diff --git a/usr.sbin/spi/spi.8 b/usr.sbin/spi/spi.8
--- a/usr.sbin/spi/spi.8
+++ b/usr.sbin/spi/spi.8
@@ -38,6 +38,7 @@
 .Op Fl d Cm r Ns | Ns Cm w Ns | Ns Cm rw
 .Op Fl f Ar device
 .Op Fl m Ar mode
+.Op Fl S
 .Op Fl s Ar max-speed
 .Nm
 .Op Fl i
@@ -145,6 +146,12 @@
 SPI mode, 0 through 3.
 This defines the clock phase and timing with respect to reading and writing
 data, as per the SPI specification.
+.It Fl S
+Constantly stream from
+.Xr stdin 3
+to the
+.Nm
+bus.
 .It Fl s Ar speed
 Specify the maximum speed, in Hz, for the SPI clock.
 The bus will operate at its highest available speed which does not
diff --git a/usr.sbin/spi/spi.c b/usr.sbin/spi/spi.c
--- a/usr.sbin/spi/spi.c
+++ b/usr.sbin/spi/spi.c
@@ -129,7 +129,7 @@
 	fputs(" - communicate on SPI bus with slave devices\n"
 	      "Usage:\n"
 	      "        spi [-f device] [-d r|w|rw] [-m mode] [-s max-speed] [-c count]\n"
-	      "            [-C \"command bytes\"] [-A] [-b] [-L] [-v]\n"
+	      "            [-C \"command bytes\"] [-A] [-b] [-L] [-S] [-v]\n"
 	      "        spi -i [-f device] [-v]\n"
 	      "        spi -h\n"
 	      " where\n"
@@ -145,6 +145,7 @@
 	      "        -i query information about the device\n"
 	      "        -A uses ASCII for input/output as 2-digit hex values\n"
 	      "        -b Override output format as binary (only valid with '-A')\n"
+	      "        -S constantly stream from stdin to bus\n"
 	      "        -v verbose output\n"
 	      "        -h prints this message\n"
 	      "\n"
@@ -158,11 +159,12 @@
 main(int argc, char *argv[], char *envp[] __unused)
 {
 	struct spi_options opt;
-	int err, ch, hdev, finfo, fdir;
+	int err, ch, hdev, finfo, stream, fdir;
 	char *pstr;
 	char dev_name[PATH_MAX * 2 + 5];
 
 	finfo = 0;
+	stream = 0;
 	fdir = DIR_NONE;
 
 	hdev = -1;
@@ -180,7 +182,7 @@
 	opt.ncmd = 0;
 	opt.pcmd = NULL;
 
-	while (!err && (ch = getopt(argc, argv, "f:d:m:s:c:C:AbLvih")) != -1) {
+	while (!err && (ch = getopt(argc, argv, "f:d:m:s:c:C:AbLviSh")) != -1) {
 		switch (ch) {
 		case 'd':
 			if (optarg[0] == 'r') {
@@ -275,6 +277,10 @@
 			finfo = 1;
 			break;
 
+		case 'S':
+			stream = 1;
+			break;
+
 		default:
 			err = 1;
 			/* FALLTHROUGH */
@@ -358,14 +364,29 @@
 
 	/* do data transfer */
 
-	if (fdir == DIR_READ) {
-		err = perform_read(hdev, &opt);
-	}
-	else if (fdir == DIR_WRITE) {
-		err = perform_write(hdev, &opt);
+	if (stream) {
+		while (!err && !feof(stdin)) {
+			if (fdir == DIR_READ) {
+				err = perform_read(hdev, &opt);
+			}
+			else if (fdir == DIR_WRITE) {
+				err = perform_write(hdev, &opt);
+			}
+			else if (fdir == DIR_READWRITE) {
+				err = perform_readwrite(hdev, &opt);
+			}
+		}
 	}
-	else if (fdir == DIR_READWRITE) {
-		err = perform_readwrite(hdev, &opt);
+	else {
+		if (fdir == DIR_READ) {
+			err = perform_read(hdev, &opt);
+		}
+		else if (fdir == DIR_WRITE) {
+			err = perform_write(hdev, &opt);
+		}
+		else if (fdir == DIR_READWRITE) {
+			err = perform_readwrite(hdev, &opt);
+		}
 	}
 
 the_end: