firewire: fw-sbp2: try to increase reconnect_hold (speed up reconnection)

Ask the target to grant 4 seconds instead of the standard and minimum of
1 second window after bus reset for reconnection.  This accelerates
reconnection if there are more than one targets on the bus:  If a login
and inquiry to one target blocks the fw-sbp2 workqueue for more than 1s
after bus reset, we now still can reconnect to the other target.

Before that, fw-sbp2's reconnect attempts would be rejected with "error
status: 0:9" (function rejected), and fw-sbp2 would finally re-login.
All those futile reconnect attemps cost extra time until the target
which needs re-login is ready for I/O again.

The reconnect timeout field in the login ORB doesn't have to be honored
by the target though.  I found that we could get up to
  - allegedly 32768s from an old OXFW911 firmware
  - 256s from LSI bridges
  - 4s from OXUF922 and OXFW912 bridges,
  - 2s from TI bridges,
  - only the standard 1s from Initio and Prolific bridges and from
    Apple OpenFirmware in target mode.

We just try to get 4 seconds which already covers the case of a few
HDDs on the same bus quite nicely.

A minor drawback occurs in the following (rare and impractical) border
case:
  - two initiators are there, initiator 1 holds an exclusive login to
    a target,
  - initiator 1 goes off the bus,
  - target refuses login attempts from initiator 2 until reconnect_hold
    seconds after bus reset.

An alternative approach to the issue at hand would be to parallelize
fw-sbp2's reconnect and login work.
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Acked-by: Jarod Wilson <jwilson@redhat.com>

drivers/firewire/fw-sbp2.c

@@ -514,9 +514,10 @@ sbp2_send_management_orb(struct sbp2_logical_unit *lu, int node_id,
 	orb->request.status_fifo.low  = lu->address_handler.offset;
 
 	if (function == SBP2_LOGIN_REQUEST) {
+		/* Ask for 2^2 == 4 seconds reconnect grace period */
 		orb->request.misc |=
-			MANAGEMENT_ORB_EXCLUSIVE(sbp2_param_exclusive_login) |
-			MANAGEMENT_ORB_RECONNECT(0);
+			MANAGEMENT_ORB_RECONNECT(2) |
+			MANAGEMENT_ORB_EXCLUSIVE(sbp2_param_exclusive_login);
 	}
 
 	fw_memcpy_to_be32(&orb->request, &orb->request, sizeof(orb->request));