[PATCH 2/4] Introduce op_get_latency()

[Gregory P. <gre...@gm...>]

Output plugins may define .get_latency function in order to
communicate device latency back to cmus.

In case if output plugin does not define it, latency is assumed
to be 0.

Signed-off-by: Gregory Petrosyan <gre...@gm...>
---
 op.h     |    1 +
 output.c |   16 ++++++++++++++++
 output.h |    5 +++++
 3 files changed, 22 insertions(+), 0 deletions(-)

diff --git a/op.h b/op.h
index 5cca228..8b0d072 100644
--- a/op.h
+++ b/op.h
@@ -53,6 +53,7 @@ struct output_plugin_ops {
 	int (*buffer_space)(void);
 
 	/* these can be NULL */
+	int (*get_latency)(double *lat);
 	int (*pause)(void);
 	int (*unpause)(void);
 
diff --git a/output.c b/output.c
index cf15cfc..24aabb6 100644
--- a/output.c
+++ b/output.c
@@ -284,6 +284,22 @@ int op_buffer_space(void)
 	return rc;
 }
 
+int op_get_latency(double *lat)
+{
+	int rc;
+
+	if (op->pcm_ops->get_latency) {
+		rc = op->pcm_ops->get_latency(lat);
+		if (rc)
+			*lat = 0;
+	} else {
+		*lat = 0;
+		rc = OP_ERROR_SUCCESS;
+	}
+
+	return rc;
+}
+
 int mixer_set_volume(int left, int right)
 {
 	if (op == NULL)
diff --git a/output.h b/output.h
index 73bf241..4967772 100644
--- a/output.h
+++ b/output.h
@@ -64,6 +64,11 @@ int op_unpause(void);
 int op_buffer_space(void);
 
 /*
+ * *lat will contain output device latency in seconds
+ */
+int op_get_latency(double *lat);
+
+/*
  * errors: OP_ERROR_{}
  */
 int op_reset(void);
-- 
1.6.5