scanning: add hwmon only systems to scanning.

previously scanning on devices like default Raspberry Pi, would show
things like:

pi@raspberrypi:~ $ iio_info -s
No IIO context found.

However, this is not correct, since it has HWMON devices (which libiio
now understands). So make sure we add this to the scan context. After
the patch is applied, we get things like:

pi@raspberrypi:~/libiio $ ./build/tests/iio_info -s
Available contexts:
        0: (cpu_thermal, rpi_volt on Raspberry Pi 4 Model B Rev 1.1) [local:]

which is correct.

Signed-off-by: Robin Getz <[email protected]>

local.c

@@ -2170,7 +2170,7 @@ static int build_names(void *d, const char *path)
 	char *names = (char *)d;
 	size_t len;
 
-	if (!strstr(path, "iio:device"))
+	if (!strstr(path, "iio:device") && !(WITH_HWMON && strstr(path, "class/hwmon")))
 		return 0;
 
 	iio_snprintf(buf, sizeof(buf), "%s/name", path);
@@ -2195,15 +2195,32 @@ int local_context_scan(struct iio_scan_result *scan_result)
 	bool exists = false;
 	char *desc, *uri, *machine, buf[2 * BUF_SIZE], names[BUF_SIZE];
 	int ret;
+	bool no_iio;
 
 	ret = foreach_in_dir(&exists, "/sys/bus/iio", true, check_device);
-	if (ret < 0 || !exists)
+	no_iio = ret == -ENOENT;
+	if (WITH_HWMON && no_iio)
+		ret = 0; /* Not an error, unless we also have no hwmon devices */
+	if (ret < 0)
 		return 0;
 
 	names[0] = '\0';
-	ret = foreach_in_dir(&names, "/sys/bus/iio/devices", true, build_names);
-	if (ret < 0)
-		return 0;
+	if (!no_iio) {
+		ret = foreach_in_dir(&names, "/sys/bus/iio/devices", true, build_names);
+		if (ret < 0)
+			return 0;
+	}
+
+	if (WITH_HWMON) {
+		ret = foreach_in_dir(&exists, "/sys/class/hwmon", true, check_device);
+		if (ret == -ENOENT && !no_iio)
+			ret = 0; /* IIO devices but no hwmon devices - not an error */
+		if (ret < 0)
+			return 0;
+		ret = foreach_in_dir(&names, "/sys/class/hwmon", true, build_names);
+		if (ret < 0)
+			return 0;
+	}
 
 	machine = cat_file("/sys/firmware/devicetree/base/model");
 	if (!machine)