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>

1 files changed, 80 insertions, 0 deletions

diff --git a/drivers/hid/hid-input.c b/drivers/hid/hid-input.c
index 6c03dcc5760a..8e733b6eae27 100644
--- 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);