ltunify: add Nano receiver c534 (MK270) support

Fix "Unknown protocol 0x0a in devcon notif" errors when trying to list
or pair new devices connected to the Nano receiver with device ID c534.
This receiver is limited to 2 devices only and does not allow unpairing.

Update the hidraw autodetection since the first detected hidraw device
is wrong. Check the interface number, similar to Solaar, this avoids
more complicated HID descriptor parsing.

To confirm whether a device supports the HID++ protocol, either use
`sudo lsusb -v046d:` (without a kernel driver bound to it) or use

    hidrd-convert -o spec /sys/class/hidraw/hidrawX/device/report_descriptor output.txt

to find a Vendor-Specific page.

2 files changed, 62 insertions, 17 deletions

diff --git a/ltunify.c b/ltunify.c
index c82d96f..f5e46f7 100644
--- a/ltunify.c
+++ b/ltunify.c
@@ -32,6 +32,7 @@
 #include <poll.h>
 #include <libgen.h> /* for basename, used during discovery */
 #include <time.h> /* needs -lrt, for clock_gettime as timeout helper */
+#include <stdarg.h>
 
 #ifndef PACKAGE_VERSION
 #	define PACKAGE_VERSION "0.2"
@@ -47,6 +48,7 @@ typedef unsigned char u8;
 
 #define VID_LOGITECH		0x046d
 #define PID_NANO_RECEIVER	0xc52f
+#define PID_NANO_RECEIVER_2	0xc534
 
 #define HEADER_SIZE		3
 #define SHORT_MESSAGE           0x10
@@ -136,6 +138,7 @@ struct msg_dev_name {
 
 struct notif_devcon {
 #define DEVCON_PROT_UNIFYING	0x04
+#define DEVCON_PROT_NANO_LITE	0x0a
 	u8 prot_type; // bits 0..2 is protocol type (4 for unifying), 3..7 is reserved
 #define DEVCON_DEV_TYPE_MASK	0x0f
 // Link status: 0 is established (in range), 1 is not established (out of range)
@@ -413,7 +416,8 @@ bool process_notif_dev_connect(struct hidpp_message *msg, u8 *device_index,
 			"%#04x instead\n", msg->report_id);
 		return false;
 	}
-	if (dcon->prot_type != DEVCON_PROT_UNIFYING) {
+	if (dcon->prot_type != DEVCON_PROT_UNIFYING &&
+	    dcon->prot_type != DEVCON_PROT_NANO_LITE) {
 		fprintf(stderr, "Unknown protocol %#04x in devcon notif\n",
 			dcon->prot_type);
 		return false;
@@ -1138,6 +1142,21 @@ static int validate_args(int argc, char **argv, char ***argsp, char **hidraw_pat
 	return args_count;
 }
 
+#ifdef __GNUC__
+static FILE *fopen_format(const char *format, ...)
+__attribute__((format(printf, 1, 2)));
+#endif
+
+static FILE *fopen_format(const char *format, ...) {
+	char buf[1024];
+	va_list ap;
+
+	va_start(ap, format);
+	vsnprintf(buf, sizeof buf, format, ap);
+	va_end(ap);
+	return fopen(buf, "r");
+}
+
 #define RECEIVER_NAME "logitech-djreceiver"
 int open_hidraw(void) {
 	int fd = -1;
@@ -1152,6 +1171,8 @@ int open_hidraw(void) {
 			char *name = matches.gl_pathv[i];
 			const char *last_comp;
 			char *dev_name;
+			FILE *fp;
+			uint32_t vid = 0, pid = 0;
 
 			r = readlink(name, buf, (sizeof buf) - 1);
 			if (r < 0) {
@@ -1166,25 +1187,46 @@ int open_hidraw(void) {
 			dev_name = name + sizeof "/sys/class/hidraw";
 			*(strchr(dev_name, '/')) = 0;
 
+			// Assume that the first match is the receiver. Devices bound to the
+			// same receiver may have the same modalias.
+			if ((fp = fopen_format("/sys/class/hidraw/%s/device/modalias", dev_name))) {
+				int m = fscanf(fp, "hid:b%*04Xg%*04Xv%08Xp%08X", &vid, &pid);
+				if (m != 2) {
+					pid = 0;
+				}
+				fclose(fp);
+			}
+			if (vid != VID_LOGITECH) {
+				continue;
+			}
+
 			if (!strcmp(last_comp, RECEIVER_NAME)) {
-				/* Logitech receiver c52b and c532 - pass */
-			} else if (!strcmp(last_comp, "hid-generic")) {
-				/* need to test for older nano receiver c52f */
-				FILE *fp;
-				uint32_t vid = 0, pid = 0;
-
-				// Assume that the first match is the receiver. Devices bound to the
-				// same receiver may have the same modalias.
-				snprintf(buf, sizeof buf, "/sys/class/hidraw/%s/device/modalias", dev_name);
-				if ((fp = fopen(buf, "r"))) {
-					int m = fscanf(fp, "hid:b%*04Xg%*04Xv%08Xp%08X", &vid, &pid);
-					if (m != 2) {
-						pid = 0;
+				/* Logitech receiver c52b and c532 - pass.
+				 *
+				 * Logitech Nano receiver c534 however has
+				 * multiple hidraw devices, but the first one is
+				 * only used for keyboard events and should be
+				 * ignored. The second one is for the mouse, and
+				 * that interface has a vendor-specific HID page
+				 * for HID++.
+				 * Parsing .../device/report_descriptor is much
+				 * more complicated, so stick with knowledge
+				 * about device-specific interfaces for now.
+				 */
+				if (pid == PID_NANO_RECEIVER_2) {
+					int iface = -1;
+					if ((fp = fopen_format("/sys/class/hidraw/%s/device/../bInterfaceNumber", dev_name))) {
+						fscanf(fp, "%02x", &iface);
+						fclose(fp);
+					}
+					if (iface == 0) {
+						/* Skip first interface. */
+						continue;
 					}
-					fclose(fp);
 				}
-
-				if (vid != VID_LOGITECH || pid != PID_NANO_RECEIVER) {
+			} else if (!strcmp(last_comp, "hid-generic")) {
+				/* need to test for older nano receiver c52f */
+				if (pid != PID_NANO_RECEIVER) {
 					continue;
 				}
 			} else { /* unknown driver */
diff --git a/udev/42-logitech-unify-permissions.rules b/udev/42-logitech-unify-permissions.rules
index e315fb3..c651410 100644
--- a/udev/42-logitech-unify-permissions.rules
+++ b/udev/42-logitech-unify-permissions.rules
@@ -12,6 +12,9 @@ SUBSYSTEM=="hidraw", ATTRS{idVendor}=="046d", ATTRS{idProduct}=="c532", GOTO="un
 # "Unifying Ready" Nano receiver
 SUBSYSTEM=="hidraw", ATTRS{idVendor}=="046d", ATTRS{idProduct}=="c52f", GOTO="unify_dev"
 
+# Nano receiver for devices such as the MK270 mouse and keyboard combo
+SUBSYSTEM=="hidraw", ATTRS{idVendor}=="046d", ATTRS{idProduct}=="c534", GOTO="unify_dev"
+
 GOTO="not_unify_recv"
 
 LABEL="unify_dev"