Mute ALSA audio completely

chrome/browser/chromeos/audio_mixer_alsa.cc

 // Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/chromeos/audio_mixer_alsa.h"
 
 #include <cmath>
 
 #include <alsa/asoundlib.h>
 
@@ skipping 157 matching lines @@
   if (old_value != mute) {
     if (mute) {
       save_volume_ = DoGetVolumeDb_Locked();
       DoSetVolumeDb_Locked(min_volume_);
     } else {
       DoSetVolumeDb_Locked(save_volume_);
     }
   }
 
   SetElementMuted_Locked(elem_master_, mute);
-  if (elem_pcm_)
-    SetElementMuted_Locked(elem_pcm_, mute);

[davejcool, 2011/03/03 20:05:02]

It turns out the PCM mixer element does have a mute control and does not need to
be muted as well.  Before this change CL, the PCM element was not even being
found, so this was not noticed.

   prefs_->SetInteger(prefs::kAudioMute, mute ? kPrefMuteOn : kPrefMuteOff);
 }
 
 AudioMixer::State AudioMixerAlsa::GetState() const {
   base::AutoLock lock(mixer_state_lock_);
   // If we think it's ready, verify it is actually so.
   if ((mixer_state_ == READY) && (alsa_mixer_ == NULL))
     mixer_state_ = IN_ERROR;
   return mixer_state_;
 }
@@ skipping 49 matching lines @@
 
 bool AudioMixerAlsa::InitializeAlsaMixer() {
   base::AutoLock lock(mixer_state_lock_);
   if (mixer_state_ != INITIALIZING)
     return false;
 
   int err;
   snd_mixer_t* handle = NULL;
   const char* card = "default";
 
+  // Verify PCM can be opened, which also instantiates the PCM mixer element
+  // which is needed for finer volume control and for muting by setting to zero.
+  // If it fails, we can still try to use the mixer as best we can.
+  snd_pcm_t* pcm_out_handle;
+  if ((err = snd_pcm_open(&pcm_out_handle,
+                          "default",
+                          SND_PCM_STREAM_PLAYBACK,
+                          0)) >= 0) {
+    snd_pcm_close(pcm_out_handle);
+  }
+  else
+  {
+    LOG(WARNING) << "ALSA PCM open: " << snd_strerror(err);
+  }
+
   if ((err = snd_mixer_open(&handle, 0)) < 0) {
     LOG(ERROR) << "ALSA mixer " << card << " open error: " << snd_strerror(err);
     return false;
   }
 
   if ((err = snd_mixer_attach(handle, card)) < 0) {
     LOG(ERROR) << "ALSA Attach to card " << card << " failed: "
                << snd_strerror(err);
     snd_mixer_close(handle);
     return false;
@@ skipping 82 matching lines @@
   VLOG(1) << "Setting volume to " << pref_volume << " and mute to " << mute;
 
   if (mute) {
     save_volume_ = pref_volume;
     DoSetVolumeDb_Locked(min_volume_);
   } else {
     DoSetVolumeDb_Locked(pref_volume);
   }
 
   SetElementMuted_Locked(elem_master_, mute);
-  if (elem_pcm_)
-    SetElementMuted_Locked(elem_pcm_, mute);
 }
 
 void AudioMixerAlsa::RestoreVolumeMuteOnUIThread() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
   // This happens during init, so set the volume off the UI thread.
   int mute = prefs_->GetInteger(prefs::kAudioMute);
   double vol = prefs_->GetDouble(prefs::kAudioVolume);
   {
     base::AutoLock lock(mixer_state_lock_);
     if (mixer_state_ == SHUTTING_DOWN)
@@ skipping 150 matching lines @@
   if (alsa_result != 0) {
     LOG(WARNING) << "snd_mixer_selem_set_playback_switch_all() failed: "
                  << snd_strerror(alsa_result);
   } else {
     VLOG(1) << "Set playback switch " << snd_mixer_selem_get_name(elem)
             << " to " << enabled;
   }
 }
 
 }  // namespace chromeos