ALSA: hda - Add / fix comments about capture vol/sw controls in hda_generic.c

A bit of details won't hurt.

Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/pci/hda/hda_generic.c b/sound/pci/hda/hda_generic.c
index 3e818b6..f5eb57c 100644 (file)
--- a/sound/pci/hda/hda_generic.c
+++ b/sound/pci/hda/hda_generic.c
@@ -1877,10 +1877,6 @@ static int mux_enum_put(struct snd_kcontrol *kcontrol,
                          ucontrol->value.enumerated.item[0]);
 }
 
-/*
- * capture volume and capture switch ctls
- */
-
 static const struct snd_kcontrol_new cap_src_temp = {
        .iface = SNDRV_CTL_ELEM_IFACE_MIXER,
        .name = "Input Source",
@@ -1889,9 +1885,14 @@ static const struct snd_kcontrol_new cap_src_temp = {
        .put = mux_enum_put,
 };
 
+/*
+ * capture volume and capture switch ctls
+ */
+
 typedef int (*put_call_t)(struct snd_kcontrol *kcontrol,
                          struct snd_ctl_elem_value *ucontrol);
 
+/* call the given amp update function for all amps in the imux list at once */
 static int cap_put_caller(struct snd_kcontrol *kcontrol,
                          struct snd_ctl_elem_value *ucontrol,
                          put_call_t func, int type)
@@ -1905,6 +1906,10 @@ static int cap_put_caller(struct snd_kcontrol *kcontrol,
        imux = &spec->input_mux;
        adc_idx = snd_ctl_get_ioffidx(kcontrol, &ucontrol->id);
        mutex_lock(&codec->control_mutex);
+       /* we use the cache-only update at first since multiple input paths
+        * may shared the same amp; by updating only caches, the redundant
+        * writes to hardware can be reduced.
+        */
        codec->cached_write = 1;
        for (i = 0; i < imux->num_items; i++) {
                path = snd_hda_get_nid_path(codec, spec->imux_pins[i],
@@ -1919,7 +1924,7 @@ static int cap_put_caller(struct snd_kcontrol *kcontrol,
  error:
        codec->cached_write = 0;
        mutex_unlock(&codec->control_mutex);
-       snd_hda_codec_flush_amp_cache(codec);
+       snd_hda_codec_flush_amp_cache(codec); /* flush the updates */
        if (err >= 0 && spec->cap_sync_hook)
                spec->cap_sync_hook(codec);
        return err;