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Commit e9a8f4d1 authored by Maciej W. Rozycki's avatar Maciej W. Rozycki Committed by Linus Torvalds
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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: default avatarMaciej W. Rozycki <macro@linux-mips.org>
Cc: Jiri Slaby <jirislaby@gmail.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 37713591

drivers/serial/dz.c

+24 −0
Original line number Diff line number Diff line
@@ -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);