[PATCH v2 5/8] ALSA: add snd_ctl_add_locked()

[Oswald Buddenhagen <oswald.buddenhagen@xxxxxx>]

This is in fact more symmetrical to snd_ctl_remove() than snd_ctl_add()
is - the former could be named snd_ctl_remove_locked() just as well.

One may argue that this is going in the wrong direction, as drivers have
no business managing the lock. This may be true in principle, but in
practice the vast majority of controls is created even before the device
was registered, and therefore before any locking is necessary at all.
That means that an even more radical approach of changing snd_ctl_add()
do do no locking, and converting the call sites that actually need
locking to a new function, would better match reality, and would be
somewhat more efficient at that. However, that seems a bit risky and way
too much work.

This will be used to dynamically change the available controls from
another control's put() callback, which is already locked.

One might want to add snd_ctl_replace_locked() for completeness, but I
have no use for it now.

Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@xxxxxx>
---
v2:
- extended commit message
---
 include/sound/control.h |  1 +
 sound/core/control.c    | 31 +++++++++++++++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/include/sound/control.h b/include/sound/control.h
index cc3dcc6cfb0f..d4e210831a38 100644
--- a/include/sound/control.h
+++ b/include/sound/control.h
@@ -134,6 +134,7 @@ void snd_ctl_notify_one(struct snd_card * card, unsigned int mask, struct snd_kc
 struct snd_kcontrol *snd_ctl_new1(const struct snd_kcontrol_new * kcontrolnew, void * private_data);
 void snd_ctl_free_one(struct snd_kcontrol * kcontrol);
 int snd_ctl_add(struct snd_card * card, struct snd_kcontrol * kcontrol);
+int snd_ctl_add_locked(struct snd_card * card, struct snd_kcontrol * kcontrol);
 int snd_ctl_remove(struct snd_card * card, struct snd_kcontrol * kcontrol);
 int snd_ctl_replace(struct snd_card *card, struct snd_kcontrol *kcontrol, bool add_on_replace);
 int snd_ctl_remove_id(struct snd_card * card, struct snd_ctl_elem_id *id);
diff --git a/sound/core/control.c b/sound/core/control.c
index 82aa1af1d1d8..ede5ab911add 100644
--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -527,6 +527,27 @@ static int snd_ctl_add_replace(struct snd_card *card,
 	return err;
 }
 
+static int snd_ctl_add_replace_locked(struct snd_card *card,
+				      struct snd_kcontrol *kcontrol,
+				      enum snd_ctl_add_mode mode)
+{
+	int err = -EINVAL;
+
+	if (! kcontrol)
+		return err;
+	if (snd_BUG_ON(!card || !kcontrol->info))
+		goto error;
+
+	err = __snd_ctl_add_replace(card, kcontrol, mode);
+	if (err < 0)
+		goto error;
+	return 0;
+
+ error:
+	snd_ctl_free_one(kcontrol);
+	return err;
+}
+
 /**
  * snd_ctl_add - add the control instance to the card
  * @card: the card instance
@@ -547,6 +568,16 @@ int snd_ctl_add(struct snd_card *card, struct snd_kcontrol *kcontrol)
 }
 EXPORT_SYMBOL(snd_ctl_add);
 
+/**
+ * snd_ctl_add_locked - same as snd_ctl_add(), but card->controls_rwsem
+ * is expected to be already locked if necessary.
+ */
+int snd_ctl_add_locked(struct snd_card *card, struct snd_kcontrol *kcontrol)
+{
+	return snd_ctl_add_replace_locked(card, kcontrol, CTL_ADD_EXCLUSIVE);
+}
+EXPORT_SYMBOL(snd_ctl_add_locked);
+
 /**
  * snd_ctl_replace - replace the control instance of the card
  * @card: the card instance
-- 
2.40.0.152.g15d061e6df