Changes to the generic console support code that happened a while ago
introduced a scenario where the initial console is used in parallel with
the final console during a brief period when switching between the two is
in progress. During that time a message about the switch-over is printed.
With some combinations of chips, firmware and drivers, such as the DEC
DZ11 clone used with the DECstation, a hang may happen because the
firmware used for the initial console may not expect the state of the chip
after it has been initialised by the driver.
This is a workaround for the DZ11 which reuses the power-management
callback to keep the transmitter of the line associated with the console
enabled. It reflects the consensus reached in a discussion a while ago.
Signed-off-by: Maciej W. Rozycki <macro@xxxxxxxxxxxxxx>
---
patch-mips-2.6.23-rc5-20070904-dz-pm-1
diff -up --recursive --new-file linux-mips-2.6.23-rc5-20070904.macro/drivers/serial/dz.c linux-mips-2.6.23-rc5-20070904/drivers/serial/dz.c
--- linux-mips-2.6.23-rc5-20070904.macro/drivers/serial/dz.c 2007-10-14 00:49:58.000000000 +0000
+++ linux-mips-2.6.23-rc5-20070904/drivers/serial/dz.c 2007-10-14 01:46:41.000000000 +0000
@@ -637,6 +637,26 @@ static void dz_set_termios(struct uart_p
spin_unlock_irqrestore(&dport->port.lock, flags);
}
+/*
+ * Hack alert!
+ * Required solely so that the initial PROM-based console
+ * works undisturbed in parallel with this one.
+ */
+static void dz_pm(struct uart_port *uport, unsigned int state,
+ unsigned int oldstate)
+{
+ struct dz_port *dport = to_dport(uport);
+ unsigned long flags;
+
+ spin_lock_irqsave(&dport->port.lock, flags);
+ if (state < 3)
+ dz_start_tx(&dport->port);
+ else
+ dz_stop_tx(&dport->port);
+ spin_unlock_irqrestore(&dport->port.lock, flags);
+}
+
+
static const char *dz_type(struct uart_port *uport)
{
return "DZ";
@@ -733,6 +753,7 @@ static struct uart_ops dz_ops = {
.startup = dz_startup,
.shutdown = dz_shutdown,
.set_termios = dz_set_termios,
+ .pm = dz_pm,
.type = dz_type,
.release_port = dz_release_port,
.request_port = dz_request_port,
@@ -856,7 +877,10 @@ static int __init dz_console_setup(struc
if (ret)
return ret;
+ spin_lock_init(&dport->port.lock); /* For dz_pm(). */
+
dz_reset(dport);
+ dz_pm(uport, 0, -1);
if (options)
uart_parse_options(options, &baud, &parity, &bits, &flow);
