Date:	Tue, 23 Mar 2010 18:17:45 -0700
From:	Christopher Heiny <cheiny@...aptics.com>
To:	Arve Hjønnevåg <arve@...roid.com>
CC:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Jean Delvare <khali@...ux-fr.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux Input <linux-input@...r.kernel.org>,
	Allie Xiong <axiong@...aptics.com>,
	William Manson <WManson@...aptics.com>
Subject: Re: [RFC PATCH 0/1] input/touchscreen: Synaptics Touchscreen Driver

On 03/23/2010 03:35 PM, Arve Hjønnevåg wrote:
> 2010/3/23 Christopher Heiny<cheiny@...aptics.com>:
>> On 03/22/2010 08:04 PM, Arve Hjønnevåg wrote:
>>>
>>> On Mon, Mar 22, 2010 at 7:07 PM, Christopher Heiny<cheiny@...aptics.com>
>>>   wrote:
>>> ...
>>>>
>>>> There are two existing drivers for similar Synaptics devices in the
>>>> current kernel tree (excluding the PS/2 touchpad driver).  These are:
>>>>
>>>> ./linux-2.6/drivers/input/mouse/synaptics_i2c.c
>>>>       A driver for the Exeda 15mm touchpad, written by Mike Rapoport
>>>>       <mike@...pulab.co.il>   and Igor Grinberg<grinberg@...pulab.co.il>
>>>>
>>>> ./linux-2.6/drivers/staging/dream/synaptics_i2c_rmi.c
>>>>       A driver for the HTC Dream ClearPad, written by Arve Hjønnevåg
>>>>       <arve@...roid.com>
>>>>
>>>> We have not extended these drivers for a couple of reasons.  First, the
>>>> two drivers are specific to particular Synaptics products, and it is our
>>>> desire to produce a general solution that takes advantage of the 'self
>>>> describing' features of products that use the RMI protocol.
>>>>
>>>
>>> Do you plan to add platform data to align the reported touchscreen
>>> data with the screen behind it, or do the new hardware allow the the
>>> firmware handle this? In the past we even needed separate parameters
>>> for different firmware versions (seen in
>>> drivers/staging/dream/synaptics_i2c_rmi.h).
>>
>> Hi Arve,
>>
>> RMI4 touchscreens allow adjustment of the reported coordinate range (see the
>> F11_2D_Ctrl6..9 registers, page 48 of the current version of the spec at
>> http://www.synaptics.com/developers/manuals).  Using this feature, the
>> device can be configured to report the same number of positions on each axis
>> as there are pixels on the display.
>>
>
> This does not help aligning the touchscreen values with the screen
> behind it. It just moves the linear scaling from userspace (which can
> use fixed or floating point values to preserve subpixel precision) to
> the firmware.

Hi Arve,

It sounds like your concern is for cases when the origin of the 
touchscreen coordinates does not correspond to a corner of the pixel 
area.  Is that correct?

In any case, it's a perfectly valid issue - not all manufacturers take 
care to map the touchscreen to the display screen that way (though most 
do).  Adding a translation control to the driver would be easy - we'll 
put it on the todo list.

>
>> We plan to make these settings accessible via sysfs, so that it can be
>> dynamically tweaked if the user changes the display resolution (not likely
>> on a phone, probable on a tablet/slate/ereader type device). Assuming there
>> are no significant issues with our current patch, we plan to include that in
>> the next one.  We're holding off that implementation because we're still
>> finding our feet on the submission process, and wanted to keep the initial
>> submits small so changes would be more manageable.
>
> You could also post a patch series instead of one patch.

It's more the other direction - we were concerned (validly, it turned 
out) that some extensive changes might be required as a result of 
feedback on the initial submissions, and wanted to keep the codebase 
we'd have to refactor small.

As the codebase grows, we'll switch to using patch series.  Probably 
with the next submission or (more likely) the one after that.

>> Coordinate rotation/reflection settings will be handled at the driver level,
>> again via sysfs.
>>
> Do you also have a plan to let the userspace know that touchscreen
> coordinate x1,y1 correspond to screen coordinate 0,0 and x2,y2
> correspond to screen coordinate xmax,ymax? The android driver sets
> absmin/max to the values reported when touching the display edges (not
> the actual min and max that the touchscreen can report), but other
> solutions are also possible.

We are not planning on that, since it would require the driver to know 
the orientation (standard? rot 90? rot -90? rot 180?) and resolution of 
the display and track whenever that changes.  It is better to handle 
that information at a higher level, which can then tell the touchscreen 
driver the desired resolution/rotation/etc settings.

>> These features should be independent of the touchscreen firmware level.
>
> In the past they have depended on the firmware version for two
> reasons. On one product, firmware changes to improve the edges of the
> screen completely changed the relationship between values reported and
> the physical touch location.

Good point.

> On another product, the physical size of
> the sensor changed, and the firmware version was used to detect this.
> If all RMI4 based product allow field updates of the firmware the
> first case it less important, but we still need to cover the second
> case.

Hmmmm.  I can see a lot of other cases where it might be desirable to 
know the size of the touchscreen in a platform independent manner. 
Certainly the firmware version is not a reliable way to do this going 
forward.  I will contact the spec maintainer and see if we can have the 
device report the relative information in a query.

				Thanks,
					Chris
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