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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>
This commit is contained in:
Maciej W. Rozycki 2008-07-23 21:29:49 -07:00 committed by Linus Torvalds
parent 3771359128
commit e9a8f4d1de
1 changed files with 24 additions and 0 deletions
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24
drivers/serial/dz.c
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@ -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);