serial: DZ11: avoid a hang at console switch-over
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@linux-mips.org>
Cc: Jiri Slaby <jirislaby@gmail.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/serial/dz.c b/drivers/serial/dz.c
index a81d2c2..6042b87 100644
--- a/drivers/serial/dz.c
+++ b/drivers/serial/dz.c
@@ -642,6 +642,26 @@
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";
@@ -738,6 +758,7 @@
.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,
@@ -861,7 +882,10 @@
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);