HID: logitech: Add function to enable HID++ 1.0 "scrolling acceleration"

"Scrolling acceleration" is a bit of a misnomer: it doesn't deal with
acceleration at all. However, that's the name used in Logitech's spec,
so I used it here.
Signed-off-by: Harry Cutts <hcutts@chromium.org>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/hid-logitech-hidpp.c

@@ -400,9 +400,15 @@ static void hidpp_prefix_name(char **name, int name_length)
 #define HIDPP_SET_LONG_REGISTER				0x82
 #define HIDPP_GET_LONG_REGISTER				0x83
 
-#define HIDPP_REG_GENERAL				0x00
-
-static int hidpp10_enable_battery_reporting(struct hidpp_device *hidpp_dev)
+/**
+ * hidpp10_set_register_bit() - Sets a single bit in a HID++ 1.0 register.
+ * @hidpp_dev: the device to set the register on.
+ * @register_address: the address of the register to modify.
+ * @byte: the byte of the register to modify. Should be less than 3.
+ * Return: 0 if successful, otherwise a negative error code.
+ */
+static int hidpp10_set_register_bit(struct hidpp_device *hidpp_dev,
+	u8 register_address, u8 byte, u8 bit)
 {
 	struct hidpp_report response;
 	int ret;
@@ -411,23 +417,38 @@ static int hidpp10_enable_battery_reporting(struct hidpp_device *hidpp_dev)
 	ret = hidpp_send_rap_command_sync(hidpp_dev,
 					  REPORT_ID_HIDPP_SHORT,
 					  HIDPP_GET_REGISTER,
-					HIDPP_REG_GENERAL,
+					  register_address,
 					  NULL, 0, &response);
 	if (ret)
 		return ret;
 
 	memcpy(params, response.rap.params, 3);
 
-	/* Set the battery bit */
-	params[0] |= BIT(4);
+	params[byte] |= BIT(bit);
 
 	return hidpp_send_rap_command_sync(hidpp_dev,
 					   REPORT_ID_HIDPP_SHORT,
 					   HIDPP_SET_REGISTER,
-					HIDPP_REG_GENERAL,
+					   register_address,
 					   params, 3, &response);
 }
 
+
+#define HIDPP_REG_GENERAL				0x00
+
+static int hidpp10_enable_battery_reporting(struct hidpp_device *hidpp_dev)
+{
+	return hidpp10_set_register_bit(hidpp_dev, HIDPP_REG_GENERAL, 0, 4);
+}
+
+#define HIDPP_REG_FEATURES				0x01
+
+/* On HID++ 1.0 devices, high-res scroll was called "scrolling acceleration". */
+static int hidpp10_enable_scrolling_acceleration(struct hidpp_device *hidpp_dev)
+{
+	return hidpp10_set_register_bit(hidpp_dev, HIDPP_REG_FEATURES, 0, 6);
+}
+
 #define HIDPP_REG_BATTERY_STATUS			0x07
 
 static int hidpp10_battery_status_map_level(u8 param)