ALSA: core: Add managed card creation

As a second step for preliminary to widen the devres usages among
sound drivers, this patch adds a new ALSA core API function,
snd_devm_card_new(), to create a snd_card object via devres.
When a card object is created by this new function, snd_card_free() is
called automatically and the card object resource gets released at the
device unbinding time.

However, the story isn't that simple.  A caveat is that we have to
call snd_card_free() at the very first of the whole resource release
procedure, in order to assure that the all exposed devices on
user-space are deleted and sync with processes accessing those devices
before releasing resources.

For achieving it, snd_card_register() adds a new devres action to
trigger snd_card_free() automatically when the given card object is a
"managed" one.  Since usually snd_card_register() is the last step of
the initialization, this should work in most cases.

With all these tricks, some drivers can get rid of the whole driver
remove callback code.

About a bit of implementation details: the patch adds two new flags to
snd_card object: managed and releasing.  The former indicates that the
object was created via snd_devm_card_new(), and the latter is used for
avoiding the double-free of snd_card_free() calls.  Both flags are
fairly internal and likely uninteresting to normal users.

Link: https://lore.kernel.org/r/20210715075941.23332-3-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/sound/core.h b/include/sound/core.h
index c4ade121727d..7885f903cd5a 100644
--- a/include/sound/core.h
+++ b/include/sound/core.h
@@ -117,6 +117,8 @@ struct snd_card {
 	struct device card_dev;		/* cardX object for sysfs */
 	const struct attribute_group *dev_groups[4]; /* assigned sysfs attr */
 	bool registered;		/* card_dev is registered? */
+	bool managed;			/* managed via devres */
+	bool releasing;			/* during card free process */
 	int sync_irq;			/* assigned irq, used for PCM sync */
 	wait_queue_head_t remove_sleep;
 
@@ -274,6 +276,9 @@ extern int (*snd_mixer_oss_notify_callback)(struct snd_card *card, int cmd);
 int snd_card_new(struct device *parent, int idx, const char *xid,
 		 struct module *module, int extra_size,
 		 struct snd_card **card_ret);
+int snd_devm_card_new(struct device *parent, int idx, const char *xid,
+		      struct module *module, size_t extra_size,
+		      struct snd_card **card_ret);
 
 int snd_card_disconnect(struct snd_card *card);
 void snd_card_disconnect_sync(struct snd_card *card);