HID: add absolute axis resolution calculation

Add absolute axis resolution calculation to the core HID layer, according to HID
specification v1.11 6.2.2.7 Global Items. Only exponent 1 length units for
X/Y/Z/RX/RY/RZ axis are supported for now.

Signed-off-by: Nikolai Kondrashov <spbnick@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

diff --git a/drivers/hid/hid-input.c b/drivers/hid/hid-input.c
index 6c03dcc..8e733b6 100644 (file)
--- a/drivers/hid/hid-input.c
+++ b/drivers/hid/hid-input.c
@@ -149,6 +149,83 @@ static int hidinput_setkeycode(struct input_dev *dev,
 }
 
 
+/**
+ * hidinput_calc_abs_res - calculate an absolute axis resolution
+ * @field: the HID report field to calculate resolution for
+ * @code: axis code
+ *
+ * The formula is:
+ *                         (logical_maximum - logical_minimum)
+ * resolution = ----------------------------------------------------------
+ *              (physical_maximum - physical_minimum) * 10 ^ unit_exponent
+ *
+ * as seen in the HID specification v1.11 6.2.2.7 Global Items.
+ *
+ * Only exponent 1 length units are processed. Centimeters are converted to
+ * inches. Degrees are converted to radians.
+ */
+static __s32 hidinput_calc_abs_res(const struct hid_field *field, __u16 code)
+{
+       __s32 unit_exponent = field->unit_exponent;
+       __s32 logical_extents = field->logical_maximum -
+                                       field->logical_minimum;
+       __s32 physical_extents = field->physical_maximum -
+                                       field->physical_minimum;
+       __s32 prev;
+
+       /* Check if the extents are sane */
+       if (logical_extents <= 0 || physical_extents <= 0)
+               return 0;
+
+       /*
+        * Verify and convert units.
+        * See HID specification v1.11 6.2.2.7 Global Items for unit decoding
+        */
+       if (code == ABS_X || code == ABS_Y || code == ABS_Z) {
+               if (field->unit == 0x11) {              /* If centimeters */
+                       /* Convert to inches */
+                       prev = logical_extents;
+                       logical_extents *= 254;
+                       if (logical_extents < prev)
+                               return 0;
+                       unit_exponent += 2;
+               } else if (field->unit != 0x13) {       /* If not inches */
+                       return 0;
+               }
+       } else if (code == ABS_RX || code == ABS_RY || code == ABS_RZ) {
+               if (field->unit == 0x14) {              /* If degrees */
+                       /* Convert to radians */
+                       prev = logical_extents;
+                       logical_extents *= 573;
+                       if (logical_extents < prev)
+                               return 0;
+                       unit_exponent += 1;
+               } else if (field->unit != 0x12) {       /* If not radians */
+                       return 0;
+               }
+       } else {
+               return 0;
+       }
+
+       /* Apply negative unit exponent */
+       for (; unit_exponent < 0; unit_exponent++) {
+               prev = logical_extents;
+               logical_extents *= 10;
+               if (logical_extents < prev)
+                       return 0;
+       }
+       /* Apply positive unit exponent */
+       for (; unit_exponent > 0; unit_exponent--) {
+               prev = physical_extents;
+               physical_extents *= 10;
+               if (physical_extents < prev)
+                       return 0;
+       }
+
+       /* Calculate resolution */
+       return logical_extents / physical_extents;
+}
+
 static void hidinput_configure_usage(struct hid_input *hidinput, struct hid_field *field,
                                     struct hid_usage *usage)
 {
@@ -537,6 +614,9 @@ mapped:
                        input_set_abs_params(input, usage->code, a, b, (b - a) >> 8, (b - a) >> 4);
                else    input_set_abs_params(input, usage->code, a, b, 0, 0);
 
+               input_abs_set_res(input, usage->code,
+                                 hidinput_calc_abs_res(field, usage->code));
+
                /* use a larger default input buffer for MT devices */
                if (usage->code == ABS_MT_POSITION_X && input->hint_events_per_packet == 0)
                        input_set_events_per_packet(input, 60);