Rework hardware probing and RTL-SDR helper startup

The lazy startup of the separate helper program for the RTL-SDR
backend on playback start was incorrect with respect to the expected
behavior the frequency setting verbs.  This was not visible during
usage by the radio application, but was triggering failures in
several tests in the pyagl binding wrapper test suite.  To facilitate
starting the helper during backend initialization, the probing part
of the backend "init" has been split into a separate "probe" function,
and all backends have been updated to reflect this change.  Logic has
been added to enforce that "init" is only called after "probe" has
succeeded for a backend, and a comment has been added to radio_impl.h
to document this intended behavior.

Bug-AGL: SPEC-3717

Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: Ic37331a92bae7cc01ee448e69894fa5f49d08a74

1 files changed, 19 insertions, 14 deletions

diff --git a/binding/radio-binding.c b/binding/radio-binding.c
index 3b8561d..8b5559c 100644
--- a/binding/radio-binding.c
+++ b/binding/radio-binding.c
@@ -678,36 +678,41 @@ static void onevent(afb_api_t api, const char *event, struct json_object *object
 
 static int init(afb_api_t api)
 {
-	// Look for RTL-SDR USB adapter
+	// Probe for radio backends
 	radio_impl_ops = &rtlsdr_impl_ops;
-	int rc = radio_impl_ops->init();
+	int rc = radio_impl_ops->probe();
 	if(rc != 0) {
 		// Look for Kingfisher Si4689
 		radio_impl_ops = &kf_impl_ops;
-		rc = radio_impl_ops->init();
+		rc = radio_impl_ops->probe();
 	}
 	if(rc != 0) {
 		radio_impl_ops = &tef665x_impl_ops;
-		rc = radio_impl_ops->init();
+		rc = radio_impl_ops->probe();
 	}
 	if (rc != 0) {
 		radio_impl_ops = &null_impl_ops;
-		rc = radio_impl_ops->init();
+		rc = radio_impl_ops->probe();
 	}
 	if (rc != 0) {
-		// We don't expect the null implementation to fail init, but just in case...
+		// We don't expect the null implementation to fail probe, but just in case...
 		AFB_API_ERROR(afbBindingV3root, "No radio device found, exiting");
+		return rc;
 	}
-	if(rc == 0) {
-		AFB_API_NOTICE(afbBindingV3root, "%s found\n", radio_impl_ops->name);
-		radio_impl_ops->set_frequency_callback(freq_callback, NULL);
-		if(radio_impl_ops->set_rds_callback)
-		{
-			radio_impl_ops->set_rds_callback(rds_callback);
-		}
-	} else {
+	// Try to initialize detected backend
+	rc = radio_impl_ops->init();
+	if(rc < 0) {
+		AFB_API_ERROR(afbBindingV3root,
+			      "%s initialization failed\n",
+			      radio_impl_ops->name);
 		return rc;
 	}
+	AFB_API_NOTICE(afbBindingV3root, "%s found\n", radio_impl_ops->name);
+	radio_impl_ops->set_frequency_callback(freq_callback, NULL);
+	radio_impl_ops->set_frequency_callback(freq_callback, NULL);
+	if(radio_impl_ops->set_rds_callback) {
+		radio_impl_ops->set_rds_callback(rds_callback);
+	}
 
 	rc = afb_daemon_require_api("signal-composer", 1);
 	if (rc) {