linux-kernel - Re: [RFC ebeam PATCH 2/2] input: misc: New USB eBeam input driver

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Message-ID: <55AE389F.9060409@laposte.net>
Date:	Tue, 21 Jul 2015 14:18:39 +0200
From:	Yann Cantin <yann.cantin@...oste.net>
To:	Greg KH <gregkh@...uxfoundation.org>
CC:	linux-input@...r.kernel.org, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	dmitry.torokhov@...il.com, jkosina@...e.cz
Subject: Re: [RFC ebeam PATCH 2/2] input: misc: New USB eBeam input driver

Hi,

Le 20/07/2015 23:59, Greg KH a écrit :
> On Mon, Jul 20, 2015 at 11:03:19PM +0200, Yann Cantin wrote:
>> diff --git a/Documentation/ABI/testing/sysfs-driver-ebeam b/Documentation/ABI/testing/sysfs-driver-ebeam
>> +++ b/Documentation/ABI/testing/sysfs-driver-ebeam
>> @@ -0,0 +1,53 @@
>> +What:		/sys/class/input/inputXX/device/min_x
>> +		/sys/class/input/inputXX/device/min_y
>> +		/sys/class/input/inputXX/device/max_x
>> +		/sys/class/input/inputXX/device/max_y
>> +What:		/sys/class/input/inputXX/device/h[1..9]
>> +What:		/sys/class/input/inputXX/device/calibrated
>
>
> What tool(s) use these sysfs files?  Don't we already have "normal"
> events for these types of things such that we don't have to make up new
> sysfs files for these?

The ebeam_calibrator tool is there : http://ebeam.tuxfamily.org.

I agree this can be a problem : this driver is totally useless without a
userspace dedicated calibration tool.

By nature these device's coordinate system can't be mapped to screen via
trivial transformations, such as scaling, flipping and rotating, hence the
special calibration and mapping procedures. I choose to use an homography
transformation as it is more robust and faster than linear interpolation
in this case. And anyway, it requires 9 calibration data and xy range
parameters.

I haven't found any existing tools performing that : xinput_calibrator
(witch ebeam_calibrator is based on) and other touchscreen calibration
tools can't do much more than trivial transformations.


>> +static DEVICE_ATTR(MM, S_IRUSR | S_IRGRP | S_IWUSR | S_IWGRP,		       \
>> +		   ebeam_##MM##_get,					       \
>> +		   ebeam_##MM##_set)
>
> DEVICE_ATTR_RW()?

Ok, will do.


>> +	/* sysfs setup */
>> +	err = sysfs_create_group(&intf->dev.kobj, &ebeam_attr_group);
>
> Ick, you just added the sysfs files to the USB device, not your input
> device, are you sure you tested this?

Yes, "run fine since 3.3.6, both x86_32 and 64.".

thanks,

-- 
Yann Cantin
A4FEB47F
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