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>

diff --git a/include/sound/core.h b/include/sound/core.h
index c4ade12..7885f90 100644 (file)
--- 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);

diff --git a/sound/core/init.c b/sound/core/init.c
index 1490568..e985185 100644 (file)
--- a/sound/core/init.c
+++ b/sound/core/init.c
@@ -134,6 +134,9 @@ void snd_device_initialize(struct device *dev, struct snd_card *card)
 }
 EXPORT_SYMBOL_GPL(snd_device_initialize);
 
+static int snd_card_init(struct snd_card *card, struct device *parent,
+                        int idx, const char *xid, struct module *module,
+                        size_t extra_size);
 static int snd_card_do_free(struct snd_card *card);
 static const struct attribute_group card_dev_attr_group;
 
@@ -163,9 +166,6 @@ int snd_card_new(struct device *parent, int idx, const char *xid,
 {
        struct snd_card *card;
        int err;
-#ifdef CONFIG_SND_DEBUG
-       char name[8];
-#endif
 
        if (snd_BUG_ON(!card_ret))
                return -EINVAL;
@@ -176,6 +176,74 @@ int snd_card_new(struct device *parent, int idx, const char *xid,
        card = kzalloc(sizeof(*card) + extra_size, GFP_KERNEL);
        if (!card)
                return -ENOMEM;
+
+       err = snd_card_init(card, parent, idx, xid, module, extra_size);
+       if (err < 0) {
+               kfree(card);
+               return err;
+       }
+
+       *card_ret = card;
+       return 0;
+}
+EXPORT_SYMBOL(snd_card_new);
+
+static void __snd_card_release(struct device *dev, void *data)
+{
+       snd_card_free(data);
+}
+
+/**
+ * snd_devm_card_new - managed snd_card object creation
+ * @parent: the parent device object
+ * @idx: card index (address) [0 ... (SNDRV_CARDS-1)]
+ * @xid: card identification (ASCII string)
+ * @module: top level module for locking
+ * @extra_size: allocate this extra size after the main soundcard structure
+ * @card_ret: the pointer to store the created card instance
+ *
+ * This function works like snd_card_new() but manages the allocated resource
+ * via devres, i.e. you don't need to free explicitly.
+ *
+ * When a snd_card object is created with this function and registered via
+ * snd_card_register(), the very first devres action to call snd_card_free()
+ * is added automatically.  In that way, the resource disconnection is assured
+ * at first, then released in the expected order.
+ */
+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)
+{
+       struct snd_card *card;
+       int err;
+
+       *card_ret = NULL;
+       card = devres_alloc(__snd_card_release, sizeof(*card) + extra_size,
+                           GFP_KERNEL);
+       if (!card)
+               return -ENOMEM;
+       card->managed = true;
+       err = snd_card_init(card, parent, idx, xid, module, extra_size);
+       if (err < 0) {
+               devres_free(card);
+               return err;
+       }
+
+       devres_add(parent, card);
+       *card_ret = card;
+       return 0;
+}
+EXPORT_SYMBOL_GPL(snd_devm_card_new);
+
+static int snd_card_init(struct snd_card *card, struct device *parent,
+                        int idx, const char *xid, struct module *module,
+                        size_t extra_size)
+{
+       int err;
+#ifdef CONFIG_SND_DEBUG
+       char name[8];
+#endif
+
        if (extra_size > 0)
                card->private_data = (char *)card + sizeof(struct snd_card);
        if (xid)
@@ -197,7 +265,6 @@ int snd_card_new(struct device *parent, int idx, const char *xid,
                mutex_unlock(&snd_card_mutex);
                dev_err(parent, "cannot find the slot for index %d (range 0-%i), error: %d\n",
                         idx, snd_ecards_limit - 1, err);
-               kfree(card);
                return err;
        }
        set_bit(idx, snd_cards_lock);           /* lock it */
@@ -256,8 +323,6 @@ int snd_card_new(struct device *parent, int idx, const char *xid,
        sprintf(name, "card%d", idx);
        card->debugfs_root = debugfs_create_dir(name, sound_debugfs_root);
 #endif
-
-       *card_ret = card;
        return 0;
 
       __error_ctl:
@@ -266,7 +331,6 @@ int snd_card_new(struct device *parent, int idx, const char *xid,
        put_device(&card->card_dev);
        return err;
 }
-EXPORT_SYMBOL(snd_card_new);
 
 /**
  * snd_card_ref - Get the card object from the index
@@ -481,6 +545,7 @@ EXPORT_SYMBOL_GPL(snd_card_disconnect_sync);
 
 static int snd_card_do_free(struct snd_card *card)
 {
+       card->releasing = true;
 #if IS_ENABLED(CONFIG_SND_MIXER_OSS)
        if (snd_mixer_oss_notify_callback)
                snd_mixer_oss_notify_callback(card, SND_MIXER_OSS_NOTIFY_FREE);
@@ -498,7 +563,8 @@ static int snd_card_do_free(struct snd_card *card)
 #endif
        if (card->release_completion)
                complete(card->release_completion);
-       kfree(card);
+       if (!card->managed)
+               kfree(card);
        return 0;
 }
 
@@ -745,6 +811,14 @@ int snd_card_add_dev_attr(struct snd_card *card,
 }
 EXPORT_SYMBOL_GPL(snd_card_add_dev_attr);
 
+static void trigger_card_free(void *data)
+{
+       struct snd_card *card = data;
+
+       if (!card->releasing)
+               snd_card_free(data);
+}
+
 /**
  *  snd_card_register - register the soundcard
  *  @card: soundcard structure
@@ -768,6 +842,15 @@ int snd_card_register(struct snd_card *card)
                if (err < 0)
                        return err;
                card->registered = true;
+       } else {
+               if (card->managed)
+                       devm_remove_action(card->dev, trigger_card_free, card);
+       }
+
+       if (card->managed) {
+               err = devm_add_action(card->dev, trigger_card_free, card);
+               if (err < 0)
+                       return err;
        }
 
        err = snd_device_register_all(card);