ALSA: seq: Add port inactive flag

This extends the ALSA sequencer port capability bit to indicate the
"inactive" flag.  When this flag is set, the port is essentially
invisible, and doesn't appear in the port query ioctls, while the
direct access and the connection to this port are still allowed.  The
active/inactive state can be flipped dynamically, so that it can be
visible at any time later.

This feature is introduced basically for UMP; some UMP Groups in a UMP
Block may be unassigned, hence those are practically invisible.  On
ALSA sequencer, the corresponding sequencer ports will get this new
"inactive" flag to indicate the invisible state.

Reviewed-by: Jaroslav Kysela <perex@perex.cz>
Link: https://lore.kernel.org/r/20230523075358.9672-27-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

include/uapi/sound/asequencer.h

@@ -427,6 +427,7 @@ struct snd_seq_remove_events {
 #define SNDRV_SEQ_PORT_CAP_SUBS_READ	(1<<5)	/* allow read subscription */
 #define SNDRV_SEQ_PORT_CAP_SUBS_WRITE	(1<<6)	/* allow write subscription */
 #define SNDRV_SEQ_PORT_CAP_NO_EXPORT	(1<<7)	/* routing not allowed */
+#define SNDRV_SEQ_PORT_CAP_INACTIVE	(1<<8)	/* inactive port */
 
 	/* port type */
 #define SNDRV_SEQ_PORT_TYPE_SPECIFIC	(1<<0)	/* hardware specific */

sound/core/seq/seq_clientmgr.c

@@ -2416,6 +2416,8 @@ static void snd_seq_info_dump_ports(struct snd_info_buffer *buffer,
 
 	mutex_lock(&client->ports_mutex);
 	list_for_each_entry(p, &client->ports_list_head, list) {
+		if (p->capability & SNDRV_SEQ_PORT_CAP_INACTIVE)
+			continue;
 		snd_iprintf(buffer, "  Port %3d : \"%s\" (%c%c%c%c)\n",
 			    p->addr.port, p->name,
 			    FLAG_PERM_RD(p->capability),

sound/core/seq/seq_ports.c

@@ -69,11 +69,15 @@ struct snd_seq_client_port *snd_seq_port_query_nearest(struct snd_seq_client *cl
 {
 	int num;
 	struct snd_seq_client_port *port, *found;
+	bool check_inactive = (pinfo->capability & SNDRV_SEQ_PORT_CAP_INACTIVE);
 
 	num = pinfo->addr.port;
 	found = NULL;
 	read_lock(&client->ports_lock);
 	list_for_each_entry(port, &client->ports_list_head, list) {
+		if ((port->capability & SNDRV_SEQ_PORT_CAP_INACTIVE) &&
+		    !check_inactive)
+			continue; /* skip inactive ports */
 		if (port->addr.port < num)
 			continue;
 		if (port->addr.port == num) {