firewire: remove incomplete Bus_Time CSR support

The current implementation of Bus_Time read access was buggy since it
did not ensure that Bus_Time.second_count_hi and second_count_lo came
from the same 128 seconds period.

Reported-by: Håkan Johansson <f96hajo@chalmers.se>

Instead of a fix, remove Bus_Time register support altogether.  The spec
requires all cycle master capable nodes to implement this (all Linux
nodes are cycle master capable) while it also says that it "may" be
initialized by the bus manager or by the IRM standing in for a bus
manager.  (Neither Linux' firewire-core nor ieee1394 nodemgr implement
this.)

Since we cannot rely on Bus_Time having been initialized by a bus
manager, it is better to return an error instead of a nonsensical value
on a read request to Bus_Time.

Alternatively, we could fix the Bus_Time read integrity bug _and_
implement (a) cycle master's write support of the register as well as
(b) bus manager's Bus_Time initialization service, i.e. preservation of
the Bus_Time when the cycle master node of a bus changes.  However, that
would be quite some code for a feature that is unreliable to begin with
and very likely unused in practice.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

1 files changed, 6 insertions, 11 deletions

diff --git a/drivers/firewire/core-transaction.c b/drivers/firewire/core-transaction.c
index 495849eb13cc..673b03f8b4ec 100644
--- a/drivers/firewire/core-transaction.c
+++ b/drivers/firewire/core-transaction.c
@@ -921,23 +921,15 @@ static void handle_registers(struct fw_card *card, struct fw_request *request,
 		void *payload, size_t length, void *callback_data)
 {
 	int reg = offset & ~CSR_REGISTER_BASE;
-	unsigned long long bus_time;
 	__be32 *data = payload;
 	int rcode = RCODE_COMPLETE;
 
 	switch (reg) {
 	case CSR_CYCLE_TIME:
-	case CSR_BUS_TIME:
-		if (!TCODE_IS_READ_REQUEST(tcode) || length != 4) {
-			rcode = RCODE_TYPE_ERROR;
-			break;
-		}
-
-		bus_time = card->driver->get_bus_time(card);
-		if (reg == CSR_CYCLE_TIME)
-			*data = cpu_to_be32(bus_time);
+		if (TCODE_IS_READ_REQUEST(tcode) && length == 4)
+			*data = cpu_to_be32(card->driver->get_cycle_time(card));
 		else
-			*data = cpu_to_be32(bus_time >> 25);
+			rcode = RCODE_TYPE_ERROR;
 		break;
 
 	case CSR_BROADCAST_CHANNEL:
@@ -968,6 +960,9 @@ static void handle_registers(struct fw_card *card, struct fw_request *request,
 	case CSR_BUSY_TIMEOUT:
 		/* FIXME: Implement this. */
 
+	case CSR_BUS_TIME:
+		/* Useless without initialization by the bus manager. */
+
 	default:
 		rcode = RCODE_ADDRESS_ERROR;
 		break;