1 files changed, 17 insertions, 1 deletions

diff --git a/drivers/firewire/core-device.c b/drivers/firewire/core-device.c
index d6e54a5173fc..97e656af2d22 100644
--- a/drivers/firewire/core-device.c
+++ b/drivers/firewire/core-device.c
@@ -580,7 +580,9 @@ static int read_bus_info_block(struct fw_device *device, int generation)
 
         kfree(old_rom);
         ret = 0;
-        device->cmc = rom[2] >> 30 & 1;
+        device->max_rec = rom[2] >> 12 & 0xf;
+        device->cmc     = rom[2] >> 30 & 1;
+        device->irmc    = rom[2] >> 31 & 1;
  out:
         kfree(rom);
 
@@ -841,6 +843,20 @@ static void set_broadcast_channel(struct fw_device *device, int generation)
         if (!card->broadcast_channel_allocated)
                 return;
 
+        /*
+         * The Broadcast_Channel Valid bit is required by nodes which want to
+         * transmit on this channel.  Such transmissions are practically
+         * exclusive to IP over 1394 (RFC 2734).  IP capable nodes are required
+         * to be IRM capable and have a max_rec of 8 or more.  We use this fact
+         * to narrow down to which nodes we send Broadcast_Channel updates.
+         */
+        if (!device->irmc || device->max_rec < 8)
+                return;
+
+        /*
+         * Some 1394-1995 nodes crash if this 1394a-2000 register is written.
+         * Perform a read test first.
+         */
         if (device->bc_implemented == BC_UNKNOWN) {
                 rcode = fw_run_transaction(card, TCODE_READ_QUADLET_REQUEST,
                                 device->node_id, generation, device->max_speed,