Re: [PATCH 3/3] Add support for Cintiq 27QHD and 27QHD touch

[Peter Hutterer <peter.hutterer@who-t.net>]

On Tue, Jan 27, 2015 at 01:30:03PM -0800, Ping Cheng wrote:
> These devices have accelerometers. To report accelerometer coordinates,
> a new property, INPUT_PROP_ACCELEROMETER, is added.
> 
> Signed-off-by: Ping Cheng <pingc@wacom.com>
> ---

[...]

> diff --git a/include/uapi/linux/input.h b/include/uapi/linux/input.h
> index a1d7e93..b0a8130 100644
> --- a/include/uapi/linux/input.h
> +++ b/include/uapi/linux/input.h
> @@ -166,6 +166,7 @@ struct input_keymap_entry {
>  #define INPUT_PROP_SEMI_MT		0x03	/* touch rectangle only */
>  #define INPUT_PROP_TOPBUTTONPAD		0x04	/* softbuttons at top of pad */
>  #define INPUT_PROP_POINTING_STICK	0x05	/* is a pointing stick */
> +#define INPUT_PROP_ACCELEROMETER	0x06	/* has accelerometer */
>  
>  #define INPUT_PROP_MAX			0x1f
>  #define INPUT_PROP_CNT			(INPUT_PROP_MAX + 1)
> -- 
> 1.9.1

I just ran into this and have a few questions:
what is the intended meaning of INPUT_PROP_ACCELEROMETER? For all the other
props it's obvious what they mean but here there it is a bit more ambiguous.

Specifically, if a device is tagged as accelerometer, which axes have
accelerometer data? just ABS_X/Y/Z and/or REL_X/Y/Z? or do we have a
requirement that _all_ axes on that device must reflect accelerometer data
(because realistically ABS_RX could be an accelerometer while x and y is a
normal axis). Or is it up for grabs and you need other information
to know which axes exported are accelerometers?

I know what it does on the 27QHD, but this is a generic tag so we need to
define this for all devices.

Cheers,
   Peter