firewire: fix use of multiple AV/C devices, allow multiple FCP listeners

Control of more than one AV/C device at once --- e.g. camcorders, tape
decks, audio devices, TV tuners --- failed or worked only unreliably,
depending on driver implementation.  This affected kernelspace and
userspace drivers alike and was caused by firewire-core's inability to
accept multiple registrations of FCP listeners.

The fix allows multiple address handlers to be registered for the FCP
command and response registers.  When a request for these registers is
received, all handlers are invoked, and the Firewire response is
generated by the core and not by any handler.

The cdev API does not change, i.e., userspace is still expected to send
a response for FCP requests; this response is silently ignored.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de> (changelog, rebased, whitespace)

1 files changed, 2 insertions, 2 deletions

diff --git a/include/linux/firewire.h b/include/linux/firewire.h
index 9416a461b696..a0e67150a729 100644
--- a/include/linux/firewire.h
+++ b/include/linux/firewire.h
@@ -248,8 +248,8 @@ typedef void (*fw_transaction_callback_t)(struct fw_card *card, int rcode,
                                           void *data, size_t length,
                                           void *callback_data);
 /*
- * Important note:  The callback must guarantee that either fw_send_response()
- * or kfree() is called on the @request.
+ * Important note:  Except for the FCP registers, the callback must guarantee
+ * that either fw_send_response() or kfree() is called on the @request.
  */
 typedef void (*fw_address_callback_t)(struct fw_card *card,
                                       struct fw_request *request,