port-serial: add serial port command scheduler

Add an interface and implementation for a port scheduler that round-
robins between ports the scheduler is attached to, serializing command
execution among one or more MMPortSerial instances.

Theory of operation:

Sources (e.g. MMPort subclasses) register themselves with the scheduler.

Each source notifies the scheduler whenever its command queue depth changes,
for example when new commands are submitted, when commands are completed,
or when commands are canceled.

The scheduler will round-robin between all sources with pending commands,
sleeping when there are no pending commands from any source.

For each source with a pending command the scheduler will emit the
'send-command' signal with that source's ID. The given source should
send the next command in its queue to the modem.

When that command is finished (either successfully or with an error/timeout)
the source must call mm_port_scheduler_notify_command_done() to notify the
scheduler that it may advance to the next source with a pending command, if
any. If the 'send-command' signal and the notify_command_done() call are not
balanced the scheduler may stall.

Signed-off-by: Dan Williams <dan@ioncontrol.co>

1 files changed, 357 insertions, 0 deletions

diff --git a/src/mm-port-scheduler-rr.c b/src/mm-port-scheduler-rr.c
new file mode 100644
index 00000000..8d6f8195
--- /dev/null
+++ b/src/mm-port-scheduler-rr.c
@@ -0,0 +1,357 @@
+/* -*- Mode: C; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details:
+ *
+ * Copyright (C) 2025 Dan Williams <dan@ioncontrol.co>
+ */
+
+#include "mm-port-scheduler-rr.h"
+#include "mm-log-object.h"
+
+/* Theory of operation:
+ *
+ * Sources (e.g. MMPort subclasses) register themselves with the scheduler.
+ *
+ * Each source notifies the scheduler whenever its command queue depth changes,
+ * for example when new commands are submitted, when commands are completed,
+ * or when commands are canceled.
+ *
+ * The scheduler will round-robin between all sources with pending commands,
+ * sleeping when there are no pending commands from any source.
+ *
+ * For each source with a pending command the scheduler will emit the
+ * 'send-command' signal with that source's ID. The given source should
+ * send the next command in its queue to the modem.
+ *
+ * When that command is finished (either successfully or with an error/timeout)
+ * the source must call mm_port_scheduler_notify_command_done() to notify the
+ * scheduler that it may advance to the next source with a pending command, if
+ * any. If the 'send-command' signal and the notify_command_done() call are not
+ * balanced the scheduler may stall.
+ */
+
+static void mm_port_scheduler_iface_init (MMPortSchedulerInterface *iface);
+
+struct _MMPortSchedulerRRPrivate {
+    GPtrArray *sources;
+    guint      cur_source;
+    gboolean   in_command;
+    guint      next_pending_id;
+
+    /* Delay between allowing ports to send commands, in ms */
+    guint inter_port_delay;
+};
+
+enum {
+    PROP_0,
+    PROP_INTER_PORT_DELAY,
+
+    LAST_PROP
+};
+
+static guint send_command_signal = 0;
+
+G_DEFINE_TYPE_WITH_CODE (MMPortSchedulerRR, mm_port_scheduler_rr, G_TYPE_OBJECT,
+                         G_ADD_PRIVATE (MMPortSchedulerRR)
+                         G_IMPLEMENT_INTERFACE (MM_TYPE_PORT_SCHEDULER,
+                                                mm_port_scheduler_iface_init))
+
+/*****************************************************************************/
+
+typedef struct {
+    gpointer  id;
+    gchar    *tag; /* e.g. port name */
+    guint     num_pending;
+} Source;
+
+static void
+source_free (Source *s)
+{
+    g_free (s->tag);
+    g_slice_free (Source, s);
+}
+
+static Source *
+find_source (MMPortSchedulerRR *self,
+             gpointer           source_id,
+             guint             *out_idx)
+{
+    guint i;
+
+    for (i = 0; i < self->priv->sources->len; i++) {
+        Source *s;
+
+        s = g_ptr_array_index (self->priv->sources, i);
+        if (s->id == source_id) {
+            if (out_idx)
+                *out_idx = i;
+            return s;
+        }
+    }
+
+    return NULL;
+}
+
+static Source *
+find_next_source (MMPortSchedulerRR *self,
+                  guint             *out_idx)
+{
+    guint i, idx;
+
+    /* Starting at the source *after* the current source, advance through
+     * the entire array and back to the current source (in case only the
+     * current source has pending commands) to find the next source with
+     * a pending command.
+     */
+    for (i = 0, idx = self->priv->cur_source + 1;
+         i < self->priv->sources->len;
+         i++, idx++) {
+        Source *s;
+
+        /* Wrap around */
+        if (idx >= self->priv->sources->len)
+            idx = 0;
+
+        s = g_ptr_array_index (self->priv->sources, idx);
+        if (s->num_pending > 0) {
+            if (out_idx)
+                *out_idx = idx;
+            return s;
+        }
+    }
+
+    return NULL;
+}
+
+static void schedule_next_command (MMPortSchedulerRR *self);
+
+static gboolean
+run_next_command (MMPortSchedulerRR *self)
+{
+    self->priv->next_pending_id = 0;
+
+    if (find_next_source (self, &self->priv->cur_source)) {
+        Source *s;
+
+        s = g_ptr_array_index (self->priv->sources, self->priv->cur_source);
+        /* If this source has a pending command, run it. */
+        self->priv->in_command = TRUE;
+        g_signal_emit (MM_PORT_SCHEDULER (self),
+                       send_command_signal,
+                       0,
+                       s->id);
+    }
+
+    return G_SOURCE_REMOVE;
+}
+
+static void
+schedule_next_command (MMPortSchedulerRR *self)
+{
+    guint next_idx = 0;
+    guint delay = 0;
+
+    if (self->priv->next_pending_id || self->priv->in_command || !find_next_source (self, &next_idx))
+        return;
+
+    /* Only delay next command if we change sources and this isn't the
+     * first time we're running a command.
+     */
+    if (next_idx != self->priv->cur_source && self->priv->cur_source < self->priv->sources->len)
+        delay = self->priv->inter_port_delay;
+    self->priv->next_pending_id = g_timeout_add (delay, (GSourceFunc) run_next_command, self);
+}
+
+static void
+register_source (MMPortScheduler *scheduler,
+                 gpointer         source_id,
+                 const gchar     *tag)
+{
+    MMPortSchedulerRR *self = MM_PORT_SCHEDULER_RR (scheduler);
+    Source *s;
+
+    g_assert (source_id != NULL);
+
+    s = find_source (self, source_id, NULL);
+    if (!s) {
+        s = g_slice_new0 (Source);
+        s->id = source_id;
+        s->tag = g_strdup (tag);
+        g_ptr_array_add (self->priv->sources, s);
+    }
+}
+
+static void
+unregister_source (MMPortScheduler *scheduler, gpointer source_id)
+{
+    MMPortSchedulerRR *self = MM_PORT_SCHEDULER_RR (scheduler);
+    Source *s;
+    guint   idx = 0;
+
+    g_assert (source_id != NULL);
+
+    s = find_source (self, source_id, &idx);
+    if (s) {
+        g_ptr_array_remove_index (self->priv->sources, idx);
+
+        /* If we just removed the current source, advance to the next one */
+        if (self->priv->cur_source == idx)
+            schedule_next_command (self);
+    }
+}
+
+static void
+notify_num_pending (MMPortScheduler *scheduler,
+                    gpointer         source_id,
+                    guint            num_pending)
+{
+    MMPortSchedulerRR *self = MM_PORT_SCHEDULER_RR (scheduler);
+    Source *s;
+
+    g_assert (source_id != NULL);
+
+    s = find_source (self, source_id, NULL);
+    if (s && s->num_pending != num_pending) {
+        s->num_pending = num_pending;
+        schedule_next_command (self);
+    }
+}
+
+static void
+notify_command_done (MMPortScheduler *scheduler,
+                     gpointer         source_id,
+                     guint            num_pending)
+{
+    MMPortSchedulerRR *self = MM_PORT_SCHEDULER_RR (scheduler);
+    Source            *s;
+    guint              idx = 0;
+
+    g_assert (source_id != NULL);
+
+    s = find_source (self, source_id, &idx);
+    if (!s) {
+        mm_obj_warn (self, "unknown source %p notified command-done", source_id);
+        return;
+    }
+
+    /* Only the current source gets to call this function */
+    if (self->priv->cur_source != idx) {
+        mm_obj_warn (self,
+                     "source %p notified command-done but not active source",
+                     source_id);
+        return;
+    }
+
+    self->priv->in_command = FALSE;
+    s->num_pending = num_pending;
+    schedule_next_command (self);
+}
+
+/*****************************************************************************/
+
+MMPortSchedulerRR *
+mm_port_scheduler_rr_new (void)
+{
+    return MM_PORT_SCHEDULER_RR (g_object_new (MM_TYPE_PORT_SCHEDULER_RR, NULL));
+}
+
+static void
+get_property (GObject *object,
+              guint prop_id,
+              GValue *value,
+              GParamSpec *pspec)
+{
+    MMPortSchedulerRR *self = MM_PORT_SCHEDULER_RR (object);
+
+    switch (prop_id) {
+    case PROP_INTER_PORT_DELAY:
+        g_value_set_uint (value, self->priv->inter_port_delay);
+        break;
+    default:
+        G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
+        break;
+    }
+}
+
+static void
+set_property (GObject *object,
+              guint prop_id,
+              const GValue *value,
+              GParamSpec *pspec)
+{
+    MMPortSchedulerRR *self = MM_PORT_SCHEDULER_RR (object);
+
+    switch (prop_id) {
+    case PROP_INTER_PORT_DELAY:
+        self->priv->inter_port_delay = g_value_get_uint (value);
+        break;
+    default:
+        G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
+        break;
+    }
+}
+
+static void
+mm_port_scheduler_iface_init (MMPortSchedulerInterface *scheduler_iface)
+{
+    scheduler_iface->register_source = register_source;
+    scheduler_iface->unregister_source = unregister_source;
+    scheduler_iface->notify_num_pending = notify_num_pending;
+    scheduler_iface->notify_command_done = notify_command_done;
+
+    send_command_signal = g_signal_lookup (MM_PORT_SCHEDULER_SIGNAL_SEND_COMMAND,
+                                           MM_TYPE_PORT_SCHEDULER);
+}
+
+static void
+mm_port_scheduler_rr_init (MMPortSchedulerRR *self)
+{
+    self->priv = G_TYPE_INSTANCE_GET_PRIVATE (self,
+                                              MM_TYPE_PORT_SCHEDULER_RR,
+                                              MMPortSchedulerRRPrivate);
+    self->priv->sources = g_ptr_array_new_full (2, (GDestroyNotify) source_free);
+    self->priv->cur_source = G_MAXUINT32;
+}
+
+static void
+dispose (GObject *object)
+{
+    MMPortSchedulerRR *self = MM_PORT_SCHEDULER_RR (object);
+
+    if (self->priv->next_pending_id) {
+        g_source_remove (self->priv->next_pending_id);
+        self->priv->next_pending_id = 0;
+    }
+
+    g_assert (self->priv->sources->len == 0);
+    g_ptr_array_free (self->priv->sources, TRUE);
+
+    G_OBJECT_CLASS (mm_port_scheduler_rr_parent_class)->dispose (object);
+}
+
+static void
+mm_port_scheduler_rr_class_init (MMPortSchedulerRRClass *klass)
+{
+    GObjectClass *object_class = G_OBJECT_CLASS (klass);
+
+    /* Virtual methods */
+    object_class->set_property = set_property;
+    object_class->get_property = get_property;
+    object_class->dispose = dispose;
+
+    g_object_class_install_property
+        (object_class, PROP_INTER_PORT_DELAY,
+         g_param_spec_uint (MM_PORT_SCHEDULER_RR_INTER_PORT_DELAY,
+                            "Inter-port Delay",
+                            "Inter-port delay in ms",
+                            0, G_MAXUINT, 0,
+                            G_PARAM_READWRITE));
+}