HID: logitech-hidpp: use RAP instead of FAP to get the protocol version

According to the logitech_hidpp_2.0_specification_draft_2012-06-04.pdf doc:
https://lekensteyn.nl/files/logitech/logitech_hidpp_2.0_specification_draft_2012-06-04.pdf

We should use a register-access-protocol request using the short input /
output report ids. This is necessary because 27MHz HID++ receivers have
a max-packetsize on their HIP++ endpoint of 8, so they cannot support
long reports. Using a feature-access-protocol request (which is always
long or very-long) with these will cause a timeout error, followed by
the hidpp driver treating the device as not being HID++ capable.

This commit fixes this by switching to using a rap request to get the
protocol version.

Besides being tested with a (046d:c517) 27MHz receiver with various
27MHz keyboards and mice, this has also been tested to not cause
regressions on a non-unifying dual-HID++ nano receiver (046d:c534) with
k270 and m185 HID++-2.0 devices connected and on a unifying/dj receiver
(046d:c52b) with a HID++-2.0 Logitech Rechargeable Touchpad T650.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

drivers/hid/hid-logitech-hidpp.c

@@ -837,13 +837,16 @@ static int hidpp_root_get_feature(struct hidpp_device *hidpp, u16 feature,
 
 static int hidpp_root_get_protocol_version(struct hidpp_device *hidpp)
 {
+	const u8 ping_byte = 0x5a;
+	u8 ping_data[3] = { 0, 0, ping_byte };
 	struct hidpp_report response;
 	int ret;
 
-	ret = hidpp_send_fap_command_sync(hidpp,
+	ret = hidpp_send_rap_command_sync(hidpp,
+			REPORT_ID_HIDPP_SHORT,
 			HIDPP_PAGE_ROOT_IDX,
 			CMD_ROOT_GET_PROTOCOL_VERSION,
-			NULL, 0, &response);
+			ping_data, sizeof(ping_data), &response);
 
 	if (ret == HIDPP_ERROR_INVALID_SUBID) {
 		hidpp->protocol_major = 1;
@@ -863,8 +866,14 @@ static int hidpp_root_get_protocol_version(struct hidpp_device *hidpp)
 	if (ret)
 		return ret;
 
-	hidpp->protocol_major = response.fap.params[0];
-	hidpp->protocol_minor = response.fap.params[1];
+	if (response.rap.params[2] != ping_byte) {
+		hid_err(hidpp->hid_dev, "%s: ping mismatch 0x%02x != 0x%02x\n",
+			__func__, response.rap.params[2], ping_byte);
+		return -EPROTO;
+	}
+
+	hidpp->protocol_major = response.rap.params[0];
+	hidpp->protocol_minor = response.rap.params[1];
 
 print_version:
 	hid_info(hidpp->hid_dev, "HID++ %u.%u device connected.\n",