +0100
From:	Henrik Rydberg <rydberg@...omail.se>
To:	Friedrich Schöller <linux@...oeller.se>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	linux-input@...r.kernel.org
CC:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] Input: Fixed ABS_MT_TOUCH_MINOR scale factor in BCM5974
 multitouch driver

Hi Friedrich,

> On wellspring3 devices ABS_MT_TOUCH_MINOR was sometimes reported bigger than
> ABS_MT_TOUCH_MAJOR. This is fixed by rescaling ABS_MT_TOUCH_MINOR by a factor of
> 0.85 instead of 2. Excessive tapping on the trackpad shows this to be the right
> value. Circular touches should now lead to values for ABS_MT_TOUCH_MAJOR and
> ABS_MT_TOUCH_MINOR that are similar, with ABS_MT_TOUCH_MINOR never greater than
> ABS_MT_TOUCH_MAJOR.
> ---
>  drivers/input/mouse/bcm5974.c | 20 +++++++++++++++++---
>  1 file changed, 17 insertions(+), 3 deletions(-)

The major/minor scales are following the aspect ratio of the device, and as such
it could happen that minor > major. Most userland drivers do not use the finger
width limits, which are estimates, but only the device axes limit, which are
accurate.

Also, we cannot have floats in the kernel.

I would consider a patch which tries to make the finger widths more accurate,
but all in all, I think this problem is best solved in userland.

Thanks,
Henrik

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