HID: fix unit exponent parsing

HID spec details special values for the HID field unit exponent.
Basically, the range [0x8..0xf] correspond to [-8..-1], so this is
a standard two's complement on a half-byte.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>
Acked-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

1 files changed, 9 insertions, 4 deletions

diff --git a/drivers/hid/hid-input.c b/drivers/hid/hid-input.c
index 1b0adc3f7803..007a9433bfa7 100644
--- a/drivers/hid/hid-input.c
+++ b/drivers/hid/hid-input.c
@@ -192,7 +192,6 @@ static int hidinput_setkeycode(struct input_dev *dev,
         return -EINVAL;
 }
 
-
 /**
  * hidinput_calc_abs_res - calculate an absolute axis resolution
  * @field: the HID report field to calculate resolution for
@@ -235,17 +234,23 @@ __s32 hidinput_calc_abs_res(const struct hid_field *field, __u16 code)
         case ABS_MT_TOOL_Y:
         case ABS_MT_TOUCH_MAJOR:
         case ABS_MT_TOUCH_MINOR:
-                if (field->unit == 0x11) {              /* If centimeters */
+                if (field->unit & 0xffffff00)           /* Not a length */
+                        return 0;
+                unit_exponent += hid_snto32(field->unit >> 4, 4) - 1;
+                switch (field->unit & 0xf) {
+                case 0x1:                               /* If centimeters */
                         /* Convert to millimeters */
                         unit_exponent += 1;
-                } else if (field->unit == 0x13) {       /* If inches */
+                        break;
+                case 0x3:                               /* If inches */
                         /* Convert to millimeters */
                         prev = physical_extents;
                         physical_extents *= 254;
                         if (physical_extents < prev)
                                 return 0;
                         unit_exponent -= 1;
-                } else {
+                        break;
+                default:
                         return 0;
                 }
                 break;