If the dvb frontend thread starts, the tuner should be switched
to the frontend. Add a code that ensures that this will happen,
using the media controller.

Signed-off-by: Mauro Carvalho Chehab <mche...@osg.samsung.com>

diff --git a/drivers/media/dvb-core/dvb_frontend.c 
b/drivers/media/dvb-core/dvb_frontend.c
index c2c559105f64..04e949ad9722 100644
--- a/drivers/media/dvb-core/dvb_frontend.c
+++ b/drivers/media/dvb-core/dvb_frontend.c
@@ -590,12 +590,99 @@ static void dvb_frontend_wakeup(struct dvb_frontend *fe)
        wake_up_interruptible(&fepriv->wait_queue);
 }
 
+/**
+ * dvb_enable_media_tuner() - tries to enable the DVB tuner
+ *
+ * @fe:                struct dvb_frontend pointer
+ *
+ * This function ensures that just one media tuner is enabled for a given
+ * frontend. It has two different behaviors:
+ * - For trivial devices with just one tuner:
+ *   it just enables the existing tuner->fe link
+ * - For devices with more than one tuner:
+ *   It is up to the driver to implement the logic that will enable one tuner
+ *   and disable the other ones. However, if more than one tuner is enabled for
+ *   the same frontend, it will print an error message and return -EINVAL.
+ *
+ * At return, it will return the error code returned by 
media_entity_setup_link,
+ * or 0 if everything is OK, if no tuner is linked to the frontend or if the
+ * mdev is NULL.
+ */
+static int dvb_enable_media_tuner(struct dvb_frontend *fe)
+{
+#ifdef CONFIG_MEDIA_CONTROLLER
+       struct dvb_frontend_private *fepriv = fe->frontend_priv;
+       struct dvb_adapter *adapter = fe->dvb;
+       struct media_device *mdev = adapter->mdev;
+       struct media_entity  *entity, *source;
+       struct media_link *link, *found_link = NULL;
+       int i, ret, n_links = 0, active_links = 0;
+
+       if (!mdev)
+               return 0;
+
+       entity = fepriv->dvbdev->entity;
+       for (i = 0; i < entity->num_links; i++) {
+               link = &entity->links[i];
+               if (link->sink->entity == entity) {
+                       found_link = link;
+                       n_links++;
+                       if (link->flags & MEDIA_LNK_FL_ENABLED)
+                               active_links++;
+               }
+       }
+
+       if (!n_links || active_links == 1 || !found_link)
+               return 0;
+
+       /*
+        * If a frontend has more than one tuner linked, it is up to the driver
+        * to select with one will be the active one, as the frontend core can't
+        * guess. If the driver doesn't do that, it is a bug.
+        */
+       if (n_links > 1 && active_links != 1) {
+               dev_err(fe->dvb->device,
+                       "WARNING: there are %d active links among %d tuners. 
This is a driver's bug!\n",
+                       active_links, n_links);
+               return -EINVAL;
+       }
+
+       source = found_link->source->entity;
+       for (i = 0; i < source->num_links; i++) {
+               struct media_entity *sink;
+               int flags = 0;
+
+               link = &source->links[i];
+               sink = link->sink->entity;
+
+               if (sink == entity)
+                       flags = MEDIA_LNK_FL_ENABLED;
+
+               ret = media_entity_setup_link(link, flags);
+               if (ret) {
+                       dev_err(fe->dvb->device,
+                               "Couldn't change link %s->%s to %s. Error %d\n",
+                               source->name, sink->name,
+                               flags ? "enabled" : "disabled",
+                               ret);
+                       return ret;
+               } else
+                       dev_dbg(fe->dvb->device,
+                               "link %s->%s was %s\n",
+                               source->name, sink->name,
+                               flags ? "ENABLED" : "disabled");
+       }
+#endif
+       return 0;
+}
+
 static int dvb_frontend_thread(void *data)
 {
        struct dvb_frontend *fe = data;
        struct dvb_frontend_private *fepriv = fe->frontend_priv;
        fe_status_t s;
        enum dvbfe_algo algo;
+       int ret;
 
        bool re_tune = false;
        bool semheld = false;
@@ -609,6 +696,13 @@ static int dvb_frontend_thread(void *data)
        fepriv->wakeup = 0;
        fepriv->reinitialise = 0;
 
+       ret = dvb_enable_media_tuner(fe);
+       if (ret) {
+               /* FIXME: return an error if it fails */
+               dev_info(fe->dvb->device,
+                       "proceeding with FE task\n");
+       }
+
        dvb_frontend_init(fe);
 
        set_freezable();
-- 
2.1.0

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