alsa: add host suspend/resume support

Both input and output streams may be in SND_PCM_STATE_SUSPENDED
after the host is suspended and resumed, meaning "Hardware is
suspended".  snd_pcm_readi() and snd_pcm_writei() will return
-ESTRPIPE if called while the stream is in this state.

Call snd_pcm_resume() to enable audio output and capture after
host resume.

Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: malc <av1474@comtv.ru>

audio/alsaaudio.c

@@ -503,6 +503,16 @@ static int alsa_recover (snd_pcm_t *handle)
     return 0;
 }
 
+static int alsa_resume (snd_pcm_t *handle)
+{
+    int err = snd_pcm_resume (handle);
+    if (err < 0) {
+        alsa_logerr (err, "Failed to resume handle %p\n", handle);
+        return -1;
+    }
+    return 0;
+}
+
 static snd_pcm_sframes_t alsa_get_avail (snd_pcm_t *handle)
 {
     snd_pcm_sframes_t avail;
@@ -580,6 +590,19 @@ static int alsa_run_out (HWVoiceOut *hw)
                     }
                     continue;
 
+                case -ESTRPIPE:
+                    /* stream is suspended and waiting for an
+                       application recovery */
+                    if (alsa_resume (alsa->handle)) {
+                        alsa_logerr (written, "Failed to write %d frames\n",
+                                     len);
+                        goto exit;
+                    }
+                    if (conf.verbose) {
+                        dolog ("Resuming suspended output stream\n");
+                    }
+                    continue;
+
                 case -EAGAIN:
                     goto exit;
 
@@ -779,8 +802,30 @@ static int alsa_run_in (HWVoiceIn *hw)
         return 0;
     }
 
-    if (!avail && (snd_pcm_state (alsa->handle) == SND_PCM_STATE_PREPARED)) {
+    if (!avail) {
-        avail = hw->samples;
+        snd_pcm_state_t state;
+
+        state = snd_pcm_state (alsa->handle);
+        switch (state) {
+        case SND_PCM_STATE_PREPARED:
+            avail = hw->samples;
+            break;
+        case SND_PCM_STATE_SUSPENDED:
+            /* stream is suspended and waiting for an application recovery */
+            if (alsa_resume (alsa->handle)) {
+                dolog ("Failed to resume suspended input stream\n");
+                return 0;
+            }
+            if (conf.verbose) {
+                dolog ("Resuming suspended input stream\n");
+            }
+            break;
+        default:
+            if (conf.verbose) {
+                dolog ("No frames available and ALSA state is %d\n", state);
+            }
+            return 0;
+        }
     }
 
     decr = audio_MIN (dead, avail);