core: new 'rpmsg' subsystem

Most older Qualcomm SoCs (e.g. MSM8916, MSM8974, ...) communicate with
the integrated modem via shared memory (SMD channels). This is similar
to QRTR on newer SoCs, but without the "network" layer. In fact, the
older SoCs also have QRTR, but the modem QMI services are not exposed
there.

The mainline Linux kernel exposes SMD channels via the "remote processor
messaging bus" (rpmsg). Through special IOCTL calls it is possible to
create a char device for a rpmsg/SMD channel. We can then use these to
send QMI/AT messages to the modem, much like the ordinary serial char
devices when using a Qualcomm modem through USB.

This commit introduces support for the new 'rpmsg' subsystem, which
allows exporting QMI-capable and AT-capable ports.

By default NO rpmsg port is flagged as candidate, it is assumed that
the plugin adding support for the rpmsg subsystem will add specific
rules to do so (e.g. so that non-modem ports are explicitly not
flagged as candidate).

All rpmsg ports will be probed for AT or QMI capabilities, unless
explicit port type hints (e.g. ID_MM_PORT_TYPE_QMI or
ID_MM_PORT_TYPE_AT_PRIMARY) are set.

These changes are highly based on the initial integration work done by
Stephan Gerhold <stephan@gerhold.net> in postmarketOS, see:
  https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/merge_requests/363

cli/mmcli-manager.c

@@ -444,7 +444,7 @@ get_manager_ready (GObject      *source,
 
 #if defined WITH_UDEV
     if (report_kernel_event_auto_scan) {
-        const gchar *subsys[] = { "tty", "usbmisc", "net", NULL };
+        const gchar *subsys[] = { "tty", "usbmisc", "net", "rpmsg", NULL };
         guint i;
 
         ctx->udev = g_udev_client_new (subsys);

src/mm-base-modem.c

@@ -237,6 +237,20 @@ base_modem_create_usbmisc_port (MMBaseModem *self,
     return NULL;
 }
 
+static MMPort *
+base_modem_create_rpmsg_port (MMBaseModem *self,
+                              const gchar *name,
+                              MMPortType   ptype)
+{
+#if defined WITH_QMI
+    if (ptype == MM_PORT_TYPE_QMI)
+        return MM_PORT (mm_port_qmi_new (name, MM_PORT_SUBSYS_RPMSG));
+#endif
+    if (ptype == MM_PORT_TYPE_AT)
+        return MM_PORT (mm_port_serial_at_new (name, MM_PORT_SUBSYS_RPMSG));
+    return NULL;
+}
+
 static MMPort *
 base_modem_create_virtual_port (MMBaseModem *self,
                                 const gchar *name)
@@ -278,6 +292,8 @@ mm_base_modem_grab_port (MMBaseModem         *self,
         port = base_modem_create_tty_port (self, name, kernel_device, ptype);
     else if (g_str_equal (subsys, "usbmisc"))
         port = base_modem_create_usbmisc_port (self, name, ptype);
+    else if (g_str_equal (subsys, "rpmsg"))
+        port = base_modem_create_rpmsg_port (self, name, ptype);
     else if (g_str_equal (subsys, "virtual"))
         port = base_modem_create_virtual_port (self, name);
 
@@ -327,8 +343,6 @@ mm_base_modem_grab_port (MMBaseModem         *self,
     return TRUE;
 }
 
-/******************************************************************************/
-
 gboolean
 mm_base_modem_disable_finish (MMBaseModem   *self,
                               GAsyncResult  *res,

src/mm-filter.c

@@ -199,6 +199,13 @@ mm_filter_port (MMFilter        *self,
         return TRUE;
     }
 
+    /* If this is a rpmsg channel device, we always allow it */
+    if ((self->priv->enabled_rules & MM_FILTER_RULE_RPMSG) &&
+        (g_strcmp0 (subsystem, "rpmsg") == 0)) {
+        mm_obj_dbg (self, "(%s/%s) port allowed: rpmsg device", subsystem, name);
+        return TRUE;
+    }
+
     /* If this is a tty device, we may allow it */
     if ((self->priv->enabled_rules & MM_FILTER_RULE_TTY) &&
         (g_strcmp0 (subsystem, "tty") == 0)) {

src/mm-filter.h

@@ -53,15 +53,16 @@ typedef enum { /*< underscore_name=mm_filter_rule >*/
     MM_FILTER_RULE_VIRTUAL               = 1 << 3,
     MM_FILTER_RULE_NET                   = 1 << 4,
     MM_FILTER_RULE_USBMISC               = 1 << 5,
-    MM_FILTER_RULE_TTY                   = 1 << 6,
+    MM_FILTER_RULE_RPMSG                 = 1 << 6,
-    MM_FILTER_RULE_TTY_BLACKLIST         = 1 << 7,
+    MM_FILTER_RULE_TTY                   = 1 << 7,
-    MM_FILTER_RULE_TTY_MANUAL_SCAN_ONLY  = 1 << 8,
+    MM_FILTER_RULE_TTY_BLACKLIST         = 1 << 8,
-    MM_FILTER_RULE_TTY_PLATFORM_DRIVER   = 1 << 9,
+    MM_FILTER_RULE_TTY_MANUAL_SCAN_ONLY  = 1 << 9,
-    MM_FILTER_RULE_TTY_DEFAULT_ALLOWED   = 1 << 10,
+    MM_FILTER_RULE_TTY_PLATFORM_DRIVER   = 1 << 10,
-    MM_FILTER_RULE_TTY_DRIVER            = 1 << 11,
+    MM_FILTER_RULE_TTY_DEFAULT_ALLOWED   = 1 << 11,
-    MM_FILTER_RULE_TTY_ACM_INTERFACE     = 1 << 12,
+    MM_FILTER_RULE_TTY_DRIVER            = 1 << 12,
-    MM_FILTER_RULE_TTY_WITH_NET          = 1 << 13,
+    MM_FILTER_RULE_TTY_ACM_INTERFACE     = 1 << 13,
-    MM_FILTER_RULE_TTY_DEFAULT_FORBIDDEN = 1 << 14,
+    MM_FILTER_RULE_TTY_WITH_NET          = 1 << 14,
+    MM_FILTER_RULE_TTY_DEFAULT_FORBIDDEN = 1 << 15,
 } MMFilterRule;
 
 #define MM_FILTER_RULE_ALL                  \
@@ -71,6 +72,7 @@ typedef enum { /*< underscore_name=mm_filter_rule >*/
      MM_FILTER_RULE_VIRTUAL               | \
      MM_FILTER_RULE_NET                   | \
      MM_FILTER_RULE_USBMISC               | \
+     MM_FILTER_RULE_RPMSG                 | \
      MM_FILTER_RULE_TTY                   | \
      MM_FILTER_RULE_TTY_BLACKLIST         | \
      MM_FILTER_RULE_TTY_MANUAL_SCAN_ONLY  | \
@@ -89,6 +91,7 @@ typedef enum { /*< underscore_name=mm_filter_rule >*/
      MM_FILTER_RULE_VIRTUAL              | \
      MM_FILTER_RULE_NET                  | \
      MM_FILTER_RULE_USBMISC              | \
+     MM_FILTER_RULE_RPMSG                | \
      MM_FILTER_RULE_TTY                  | \
      MM_FILTER_RULE_TTY_BLACKLIST        | \
      MM_FILTER_RULE_TTY_MANUAL_SCAN_ONLY | \
@@ -104,6 +107,7 @@ typedef enum { /*< underscore_name=mm_filter_rule >*/
      MM_FILTER_RULE_VIRTUAL               | \
      MM_FILTER_RULE_NET                   | \
      MM_FILTER_RULE_USBMISC               | \
+     MM_FILTER_RULE_RPMSG                 | \
      MM_FILTER_RULE_TTY                   | \
      MM_FILTER_RULE_TTY_PLATFORM_DRIVER   | \
      MM_FILTER_RULE_TTY_DRIVER            | \
@@ -120,6 +124,7 @@ typedef enum { /*< underscore_name=mm_filter_rule >*/
      MM_FILTER_RULE_VIRTUAL               | \
      MM_FILTER_RULE_NET                   | \
      MM_FILTER_RULE_USBMISC               | \
+     MM_FILTER_RULE_RPMSG                 | \
      MM_FILTER_RULE_TTY                   | \
      MM_FILTER_RULE_TTY_BLACKLIST         | \
      MM_FILTER_RULE_TTY_MANUAL_SCAN_ONLY  | \

src/mm-plugin.c

@@ -781,6 +781,11 @@ mm_plugin_supports_port (MMPlugin            *self,
             probe_run_flags |= MM_PORT_PROBE_MBIM;
         else
             probe_run_flags |= MM_PORT_PROBE_AT;
+    } else if (g_str_equal (mm_kernel_device_get_subsystem (port), "rpmsg")) {
+        if (self->priv->at)
+            probe_run_flags |= MM_PORT_PROBE_AT;
+        if (self->priv->qmi)
+            probe_run_flags |= MM_PORT_PROBE_QMI;
     }
 
     /* For potential AT ports, check for more things */

src/mm-port-probe.c

@@ -491,16 +491,22 @@ wdm_probe_qmi (MMPortProbe *self)
     ctx = g_task_get_task_data (self->priv->task);
 
 #if defined WITH_QMI
-    mm_obj_dbg (self, "probing QMI...");
+    {
+        MMPortSubsys subsys = MM_PORT_SUBSYS_USBMISC;
 
-    /* Create a port and try to open it */
+        mm_obj_dbg (self, "probing QMI...");
-    ctx->port_qmi = mm_port_qmi_new (mm_kernel_device_get_name (self->priv->port),
+
-                                     MM_PORT_SUBSYS_USBMISC);
+        if (g_str_equal (mm_kernel_device_get_subsystem (self->priv->port), "rpmsg"))
-    mm_port_qmi_open (ctx->port_qmi,
+            subsys = MM_PORT_SUBSYS_RPMSG;
-                      FALSE,
+
-                      NULL,
+        /* Create a port and try to open it */
-                      (GAsyncReadyCallback) port_qmi_open_ready,
+        ctx->port_qmi = mm_port_qmi_new (mm_kernel_device_get_name (self->priv->port), subsys);
-                      self);
+        mm_port_qmi_open (ctx->port_qmi,
+                          FALSE,
+                          NULL,
+                          (GAsyncReadyCallback) port_qmi_open_ready,
+                          self);
+    }
 #else
     /* If not compiled with QMI support, just assume we won't have any QMI port */
     mm_port_probe_set_result_qmi (self, FALSE);
@@ -1273,6 +1279,8 @@ serial_open_at (MMPortProbe *self)
 
         if (g_str_equal (mm_kernel_device_get_subsystem (self->priv->port), "usbmisc"))
             subsys = MM_PORT_SUBSYS_USBMISC;
+        else if (g_str_equal (mm_kernel_device_get_subsystem (self->priv->port), "rpmsg"))
+            subsys = MM_PORT_SUBSYS_RPMSG;
 
         ctx->serial = MM_PORT_SERIAL (mm_port_serial_at_new (mm_kernel_device_get_name (self->priv->port), subsys));
         if (!ctx->serial) {

src/mm-port.h

@@ -28,8 +28,8 @@ typedef enum { /*< underscore_name=mm_port_subsys >*/
     MM_PORT_SUBSYS_NET,
     MM_PORT_SUBSYS_USBMISC,
     MM_PORT_SUBSYS_UNIX,
-
+    MM_PORT_SUBSYS_RPMSG,
-    MM_PORT_SUBSYS_LAST = MM_PORT_SUBSYS_UNIX /*< skip >*/
+    MM_PORT_SUBSYS_LAST = MM_PORT_SUBSYS_RPMSG /*< skip >*/
 } MMPortSubsys;
 
 typedef enum { /*< underscore_name=mm_port_type >*/