Implement and document "-S noauto" to inhibit autoscanning without specifying a serial device

README

@@ -205,10 +205,11 @@ FPGA mining boards(BitForce, Icarus) only options:
 --scan-serial|-S <arg> Serial port to probe for FPGA mining device
 
      By default, cgminer will scan for autodetected FPGAs unless at least one
-     -S is specified. If you specify -S and still want cgminer to scan, you
+     -S is specified for that driver. If you specify -S and still want cgminer
-     must also use "-S auto". Note that presently, autodetection only works
+     to scan, you must also use "-S auto". If you want to prevent cgminer from
-     on Linux, and might only detect one device depending on the version of
+     scanning without specifying a device, you can use "-S noauto". Note that
-     udev being used.
+     presently, autodetection only works on Linux, and might only detect one
+     device depending on the version of udev being used.
 
      On linux <arg> is usually of the format /dev/ttyUSBn
      On windows <arg> is usually of the format COMn

driver-bitforce.c

@@ -216,6 +216,9 @@ static void bitforce_detect()
 			s += 9;
 		if (!strcmp(s, "auto"))
 			autoscan = true;
+		else
+		if (!strcmp(s, "noauto"))
+			found = true;
 		else if (bitforce_detect_one(s)) {
 			string_elist_del(iter);
 			found = true;

driver-icarus.c

@@ -246,7 +246,7 @@ static void icarus_detect()
 		s = iter->string;
 		if (!strncmp("icarus:", iter->string, 7))
 			s += 7;
-		if (!strcmp(s, "auto"))
+		if (!strcmp(s, "auto") || !strcmp(s, "noauto"))
 			continue;
 		if (icarus_detect_one(s))
 			string_elist_del(iter);