ALSA: firewire/bebob: Add a workaround for M-Audio special Firewire series

In post commit, a quirk of this firmware about transactions is reported.
This commit apply a workaround for this quirk.

They often fail transactions due to gap_count mismatch. This state is changed
by generating bus reset.

The fw_schedule_bus_reset() is an exported symbol in firewire-core. But there
are no header for public. This commit moves its prototype from
drivers/firewire/core.h to include/linux/firewire.h.

This mismatch still affects bus management before generating this bus reset.
It still takes a time to call driver's probe() because transactions are still
often failed.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

2 files changed, 29 insertions, 4 deletions

diff --git a/sound/firewire/bebob/bebob.c b/sound/firewire/bebob/bebob.c
index e1dd4219ea6c..31b96b7264cf 100644
--- a/sound/firewire/bebob/bebob.c
+++ b/sound/firewire/bebob/bebob.c
@@ -247,10 +247,26 @@ bebob_probe(struct fw_unit *unit,
         if (err < 0)
                 goto error;
 
-        err = snd_card_register(card);
-        if (err < 0) {
-                snd_bebob_stream_destroy_duplex(bebob);
-                goto error;
+        if (!bebob->maudio_special_quirk) {
+                err = snd_card_register(card);
+                if (err < 0) {
+                        snd_bebob_stream_destroy_duplex(bebob);
+                        goto error;
+                }
+        } else {
+                /*
+                 * This is a workaround. This bus reset seems to have an effect
+                 * to make devices correctly handling transactions. Without
+                 * this, the devices have gap_count mismatch. This causes much
+                 * failure of transaction.
+                 *
+                 * Just after registration, user-land application receive
+                 * signals from dbus and starts I/Os. To avoid I/Os till the
+                 * future bus reset, registration is done in next update().
+                 */
+                bebob->deferred_registration = true;
+                fw_schedule_bus_reset(fw_parent_device(bebob->unit)->card,
+                                      false, true);
         }
 
         dev_set_drvdata(&unit->device, bebob);
@@ -273,6 +289,14 @@ bebob_update(struct fw_unit *unit)
 
         fcp_bus_reset(bebob->unit);
         snd_bebob_stream_update_duplex(bebob);
+
+        if (bebob->deferred_registration) {
+                if (snd_card_register(bebob->card) < 0) {
+                        snd_bebob_stream_destroy_duplex(bebob);
+                        snd_card_free(bebob->card);
+                }
+                bebob->deferred_registration = false;
+        }
 }
 
 static void bebob_remove(struct fw_unit *unit)
diff --git a/sound/firewire/bebob/bebob.h b/sound/firewire/bebob/bebob.h
index 4a54e746c5c6..91b26b0c649a 100644
--- a/sound/firewire/bebob/bebob.h
+++ b/sound/firewire/bebob/bebob.h
@@ -109,6 +109,7 @@ struct snd_bebob {
 
         /* for M-Audio special devices */
         void *maudio_special_quirk;
+        bool deferred_registration;
 };
 
 static inline int