ALSA: firewire-lib: Add a new function to check others' connection

Plug Control Registers have two fields related to the number of established
connections, one is 'Broadcast connection counter' and another is
'Point-to-point connection counter'. The driver can know there are established
connections or not to check these fields.

This commit is for considering about JACK/FFADO streaming. Currently, when
JACK/FFADO starts its streaming to the device, cmp_connection_establish() is
failed expectedly. This seems to be enough but there are some devices which
needs to change sampling frequency before trying to establish connections.
For such devices, this functionality is needed.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/firewire/cmp.c

@@ -151,6 +151,24 @@ int cmp_connection_init(struct cmp_connection *c,
 }
 EXPORT_SYMBOL(cmp_connection_init);
 
+/**
+ * cmp_connection_check_used - check connection is already esablished or not
+ * @c: the connection manager to be checked
+ */
+int cmp_connection_check_used(struct cmp_connection *c, bool *used)
+{
+	__be32 pcr;
+	int err;
+
+	err = snd_fw_transaction(
+			c->resources.unit, TCODE_READ_QUADLET_REQUEST,
+			pcr_address(c), &pcr, 4, 0);
+	if (err >= 0)
+		*used = (pcr & cpu_to_be32(PCR_BCAST_CONN | PCR_P2P_CONN_MASK));
+	return err;
+}
+EXPORT_SYMBOL(cmp_connection_check_used);
+
 /**
  * cmp_connection_destroy - free connection manager resources
  * @c: the connection manager

sound/firewire/cmp.h

@@ -38,6 +38,7 @@ int cmp_connection_init(struct cmp_connection *connection,
 			struct fw_unit *unit,
 			enum cmp_direction direction,
 			unsigned int pcr_index);
+int cmp_connection_check_used(struct cmp_connection *connection, bool *used);
 void cmp_connection_destroy(struct cmp_connection *connection);
 
 int cmp_connection_establish(struct cmp_connection *connection,