Re: [PATCH 2/5] input: wacom - remove pressure for touch devices

On Wed, Aug 17, 2011 at 08:32:28AM -0700, Ping Cheng wrote:

On Tue, Aug 16, 2011 at 11:50 PM, Dmitry Torokhov <dmitry.torokhov@gmail.com

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wrote:

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On Mon, Aug 15, 2011 at 09:34:23PM -0700, Ping Cheng wrote:

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On Sun, Aug 14, 2011 at 8:27 PM, Chris Bagwell [off-list ref]

wrote:

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On Fri, Aug 12, 2011 at 7:08 PM, Ping Cheng [off-list ref]

wrote:

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Touch devices do not report valid pressure or capacitance.

Signed-off-by: Ping Cheng <redacted>
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I'd prefer if we kept pressure support.  At least for Bamboo's with
product ID between 0xd0 and 0xd4.

In my testing of an 0xd1 device, pressure works fine (low pressure and
high pressure work great.  Not much middle pressure sensitivity.
Multi-touch will increase pressure reading.  All pretty common
behaviour).

Basically, there were three reasons to remove the pressure bit for all

touch

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devices:

1.   The value is not a pressure and it does not report valid capacitance
either;
2.   The only valid use in the kernel driver is to decide if the finger

is

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touching the tablet or not, which has already been correctly reported by

the

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firmware in the other bits. So, it is redundant to check the pressure for
this purpose;
3.   Passing the invalid "pressure" to the user land would only introduce
bad user experience since touch is not designed for drawing. We don't

want

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to confuse user with that "pressure".

Not speaking about touch per se, but pressure is important for other
things besides drawing. Different people prefer different device
sensitivity and if userspace knows pressure it can adjust according to
user preference, like synaptics X driver does with touchpads that
actually report it. I believe tslib allows similar for touchscreens.

Your suggestion is based on the assumption that the value is pressure.

I did not make any assumptions, I was just making general observation
that if pressure data is available it is useful not only for drawing
applications.

But
that is not true. The value is not pressure and it is unreliable.

So what is this data then?

Thanks.

-- 
Dmitry