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
--- a/drivers/hid/hid-input.c
+++ b/drivers/hid/hid-input.c
@@ -149,6 +149,83 @@
}
+/**
+ * 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 @@
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);