ALSA: Add snd_ctl_replace() to dynamically replace a control

Add a function to dynamically replace a given control.  If the
control does not already exist, a third parameter is used to determine
whether to actually add that control.  This is useful in cases where
downloadable firmware at runtime can add or replace existing controls.
A separate patch needs to be made to allow ALSA Mixer to render the
replaced controls on the fly.

Signed-off-by: Dimitris Papastamos <dp@opensource.wolfsonmicro.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 64 insertions, 0 deletions

diff --git a/sound/core/control.c b/sound/core/control.c
index a08ad57c49b6..5d98194bcad5 100644
--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -366,6 +366,70 @@ int snd_ctl_add(struct snd_card *card, struct snd_kcontrol *kcontrol)
 EXPORT_SYMBOL(snd_ctl_add);
 
 /**
+ * snd_ctl_replace - replace the control instance of the card
+ * @card: the card instance
+ * @kcontrol: the control instance to replace
+ * @add_on_replace: add the control if not already added
+ *
+ * Replaces the given control.  If the given control does not exist
+ * and the add_on_replace flag is set, the control is added.  If the
+ * control exists, it is destroyed first.
+ *
+ * Returns zero if successful, or a negative error code on failure.
+ *
+ * It frees automatically the control which cannot be added or replaced.
+ */
+int snd_ctl_replace(struct snd_card *card, struct snd_kcontrol *kcontrol,
+                    bool add_on_replace)
+{
+        struct snd_ctl_elem_id id;
+        unsigned int idx;
+        struct snd_kcontrol *old;
+        int ret;
+
+        if (!kcontrol)
+                return -EINVAL;
+        if (snd_BUG_ON(!card || !kcontrol->info)) {
+                ret = -EINVAL;
+                goto error;
+        }
+        id = kcontrol->id;
+        down_write(&card->controls_rwsem);
+        old = snd_ctl_find_id(card, &id);
+        if (!old) {
+                if (add_on_replace)
+                        goto add;
+                up_write(&card->controls_rwsem);
+                ret = -EINVAL;
+                goto error;
+        }
+        ret = snd_ctl_remove(card, old);
+        if (ret < 0) {
+                up_write(&card->controls_rwsem);
+                goto error;
+        }
+add:
+        if (snd_ctl_find_hole(card, kcontrol->count) < 0) {
+                up_write(&card->controls_rwsem);
+                ret = -ENOMEM;
+                goto error;
+        }
+        list_add_tail(&kcontrol->list, &card->controls);
+        card->controls_count += kcontrol->count;
+        kcontrol->id.numid = card->last_numid + 1;
+        card->last_numid += kcontrol->count;
+        up_write(&card->controls_rwsem);
+        for (idx = 0; idx < kcontrol->count; idx++, id.index++, id.numid++)
+                snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_ADD, &id);
+        return 0;
+
+error:
+        snd_ctl_free_one(kcontrol);
+        return ret;
+}
+EXPORT_SYMBOL(snd_ctl_replace);
+
+/**
  * snd_ctl_remove - remove the control from the card and release it
  * @card: the card instance
  * @kcontrol: the control instance to remove