From e9a8f4d1de12633bfb71b5fee47745b32877b7b5 Mon Sep 17 00:00:00 2001 From: "Maciej W. Rozycki" Date: Wed, 23 Jul 2008 21:29:49 -0700 Subject: [PATCH] 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 Cc: Jiri Slaby Cc: Alan Cox Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- drivers/serial/dz.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/drivers/serial/dz.c b/drivers/serial/dz.c index a81d2c2ff8a2..6042b87797a1 100644 --- a/drivers/serial/dz.c +++ b/drivers/serial/dz.c @@ -642,6 +642,26 @@ static void dz_set_termios(struct uart_port *uport, struct ktermios *termios, 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 @@ 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, @@ -861,7 +882,10 @@ static int __init dz_console_setup(struct console *co, char *options) 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);