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>
diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
index f4109fd..f5004e2 100644
--- a/drivers/hid/hid-core.c
+++ b/drivers/hid/hid-core.c
@@ -315,6 +315,7 @@
static int hid_parser_global(struct hid_parser *parser, struct hid_item *item)
{
+ __u32 raw_value;
switch (item->tag) {
case HID_GLOBAL_ITEM_TAG_PUSH:
@@ -365,7 +366,14 @@
return 0;
case HID_GLOBAL_ITEM_TAG_UNIT_EXPONENT:
- parser->global.unit_exponent = item_sdata(item);
+ /* Units exponent negative numbers are given through a
+ * two's complement.
+ * See "6.2.2.7 Global Items" for more information. */
+ raw_value = item_udata(item);
+ if (!(raw_value & 0xfffffff0))
+ parser->global.unit_exponent = hid_snto32(raw_value, 4);
+ else
+ parser->global.unit_exponent = raw_value;
return 0;
case HID_GLOBAL_ITEM_TAG_UNIT:
@@ -865,6 +873,12 @@
return value & (1 << (n - 1)) ? value | (-1 << n) : value;
}
+s32 hid_snto32(__u32 value, unsigned n)
+{
+ return snto32(value, n);
+}
+EXPORT_SYMBOL_GPL(hid_snto32);
+
/*
* Convert a signed 32-bit integer to a signed n-bit integer.
*/