Input: serio - support multiple child devices per single parent

Some (rare) serio devices need to have multiple serio children. One of
the examples is PS/2 multiplexer present on several TQC STKxxx boards,
which connect PS/2 keyboard and mouse to single tty port.

Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

3 files changed, 86 insertions, 46 deletions

diff --git a/drivers/input/mouse/psmouse-base.c b/drivers/input/mouse/psmouse-base.c
index 73a7af2542a8..cd9d0c97e429 100644
--- a/drivers/input/mouse/psmouse-base.c
+++ b/drivers/input/mouse/psmouse-base.c
@@ -1584,10 +1584,10 @@ static ssize_t psmouse_attr_set_protocol(struct psmouse *psmouse, void *data, co
         if (!new_dev)
                 return -ENOMEM;
 
-        while (serio->child) {
+        while (!list_empty(&serio->children)) {
                 if (++retry > 3) {
                         printk(KERN_WARNING
-                                "psmouse: failed to destroy child port, "
+                                "psmouse: failed to destroy children ports, "
                                 "protocol change aborted.\n");
                         input_free_device(new_dev);
                         return -EIO;
diff --git a/drivers/input/serio/serio.c b/drivers/input/serio/serio.c
index 8a426375fcb3..405bf214527c 100644
--- a/drivers/input/serio/serio.c
+++ b/drivers/input/serio/serio.c
@@ -55,7 +55,7 @@ static struct bus_type serio_bus;
 static void serio_add_port(struct serio *serio);
 static int serio_reconnect_port(struct serio *serio);
 static void serio_disconnect_port(struct serio *serio);
-static void serio_reconnect_chain(struct serio *serio);
+static void serio_reconnect_subtree(struct serio *serio);
 static void serio_attach_driver(struct serio_driver *drv);
 
 static int serio_connect_driver(struct serio *serio, struct serio_driver *drv)
@@ -151,7 +151,7 @@ static void serio_find_driver(struct serio *serio)
 enum serio_event_type {
         SERIO_RESCAN_PORT,
         SERIO_RECONNECT_PORT,
-        SERIO_RECONNECT_CHAIN,
+        SERIO_RECONNECT_SUBTREE,
         SERIO_REGISTER_PORT,
         SERIO_ATTACH_DRIVER,
 };
@@ -291,8 +291,8 @@ static void serio_handle_event(void)
                         serio_find_driver(event->object);
                         break;
 
-                case SERIO_RECONNECT_CHAIN:
-                        serio_reconnect_chain(event->object);
+                case SERIO_RECONNECT_SUBTREE:
+                        serio_reconnect_subtree(event->object);
                         break;
 
                 case SERIO_ATTACH_DRIVER:
@@ -329,12 +329,10 @@ static void serio_remove_pending_events(void *object)
 }
 
 /*
- * Destroy child serio port (if any) that has not been fully registered yet.
+ * Locate child serio port (if any) that has not been fully registered yet.
  *
- * Note that we rely on the fact that port can have only one child and therefore
- * only one child registration request can be pending. Additionally, children
- * are registered by driver's connect() handler so there can't be a grandchild
- * pending registration together with a child.
+ * Children are registered by driver's connect() handler so there can't be a
+ * grandchild pending registration together with a child.
  */
 static struct serio *serio_get_pending_child(struct serio *parent)
 {
@@ -448,7 +446,7 @@ static ssize_t serio_rebind_driver(struct device *dev, struct device_attribute *
         if (!strncmp(buf, "none", count)) {
                 serio_disconnect_port(serio);
         } else if (!strncmp(buf, "reconnect", count)) {
-                serio_reconnect_chain(serio);
+                serio_reconnect_subtree(serio);
         } else if (!strncmp(buf, "rescan", count)) {
                 serio_disconnect_port(serio);
                 serio_find_driver(serio);
@@ -515,6 +513,8 @@ static void serio_init_port(struct serio *serio)
         __module_get(THIS_MODULE);
 
         INIT_LIST_HEAD(&serio->node);
+        INIT_LIST_HEAD(&serio->child_node);
+        INIT_LIST_HEAD(&serio->children);
         spin_lock_init(&serio->lock);
         mutex_init(&serio->drv_mutex);
         device_initialize(&serio->dev);
@@ -537,12 +537,13 @@ static void serio_init_port(struct serio *serio)
  */
 static void serio_add_port(struct serio *serio)
 {
+        struct serio *parent = serio->parent;
         int error;
 
-        if (serio->parent) {
-                serio_pause_rx(serio->parent);
-                serio->parent->child = serio;
-                serio_continue_rx(serio->parent);
+        if (parent) {
+                serio_pause_rx(parent);
+                list_add_tail(&serio->child_node, &parent->children);
+                serio_continue_rx(parent);
         }
 
         list_add_tail(&serio->node, &serio_list);
@@ -558,15 +559,14 @@ static void serio_add_port(struct serio *serio)
 }
 
 /*
- * serio_destroy_port() completes deregistration process and removes
+ * serio_destroy_port() completes unregistration process and removes
  * port from the system
  */
 static void serio_destroy_port(struct serio *serio)
 {
         struct serio *child;
 
-        child = serio_get_pending_child(serio);
-        if (child) {
+        while ((child = serio_get_pending_child(serio)) != NULL) {
                 serio_remove_pending_events(child);
                 put_device(&child->dev);
         }
@@ -576,7 +576,7 @@ static void serio_destroy_port(struct serio *serio)
 
         if (serio->parent) {
                 serio_pause_rx(serio->parent);
-                serio->parent->child = NULL;
+                list_del_init(&serio->child_node);
                 serio_continue_rx(serio->parent);
                 serio->parent = NULL;
         }
@@ -608,46 +608,82 @@ static int serio_reconnect_port(struct serio *serio)
 }
 
 /*
- * Reconnect serio port and all its children (re-initialize attached devices)
+ * Reconnect serio port and all its children (re-initialize attached
+ * devices).
  */
-static void serio_reconnect_chain(struct serio *serio)
+static void serio_reconnect_subtree(struct serio *root)
 {
+        struct serio *s = root;
+        int error;
+
         do {
-                if (serio_reconnect_port(serio)) {
-                        /* Ok, old children are now gone, we are done */
-                        break;
+                error = serio_reconnect_port(s);
+                if (!error) {
+                        /*
+                         * Reconnect was successful, move on to do the
+                         * first child.
+                         */
+                        if (!list_empty(&s->children)) {
+                                s = list_first_entry(&s->children,
+                                                     struct serio, child_node);
+                                continue;
+                        }
                 }
-                serio = serio->child;
-        } while (serio);
+
+                /*
+                 * Either it was a leaf node or reconnect failed and it
+                 * became a leaf node. Continue reconnecting starting with
+                 * the next sibling of the parent node.
+                 */
+                while (s != root) {
+                        struct serio *parent = s->parent;
+
+                        if (!list_is_last(&s->child_node, &parent->children)) {
+                                s = list_entry(s->child_node.next,
+                                               struct serio, child_node);
+                                break;
+                        }
+
+                        s = parent;
+                }
+        } while (s != root);
 }
 
 /*
  * serio_disconnect_port() unbinds a port from its driver. As a side effect
- * all child ports are unbound and destroyed.
+ * all children ports are unbound and destroyed.
  */
 static void serio_disconnect_port(struct serio *serio)
 {
-        struct serio *s, *parent;
+        struct serio *s = serio;
+
+        /*
+         * Children ports should be disconnected and destroyed
+         * first; we travel the tree in depth-first order.
+         */
+        while (!list_empty(&serio->children)) {
+
+                /* Locate a leaf */
+                while (!list_empty(&s->children))
+                        s = list_first_entry(&s->children,
+                                             struct serio, child_node);
 
-        if (serio->child) {
                 /*
-                 * Children ports should be disconnected and destroyed
-                 * first, staring with the leaf one, since we don't want
-                 * to do recursion
+                 * Prune this leaf node unless it is the one we
+                 * started with.
                  */
-                for (s = serio; s->child; s = s->child)
-                        /* empty */;
-
-                do {
-                        parent = s->parent;
+                if (s != serio) {
+                        struct serio *parent = s->parent;
 
                         device_release_driver(&s->dev);
                         serio_destroy_port(s);
-                } while ((s = parent) != serio);
+
+                        s = parent;
+                }
         }
 
         /*
-         * Ok, no children left, now disconnect this port
+         * OK, no children left, now disconnect this port.
          */
         device_release_driver(&serio->dev);
 }
@@ -660,7 +696,7 @@ EXPORT_SYMBOL(serio_rescan);
 
 void serio_reconnect(struct serio *serio)
 {
-        serio_queue_event(serio, NULL, SERIO_RECONNECT_CHAIN);
+        serio_queue_event(serio, NULL, SERIO_RECONNECT_SUBTREE);
 }
 EXPORT_SYMBOL(serio_reconnect);
 
@@ -688,14 +724,16 @@ void serio_unregister_port(struct serio *serio)
 EXPORT_SYMBOL(serio_unregister_port);
 
 /*
- * Safely unregisters child port if one is present.
+ * Safely unregisters children ports if they are present.
  */
 void serio_unregister_child_port(struct serio *serio)
 {
+        struct serio *s, *next;
+
         mutex_lock(&serio_mutex);
-        if (serio->child) {
-                serio_disconnect_port(serio->child);
-                serio_destroy_port(serio->child);
+        list_for_each_entry_safe(s, next, &serio->children, child_node) {
+                serio_disconnect_port(s);
+                serio_destroy_port(s);
         }
         mutex_unlock(&serio_mutex);
 }
diff --git a/include/linux/serio.h b/include/linux/serio.h
index 111ad501b054..109b237603b6 100644
--- a/include/linux/serio.h
+++ b/include/linux/serio.h
@@ -41,7 +41,9 @@ struct serio {
         int (*start)(struct serio *);
         void (*stop)(struct serio *);
 
-        struct serio *parent, *child;
+        struct serio *parent;
+        struct list_head child_node;    /* Entry in parent->children list */
+        struct list_head children;
         unsigned int depth;             /* level of nesting in serio hierarchy */
 
         struct serio_driver *drv;       /* accessed from interrupt, must be protected by serio->lock and serio->sem */