firewire: core: check for 1394a compliant IRM, fix inaccessibility of Sony camcorder

Per IEEE 1394 clause 8.4.2.3, a contender for the IRM role shall check
whether the current IRM complies to 1394a-2000 or later.  If not force a
compliant node (e.g. itself) to become IRM.  This was implemented in the
older ieee1394 driver but not yet in firewire-core.

An older Sony camcorder (Sony DCR-TRV25) which implements 1394-1995 IRM
but neither 1394a-2000 IRM nor BM was now found to cause an
interoperability bug:
  - Camcorder becomes root node when plugged in, hence gets IRM role.
  - firewire-core successfully contends for BM role, proceeds to perform
    gap count optimization and resets the bus.
  - Sony camcorder ignores presence of a BM (against the spec, this is
    a firmware bug), performs its idea of gap count optimization and
    resets the bus.
  - Preceding two steps are repeated endlessly, bus never settles,
    regular I/O is practically impossible.
http://thread.gmane.org/gmane.linux.kernel.firewire.user/3913

This is an interoperability regression from the old to the new drivers.
Fix it indirectly by adding the 1394a IRM check.  The spec suggests
three and a half methods to determine 1394a compliance of a remote IRM;
we choose the method of testing the Config_ROM.Bus_Info.generation
field.  This is data that firewire-core should have readily available at
this point, i.e. does not require extra I/O.

Reported-by: Clemens Ladisch <clemens@ladisch.de> (missing 1394a check)
Reported-by: H. S. <hs.samix@gmail.com> (issue with Sony DCR-TRV25)
Tested-by: H. S. <hs.samix@gmail.com>

Cc: <stable@kernel.org> # .32.x and newer
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

drivers/firewire/core-card.c

@@ -231,7 +231,7 @@ void fw_schedule_bm_work(struct fw_card *card, unsigned long delay)
 static void fw_card_bm_work(struct work_struct *work)
 {
 	struct fw_card *card = container_of(work, struct fw_card, work.work);
-	struct fw_device *root_device;
+	struct fw_device *root_device, *irm_device;
 	struct fw_node *root_node;
 	unsigned long flags;
 	int root_id, new_root_id, irm_id, local_id;
@@ -239,6 +239,7 @@ static void fw_card_bm_work(struct work_struct *work)
 	bool do_reset = false;
 	bool root_device_is_running;
 	bool root_device_is_cmc;
+	bool irm_is_1394_1995_only;
 
 	spin_lock_irqsave(&card->lock, flags);
 
@@ -248,12 +249,18 @@ static void fw_card_bm_work(struct work_struct *work)
 	}
 
 	generation = card->generation;
+
 	root_node = card->root_node;
 	fw_node_get(root_node);
 	root_device = root_node->data;
 	root_device_is_running = root_device &&
 			atomic_read(&root_device->state) == FW_DEVICE_RUNNING;
 	root_device_is_cmc = root_device && root_device->cmc;
+
+	irm_device = card->irm_node->data;
+	irm_is_1394_1995_only = irm_device && irm_device->config_rom &&
+			(irm_device->config_rom[2] & 0x000000f0) == 0;
+
 	root_id  = root_node->node_id;
 	irm_id   = card->irm_node->node_id;
 	local_id = card->local_node->node_id;
@@ -276,8 +283,15 @@ static void fw_card_bm_work(struct work_struct *work)
 
 		if (!card->irm_node->link_on) {
 			new_root_id = local_id;
-			fw_notify("IRM has link off, making local node (%02x) root.\n",
-				  new_root_id);
+			fw_notify("%s, making local node (%02x) root.\n",
+				  "IRM has link off", new_root_id);
+			goto pick_me;
+		}
+
+		if (irm_is_1394_1995_only) {
+			new_root_id = local_id;
+			fw_notify("%s, making local node (%02x) root.\n",
+				  "IRM is not 1394a compliant", new_root_id);
 			goto pick_me;
 		}
 
@@ -316,8 +330,8 @@ static void fw_card_bm_work(struct work_struct *work)
 			 * root, and thus, IRM.
 			 */
 			new_root_id = local_id;
-			fw_notify("BM lock failed, making local node (%02x) root.\n",
-				  new_root_id);
+			fw_notify("%s, making local node (%02x) root.\n",
+				  "BM lock failed", new_root_id);
 			goto pick_me;
 		}
 	} else if (card->bm_generation != generation) {