Index: src/sys/dev/ic/pcf8584.c
===================================================================
RCS file: /cvsroot/src/sys/dev/ic/pcf8584.c,v
retrieving revision 1.11
diff -u -r1.11 pcf8584.c
--- src/sys/dev/ic/pcf8584.c	20 Jan 2014 22:02:32 -0000	1.11
+++ src/sys/dev/ic/pcf8584.c	15 Dec 2015 07:57:05 -0000
@@ -175,14 +175,28 @@
 	if (sc->sc_master)
 		pcfiic_choose_bus(sc, addr >> 7);
 
-	if (pcfiic_xmit(sc, addr & 0x7f, cmdbuf, cmdlen) != 0)
-		return (1);
-
-	if (len > 0) {
-		if (I2C_OP_WRITE_P(op))
-			ret = pcfiic_xmit(sc, addr & 0x7f, buf, len);
-		else
-			ret = pcfiic_recv(sc, addr & 0x7f, buf, len);
+	/*
+	 * If we are writing, write address, cmdbuf, buf.
+	 * If we are reading, write address, cmdbuf, then read address, buf.
+	 */
+	if (I2C_OP_WRITE_P(op)) {
+		if (len > 0) {
+			uint8_t *tmp;
+
+			tmp = malloc(cmdlen + len, M_DEVBUF,
+			   flags & I2C_F_POLL ? M_NOWAIT : M_WAITOK);
+			if (tmp == NULL)
+				return (1);
+			memcpy(tmp, cmdbuf, cmdlen);
+			memcpy(tmp + cmdlen, buf, len);
+			ret = pcfiic_xmit(sc, addr & 0x7f, tmp, cmdlen + len);
+			free(tmp, M_DEVBUF);
+		} else
+			ret = pcfiic_xmit(sc, addr & 0x7f, cmdbuf, cmdlen);
+	} else {
+		if (pcfiic_xmit(sc, addr & 0x7f, cmdbuf, cmdlen) != 0)
+			return (1);
+		ret = pcfiic_recv(sc, addr & 0x7f, buf, len);
 	}
 	return (ret);
 }