mixer: add support for pcm device specific mixer controls

Mixer control such as "Playback channel map" can be registered by
multiple pcm device nodes and is distinguished by device in
snd_ctl_elem_id. Add support to get the control handle associated
with mixer ctl name and device number.
Also, introduce API to get the device number associated with specific
mixer_ctl handle.

1 files changed, 57 insertions, 0 deletions

diff --git a/src/mixer.c b/src/mixer.c
index 029fc84..f2c21c3 100644
--- a/src/mixer.c
+++ b/src/mixer.c
@@ -760,6 +760,55 @@ struct mixer_ctl *mixer_get_ctl_by_name_and_index(struct mixer *mixer,
     return NULL;
 }
 
+/** Gets an instance of mixer control handle, by the mixer control's name and device.
+ *  For instance, if two controls have same name,
+ *  e.g. 'Playback Channel map', then PCM device returns the specific control.
+ * @param mixer An initialized mixer handle.
+ * @param name The control's name in the given mixer.
+ * @param device The PCM device
+ * @returns A handle to the mixer control.
+ * @ingroup libtinyalsa-mixer
+ */
+struct mixer_ctl *mixer_get_ctl_by_name_and_device(struct mixer *mixer,
+                                                   const char *name,
+                                                   unsigned int device)
+{
+    struct mixer_ctl_group *grp;
+    unsigned int n;
+    struct mixer_ctl *ctl;
+
+    if (!mixer || !name) {
+        return NULL;
+    }
+
+    if (mixer->h_grp) {
+        grp = mixer->h_grp;
+        ctl = grp->ctl;
+
+        for (n = 0; n < grp->count; n++) {
+            if (!strcmp(name, (char*) ctl[n].info.id.name) &&
+                    device == ctl[n].info.id.device) {
+                return ctl + n;
+            }
+        }
+    }
+
+#ifdef TINYALSA_USES_PLUGINS
+    if (mixer->v_grp) {
+        grp = mixer->v_grp;
+        ctl = grp->ctl;
+
+        for (n = 0; n < grp->count; n++) {
+            if (!strcmp(name, (char*) ctl[n].info.id.name) &&
+                    device == ctl[n].info.id.device) {
+                return ctl + n;
+            }
+        }
+    }
+#endif
+    return NULL;
+}
+
 /** Updates the control's info.
  * This is useful for a program that may be idle for a period of time.
  * @param ctl An initialized control handle.
@@ -822,6 +871,14 @@ const char *mixer_ctl_get_name(const struct mixer_ctl *ctl)
     return (const char *)ctl->info.id.name;
 }
 
+unsigned int mixer_ctl_get_device(const struct mixer_ctl *ctl)
+{
+    if (!ctl)
+        return UINT_MAX;
+
+    return ctl->info.id.device;
+}
+
 /** Gets the value type of the control.
  * @param ctl An initialized control handle
  * @returns On success, the type of mixer control.