Re: [PATCH v3] Input: synaptics - handle out of bounds values from the hardware

[Seth Forshee <seth.forshee@canonical.com>]

Ping. Any objections to this version?

Thanks,
Seth

On Fri, Jun 29, 2012 at 01:22:18PM -0500, Seth Forshee wrote:
> The touchpad on the Acer Aspire One D250 will report out of range values
> in the extreme lower portion of the touchpad. These appear as abrupt
> changes in the values reported by the hardware from very low values to
> very high values, which can cause unexpected vertical jumps in the
> position of the mouse pointer.
> 
> What seems to be happening is that the value is wrapping to a two's
> compliment negative value of higher resolution than the 13-bit value
> reported by the hardware, with the high-order bits being truncated. The
> safest way to deal with this is to clamp any out of bounds values to the
> minimum or maximum value for the axis.
> 
> Distinguishing between positive and negative is problematic, since we
> lack definitive sign information in the value reported by the hardware.
> The approach taken here is to split the difference between the maximum
> legitimate value for the axis and the maximum possible value that the
> hardware can report, treating values greater than this number as
> negative and all other values as positive. This can be tweaked later if
> hardware is found that operates outside of these parameters.
> 
> BugLink: http://bugs.launchpad.net/bugs/1001251
> Cc: stable@vger.kernel.org
> Cc: Daniel Kurtz <djkurtz@chromium.org>
> Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
> ---
>  drivers/input/mouse/synaptics.c |   27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
> 
> diff --git a/drivers/input/mouse/synaptics.c b/drivers/input/mouse/synaptics.c
> index c6d9869..698f1b8 100644
> --- a/drivers/input/mouse/synaptics.c
> +++ b/drivers/input/mouse/synaptics.c
> @@ -40,6 +40,10 @@
>   * Note that newer firmware allows querying device for maximum useable
>   * coordinates.
>   */
> +#define XMIN 0
> +#define XMAX 6143
> +#define YMIN 0
> +#define YMAX 6143
>  #define XMIN_NOMINAL 1472
>  #define XMAX_NOMINAL 5472
>  #define YMIN_NOMINAL 1408
> @@ -555,6 +559,29 @@ static int synaptics_parse_hw_state(const unsigned char buf[],
>  		hw->right = (buf[0] & 0x02) ? 1 : 0;
>  	}
>  
> +	/*
> +	 * Some hardware is known to wrap negative on the y axis,
> +	 * providing the low-order bits of a higher resolution negative
> +	 * number as a 13-bit unsigned value. No hardware is known to
> +	 * give out-of-bounds values on the high end, but since we're
> +	 * dealing with unspecified behavior we take a conservative
> +	 * approach to handling the out of bounds values.
> +	 *
> +	 * Clamp out of bounds values to the minimum or maximum value
> +	 * for the axis. Use the midpoint between the maximum axis
> +	 * value and maximum possible reported value as the dividing
> +	 * line between positive and negative values.
> +	 */
> +	if (hw->x > ((1 << 13) + XMAX) / 2)
> +		hw->x = XMIN;
> +	else if (hw->x > XMAX)
> +		hw->x = XMAX;
> +
> +	if (hw->y > ((1 << 13) + YMAX) / 2)
> +		hw->y = YMIN;
> +	else if (hw->y > YMAX)
> +		hw->y = YMAX;
> +
>  	return 0;
>  }
>  
> -- 
> 1.7.9.5
> 
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