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Input: synaptics - handle out of bounds values from the hardware
commit c039450 upstream. 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. This patch adds handling for these values by converting them to the appropriate negative values. The only tricky part about this is deciding when to treat a number as negative. It stands to reason that if out of range values can be reported on the low end then it could also happen on the high end, so not all out of range values should be treated as negative. 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 Signed-off-by: Seth Forshee <firstname.lastname@example.org> Reviewed-by: Daniel Kurtz <email@example.com> Signed-off-by: Dmitry Torokhov <firstname.lastname@example.org> [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings <email@example.com>
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