[PATCH 1/2 v3] ALSA: Add snd_ctl_update() to dynamically update a control

[Dimitris Papastamos <dp@opensource.wolfsonmicro.com>]

Add a function to dynamically update 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 update existing controls.
A separate patch needs to be made to allow ALSA Mixer to update the
controls dynamically.

Signed-off-by: Dimitris Papastamos <dp@opensource.wolfsonmicro.com>
---
 Hi,

 Any potentially locking related issues have been fixed now.
 Any comments on whether it would be advisable to use the same `numid' when
 I update an existing control?

 Thanks,
 Dimitris

 include/sound/control.h |    1 +
 sound/core/control.c    |   65 +++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 66 insertions(+), 0 deletions(-)

diff --git a/include/sound/control.h b/include/sound/control.h
index e67db28..2a2fd82 100644
--- a/include/sound/control.h
+++ b/include/sound/control.h
@@ -113,6 +113,7 @@ struct snd_kcontrol *snd_ctl_new1(const struct snd_kcontrol_new * kcontrolnew, v
 void snd_ctl_free_one(struct snd_kcontrol * kcontrol);
 int snd_ctl_add(struct snd_card * card, struct snd_kcontrol * kcontrol);
 int snd_ctl_remove(struct snd_card * card, struct snd_kcontrol * kcontrol);
+int snd_ctl_update(struct snd_card * card, struct snd_kcontrol * kcontrol, bool add_on_update);
 int snd_ctl_remove_id(struct snd_card * card, struct snd_ctl_elem_id *id);
 int snd_ctl_rename_id(struct snd_card * card, struct snd_ctl_elem_id *src_id, struct snd_ctl_elem_id *dst_id);
 int snd_ctl_activate_id(struct snd_card *card, struct snd_ctl_elem_id *id,
diff --git a/sound/core/control.c b/sound/core/control.c
index db51e4e..1d2b524 100644
--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -368,6 +368,71 @@ int snd_ctl_add(struct snd_card *card, struct snd_kcontrol *kcontrol)
 EXPORT_SYMBOL(snd_ctl_add);
 
 /**
+ * snd_ctl_update - update the control instance of the card
+ * @card: the card instance
+ * @kcontrol: the control instance to update
+ * @add_on_update: add the control if not already added
+ *
+ * Updates the given control.  If the given control does not exist
+ * and the add_on_update 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 updated.
+ */
+int snd_ctl_update(struct snd_card *card, struct snd_kcontrol *kcontrol,
+		   bool add_on_update)
+{
+	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_update)
+			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_update);
+
+/**
  * snd_ctl_remove - remove the control from the card and release it
  * @card: the card instance
  * @kcontrol: the control instance to remove
-- 
1.7.4.1