kmssink: Add "restore-crtc" property

This adds "restore-crtc" property using which one
can restore previous crtc mode.

By default it is enabled, if CRTC was already
active with a valid mode and kmssink set a new mode
on CRTC using force-modesetting.

This helps user restore previous crtc mode and get
the previous session back after running a kmssink
pipeline involving a force-modesetting.

For e.g. When running a kmssink pipeline on rpi
using force-modesetting on tty console, it was giving
a blank screen after pipeline, and now with help of restore-crtc
functionality, CRTC is set with previous crtc mode
previously active on tty console.

Edited-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>

https://bugzilla.gnome.org/show_bug.cgi?id=797025

sys/kms/gstkmssink.c

@@ -90,6 +90,7 @@ enum
   PROP_CONNECTOR_ID,
   PROP_PLANE_ID,
   PROP_FORCE_MODESETTING,
+  PROP_RESTORE_CRTC,
   PROP_CAN_SCALE,
   PROP_DISPLAY_WIDTH,
   PROP_DISPLAY_HEIGHT,
@@ -740,6 +741,10 @@ gst_kms_sink_start (GstBaseSink * bsink)
     universal_planes = TRUE;
   }
 
+  if (crtc->mode_valid && self->modesetting_enabled && self->restore_crtc) {
+    self->saved_crtc = (drmModeCrtc *) crtc;
+  }
+
 retry_find_plane:
   if (universal_planes &&
       drmSetClientCap (self->fd, DRM_CLIENT_CAP_UNIVERSAL_PLANES, 1))
@@ -805,7 +810,7 @@ bail:
     drmModeFreePlane (plane);
   if (pres)
     drmModeFreePlaneResources (pres);
-  if (crtc)
+  if (crtc != self->saved_crtc)
     drmModeFreeCrtc (crtc);
   if (conn)
     drmModeFreeConnector (conn);
@@ -890,6 +895,7 @@ static gboolean
 gst_kms_sink_stop (GstBaseSink * bsink)
 {
   GstKMSSink *self;
+  int err;
 
   self = GST_KMS_SINK (bsink);
 
@@ -905,6 +911,19 @@ gst_kms_sink_stop (GstBaseSink * bsink)
   gst_poll_restart (self->poll);
   gst_poll_fd_init (&self->pollfd);
 
+  if (self->saved_crtc) {
+    drmModeCrtc *crtc = (drmModeCrtc *) self->saved_crtc;
+
+    err = drmModeSetCrtc (self->fd, crtc->crtc_id, crtc->buffer_id, crtc->x,
+        crtc->y, (uint32_t *) & self->conn_id, 1, &crtc->mode);
+    if (err)
+      GST_ERROR_OBJECT (self, "Failed to restore previous CRTC mode: %s",
+          g_strerror (errno));
+
+    drmModeFreeCrtc (crtc);
+    self->saved_crtc = NULL;
+  }
+
   if (self->fd >= 0) {
     drmClose (self->fd);
     self->fd = -1;
@@ -1723,6 +1742,9 @@ gst_kms_sink_set_property (GObject * object, guint prop_id,
     case PROP_FORCE_MODESETTING:
       sink->modesetting_enabled = g_value_get_boolean (value);
       break;
+    case PROP_RESTORE_CRTC:
+      sink->restore_crtc = g_value_get_boolean (value);
+      break;
     case PROP_CAN_SCALE:
       sink->can_scale = g_value_get_boolean (value);
       break;
@@ -1777,6 +1799,9 @@ gst_kms_sink_get_property (GObject * object, guint prop_id,
     case PROP_FORCE_MODESETTING:
       g_value_set_boolean (value, sink->modesetting_enabled);
       break;
+    case PROP_RESTORE_CRTC:
+      g_value_set_boolean (value, sink->restore_crtc);
+      break;
     case PROP_CAN_SCALE:
       g_value_set_boolean (value, sink->can_scale);
       break;
@@ -1920,6 +1945,19 @@ gst_kms_sink_class_init (GstKMSSinkClass * klass)
       "When enabled, the sink try to configure the display mode", FALSE,
       G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS | G_PARAM_CONSTRUCT);
 
+  /**
+   * kmssink:restore-crtc:
+   *
+   * Restore previous CRTC setting if new CRTC mode was set forcefully.
+   * By default this is enabled if user set CRTC with a new mode on an already
+   * active CRTC wich was having a valid mode.
+   */
+  g_properties[PROP_RESTORE_CRTC] =
+      g_param_spec_boolean ("restore-crtc", "Restore CRTC mode",
+      "When enabled and CRTC was set with a new mode, previous CRTC mode will"
+      "be restored when going to NULL state.", TRUE,
+      G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS | G_PARAM_CONSTRUCT);
+
   /**
    * kmssink:can-scale:
    *

sys/kms/gstkmssink.h

@@ -65,6 +65,7 @@ struct _GstKMSSink {
   gboolean can_scale;
 
   gboolean modesetting_enabled;
+  gboolean restore_crtc;
   GstStructure *connector_props;
   GstStructure *plane_props;
 
@@ -79,7 +80,7 @@ struct _GstKMSSink {
   gchar *bus_id;
 
   guint32 mm_width, mm_height;
-
+  gpointer saved_crtc;
   GstPoll *poll;
   GstPollFD pollfd;