Index: sys/dev/smbus/smb.h
===================================================================
--- sys/dev/smbus/smb.h
+++ sys/dev/smbus/smb.h
@@ -63,11 +63,13 @@
 #define SMB_RECVB	_IOWR('i', 4, struct smbcmd)
 #define SMB_WRITEB	_IOW('i', 5, struct smbcmd)
 #define SMB_WRITEW	_IOW('i', 6, struct smbcmd)
-#define SMB_READB	_IOW('i', 7, struct smbcmd)
-#define SMB_READW	_IOW('i', 8, struct smbcmd)
-#define SMB_PCALL	_IOW('i', 9, struct smbcmd)
+#define SMB_OLD_READB	_IOW('i', 7, struct smbcmd)
+#define SMB_READB	_IOWR('i', 7, struct smbcmd)
+#define SMB_OLD_READW	_IOW('i', 8, struct smbcmd)
+#define SMB_READW	_IOWR('i', 8, struct smbcmd)
+#define SMB_OLD_PCALL	_IOW('i', 9, struct smbcmd)
+#define SMB_PCALL	_IOWR('i', 9, struct smbcmd)
 #define SMB_BWRITE	_IOW('i', 10, struct smbcmd)
-#define SMB_OLD_BREAD	_IOW('i', 11, struct smbcmd)
 #define SMB_BREAD	_IOWR('i', 11, struct smbcmd)
 #define SMB_OLD_TRANS	_IOWR('i', 12, struct smbcmd)
 
Index: sys/dev/smbus/smb.c
===================================================================
--- sys/dev/smbus/smb.c
+++ sys/dev/smbus/smb.c
@@ -224,7 +224,9 @@
 						s->cmd, s->wdata.word));
 		break;
 
+	case SMB_OLD_READB:
 	case SMB_READB:
+		/* NB: for SMB_OLD_READB the read data goes to rbuf only. */
 		error = smbus_error(smbus_readb(parent, s->slave, s->cmd,
 		    &s->rdata.byte));
 		if (error)
@@ -235,7 +237,9 @@
 		}
 		break;
 
+	case SMB_OLD_READW:
 	case SMB_READW:
+		/* NB: for SMB_OLD_READW the read data goes to rbuf only. */
 		error = smbus_error(smbus_readw(parent, s->slave, s->cmd,
 		    &s->rdata.word));
 		if (error)
@@ -248,7 +252,9 @@
 		}
 		break;
 
+	case SMB_OLD_PCALL:
 	case SMB_PCALL:
+		/* NB: for SMB_OLD_PCALL the read data goes to rbuf only. */
 		error = smbus_error(smbus_pcall(parent, s->slave, s->cmd,
 		    s->wdata.word, &s->rdata.word));
 		if (error)