diff --git a/sound/firewire/cmp.c b/sound/firewire/cmp.c
index efdbf58..17ad4f2 100644
--- a/sound/firewire/cmp.c
+++ b/sound/firewire/cmp.c
@@ -14,18 +14,20 @@
 #include "iso-resources.h"
 #include "cmp.h"
 
-#define IMPR_SPEED_MASK		0xc0000000
-#define IMPR_SPEED_SHIFT	30
-#define IMPR_XSPEED_MASK	0x00000060
-#define IMPR_XSPEED_SHIFT	5
-#define IMPR_PLUGS_MASK		0x0000001f
-
-#define IPCR_ONLINE		0x80000000
-#define IPCR_BCAST_CONN		0x40000000
-#define IPCR_P2P_CONN_MASK	0x3f000000
-#define IPCR_P2P_CONN_SHIFT	24
-#define IPCR_CHANNEL_MASK	0x003f0000
-#define IPCR_CHANNEL_SHIFT	16
+/* MPR common fields */
+#define MPR_SPEED_MASK		0xc0000000
+#define MPR_SPEED_SHIFT		30
+#define MPR_XSPEED_MASK		0x00000060
+#define MPR_XSPEED_SHIFT	5
+#define MPR_PLUGS_MASK		0x0000001f
+
+/* PCR common fields */
+#define PCR_ONLINE		0x80000000
+#define PCR_BCAST_CONN		0x40000000
+#define PCR_P2P_CONN_MASK	0x3f000000
+#define PCR_P2P_CONN_SHIFT	24
+#define PCR_CHANNEL_MASK	0x003f0000
+#define PCR_CHANNEL_SHIFT	16
 
 enum bus_reset_handling {
 	ABORT_ON_BUS_RESET,
@@ -88,24 +90,24 @@ static int pcr_modify(struct cmp_connection *c,
  * cmp_connection_init - initializes a connection manager
  * @c: the connection manager to initialize
  * @unit: a unit of the target device
- * @ipcr_index: the index of the iPCR on the target device
+ * @pcr_index: the index of the iPCR/oPCR on the target device
  */
 int cmp_connection_init(struct cmp_connection *c,
 			struct fw_unit *unit,
-			unsigned int ipcr_index)
+			unsigned int pcr_index)
 {
-	__be32 impr_be;
-	u32 impr;
+	__be32 mpr_be;
+	u32 mpr;
 	int err;
 
 	err = snd_fw_transaction(unit, TCODE_READ_QUADLET_REQUEST,
 				 CSR_REGISTER_BASE + CSR_IMPR,
-				 &impr_be, 4, 0);
+				 &mpr_be, 4, 0);
 	if (err < 0)
 		return err;
-	impr = be32_to_cpu(impr_be);
+	mpr = be32_to_cpu(mpr_be);
 
-	if (ipcr_index >= (impr & IMPR_PLUGS_MASK))
+	if (pcr_index >= (mpr & MPR_PLUGS_MASK))
 		return -EINVAL;
 
 	err = fw_iso_resources_init(&c->resources, unit);
@@ -115,10 +117,10 @@ int cmp_connection_init(struct cmp_connection *c,
 	c->connected = false;
 	mutex_init(&c->mutex);
 	c->last_pcr_value = cpu_to_be32(0x80000000);
-	c->pcr_index = ipcr_index;
-	c->max_speed = (impr & IMPR_SPEED_MASK) >> IMPR_SPEED_SHIFT;
+	c->pcr_index = pcr_index;
+	c->max_speed = (mpr & MPR_SPEED_MASK) >> MPR_SPEED_SHIFT;
 	if (c->max_speed == SCODE_BETA)
-		c->max_speed += (impr & IMPR_XSPEED_MASK) >> IMPR_XSPEED_SHIFT;
+		c->max_speed += (mpr & MPR_XSPEED_MASK) >> MPR_XSPEED_SHIFT;
 
 	return 0;
 }
@@ -139,23 +141,23 @@ EXPORT_SYMBOL(cmp_connection_destroy);
 
 static __be32 ipcr_set_modify(struct cmp_connection *c, __be32 ipcr)
 {
-	ipcr &= ~cpu_to_be32(IPCR_BCAST_CONN |
-			     IPCR_P2P_CONN_MASK |
-			     IPCR_CHANNEL_MASK);
-	ipcr |= cpu_to_be32(1 << IPCR_P2P_CONN_SHIFT);
-	ipcr |= cpu_to_be32(c->resources.channel << IPCR_CHANNEL_SHIFT);
+	ipcr &= ~cpu_to_be32(PCR_BCAST_CONN |
+			     PCR_P2P_CONN_MASK |
+			     PCR_CHANNEL_MASK);
+	ipcr |= cpu_to_be32(1 << PCR_P2P_CONN_SHIFT);
+	ipcr |= cpu_to_be32(c->resources.channel << PCR_CHANNEL_SHIFT);
 
 	return ipcr;
 }
 
-static int ipcr_set_check(struct cmp_connection *c, __be32 ipcr)
+static int pcr_set_check(struct cmp_connection *c, __be32 pcr)
 {
-	if (ipcr & cpu_to_be32(IPCR_BCAST_CONN |
-			       IPCR_P2P_CONN_MASK)) {
+	if (pcr & cpu_to_be32(PCR_BCAST_CONN |
+			       PCR_P2P_CONN_MASK)) {
 		cmp_error(c, "plug is already in use\n");
 		return -EBUSY;
 	}
-	if (!(ipcr & cpu_to_be32(IPCR_ONLINE))) {
+	if (!(pcr & cpu_to_be32(PCR_ONLINE))) {
 		cmp_error(c, "plug is not on-line\n");
 		return -ECONNREFUSED;
 	}
@@ -170,9 +172,9 @@ static int ipcr_set_check(struct cmp_connection *c, __be32 ipcr)
  *
  * This function establishes a point-to-point connection from the local
  * computer to the target by allocating isochronous resources (channel and
- * bandwidth) and setting the target's input plug control register.  When this
- * function succeeds, the caller is responsible for starting transmitting
- * packets.
+ * bandwidth) and setting the target's input/output plug control register.
+ * When this function succeeds, the caller is responsible for starting
+ * transmitting packets.
  */
 int cmp_connection_establish(struct cmp_connection *c,
 			     unsigned int max_payload_bytes)
@@ -193,7 +195,7 @@ retry_after_bus_reset:
 	if (err < 0)
 		goto err_mutex;
 
-	err = pcr_modify(c, ipcr_set_modify, ipcr_set_check,
+	err = pcr_modify(c, ipcr_set_modify, pcr_set_check,
 			 ABORT_ON_BUS_RESET);
 	if (err == -EAGAIN) {
 		fw_iso_resources_free(&c->resources);
@@ -221,8 +223,8 @@ EXPORT_SYMBOL(cmp_connection_establish);
  * cmp_connection_update - update the connection after a bus reset
  * @c: the connection manager
  *
- * This function must be called from the driver's .update handler to reestablish
- * any connection that might have been active.
+ * This function must be called from the driver's .update handler to
+ * reestablish any connection that might have been active.
  *
  * Returns zero on success, or a negative error code.  On an error, the
  * connection is broken and the caller must stop transmitting iso packets.
@@ -242,7 +244,7 @@ int cmp_connection_update(struct cmp_connection *c)
 	if (err < 0)
 		goto err_unconnect;
 
-	err = pcr_modify(c, ipcr_set_modify, ipcr_set_check,
+	err = pcr_modify(c, ipcr_set_modify, pcr_set_check,
 			 SUCCEED_ON_BUS_RESET);
 	if (err < 0)
 		goto err_resources;
@@ -261,19 +263,18 @@ err_unconnect:
 }
 EXPORT_SYMBOL(cmp_connection_update);
 
-
-static __be32 ipcr_break_modify(struct cmp_connection *c, __be32 ipcr)
+static __be32 pcr_break_modify(struct cmp_connection *c, __be32 pcr)
 {
-	return ipcr & ~cpu_to_be32(IPCR_BCAST_CONN | IPCR_P2P_CONN_MASK);
+	return pcr & ~cpu_to_be32(PCR_BCAST_CONN | PCR_P2P_CONN_MASK);
 }
 
 /**
  * cmp_connection_break - break the connection to the target
  * @c: the connection manager
  *
- * This function deactives the connection in the target's input plug control
- * register, and frees the isochronous resources of the connection.  Before
- * calling this function, the caller should cease transmitting packets.
+ * This function deactives the connection in the target's input/output plug
+ * control register, and frees the isochronous resources of the connection.
+ * Before calling this function, the caller should cease transmitting packets.
  */
 void cmp_connection_break(struct cmp_connection *c)
 {
@@ -286,7 +287,7 @@ void cmp_connection_break(struct cmp_connection *c)
 		return;
 	}
 
-	err = pcr_modify(c, ipcr_break_modify, NULL, SUCCEED_ON_BUS_RESET);
+	err = pcr_modify(c, pcr_break_modify, NULL, SUCCEED_ON_BUS_RESET);
 	if (err < 0)
 		cmp_error(c, "plug is still connected\n");
 
diff --git a/sound/firewire/cmp.h b/sound/firewire/cmp.h
index f47de08..2320cd4 100644
--- a/sound/firewire/cmp.h
+++ b/sound/firewire/cmp.h
@@ -11,8 +11,8 @@ struct fw_unit;
  * struct cmp_connection - manages an isochronous connection to a device
  * @speed: the connection's actual speed
  *
- * This structure manages (using CMP) an isochronous stream from the local
- * computer to a device's input plug (iPCR).
+ * This structure manages (using CMP) an isochronous stream between the local
+ * computer and a device's input plug (iPCR) and output plug (oPCR).
  *
  * There is no corresponding oPCR created on the local computer, so it is not
  * possible to overlay connections on top of this one.
@@ -30,7 +30,7 @@ struct cmp_connection {
 
 int cmp_connection_init(struct cmp_connection *connection,
 			struct fw_unit *unit,
-			unsigned int ipcr_index);
+			unsigned int pcr_index);
 void cmp_connection_destroy(struct cmp_connection *connection);
 
 int cmp_connection_establish(struct cmp_connection *connection,
