diff --git a/ubb-patgen/ubb-patgen.c b/ubb-patgen/ubb-patgen.c
index 58a559b..241ce4e 100644
--- a/ubb-patgen/ubb-patgen.c
+++ b/ubb-patgen/ubb-patgen.c
@@ -489,10 +489,11 @@ static void usage(const char *name)
 "usage: %s\n"
 "       %s [-q] -f freq_hz\n"
 "       %s [-q] [-f freq_hz] -c [active_s]\n"
-"       %s [-q] [-f freq_hz] [-C] [-p] file|pattern\n\n"
+"       %s [-q] [-f freq_hz] [-C] [-m mask] [-p] file|pattern\n\n"
 "  -c          output bus clock on CLK without sending a pattern\n"
 "  -C          temporarily output bus clock on CLK (for debugging)\n"
 "  -f freq_hz  set bus clock to the specified frequency (default: 1 MHz)\n"
+"  -m mask     use only the DATx lines specified in the mask (default: 0xf)\n"
 "  -p          force interpretation of argument as pattern (and not file)\n"
 "  -q          quiet. Don't pretty-print frequencies; don't report clock\n"
 "              differences.\n\n"
@@ -520,10 +521,12 @@ int main(int argc, char **argv)
 	double active_s = 0;
 	struct timespec active_ns;
 	int keep_clk = 1;
+	uint8_t mask = 0xf;
 	char *end;
 	int c;
+	unsigned long tmp;
 
-	while ((c = getopt(argc, argv, "cCf:pq")) != EOF)
+	while ((c = getopt(argc, argv, "cCf:m:pq")) != EOF)
 		switch (c) {
 		case 'f':
 			if (!frequency(optarg, &bus_hz, &bus_rel))
@@ -535,6 +538,16 @@ int main(int argc, char **argv)
 		case 'C':
 			clkout = 1;
 			break;
+		case 'm':
+			tmp = strtoul(optarg, &end, 0);
+			if (*end)
+				usage(*argv);
+			if (tmp & ~0xfUL) {
+				fprintf(stderr, "mask is too large\n");
+				exit(1);
+			}
+			mask = tmp;
+			break;
 		case 'p':
 			force_pattern = 1;
 			break;
@@ -616,15 +629,14 @@ int main(int argc, char **argv)
 	mmcclk_start(&clk);
 
 	if (pattern)
-		dma_pattern(&clk, pattern,
-		    UBB_DAT0 | UBB_DAT1 | UBB_DAT2 | UBB_DAT3);
+		dma_pattern(&clk, pattern, mask << 10);
 
 	if (active_s)
 		if (nanosleep(&active_ns, NULL))
 			perror("nanosleep");
 	if (pattern) {
 		mmcclk_stop();
-		ubb_close(UBB_DAT0 | UBB_DAT1 | UBB_DAT2 | UBB_DAT3);
+		ubb_close(mask << 10);
 	} else if (keep_clk) {
 		ubb_close(UBB_CLK);
 	} else {