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Commit 37713591 authored by Maciej W. Rozycki's avatar Maciej W. Rozycki Committed by Linus Torvalds
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serial: Z85C30: 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 Zilog
Z85C30 SCC 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 not a bug in the
firmware, as some registers it would have to examine are write-only.

This is a workaround for the Z85C30 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 b76c5a07

drivers/serial/zs.c

+19 −2
Original line number Diff line number Diff line
@@ -787,7 +787,6 @@ static int zs_startup(struct uart_port *uport) 
	zport->regs[1] &= ~RxINT_MASK;

	zport->regs[1] |= RxINT_ALL | TxINT_ENAB | EXT_INT_ENAB;

	zport->regs[3] |= RxENABLE;

	zport->regs[5] |= TxENAB;

	zport->regs[15] |= BRKIE;

	write_zsreg(zport, R1, zport->regs[1]);

	write_zsreg(zport, R3, zport->regs[3]);
@@ -814,7 +813,6 @@ static void zs_shutdown(struct uart_port *uport) 


	spin_lock_irqsave(&scc->zlock, flags);



	zport->regs[5] &= ~TxENAB;

	zport->regs[3] &= ~RxENABLE;

	write_zsreg(zport, R5, zport->regs[5]);

	write_zsreg(zport, R3, zport->regs[3]);
@@ -959,6 +957,23 @@ static void zs_set_termios(struct uart_port *uport, struct ktermios *termios, 
	spin_unlock_irqrestore(&scc->zlock, flags);

}



/*

 * Hack alert!

 * Required solely so that the initial PROM-based console

 * works undisturbed in parallel with this one.

 */

static void zs_pm(struct uart_port *uport, unsigned int state,

		  unsigned int oldstate)

{

	struct zs_port *zport = to_zport(uport);



	if (state < 3)

		zport->regs[5] |= TxENAB;

	else

		zport->regs[5] &= ~TxENAB;

	write_zsreg(zport, R5, zport->regs[5]);

}





static const char *zs_type(struct uart_port *uport)

{
@@ -1041,6 +1056,7 @@ static struct uart_ops zs_ops = { 
	.startup	= zs_startup,

	.shutdown	= zs_shutdown,

	.set_termios	= zs_set_termios,

	.pm		= zs_pm,

	.type		= zs_type,

	.release_port	= zs_release_port,

	.request_port	= zs_request_port,
@@ -1190,6 +1206,7 @@ static int __init zs_console_setup(struct console *co, char *options) 
		return ret;



	zs_reset(zport);

	zs_pm(uport, 0, -1);



	if (options)

		uart_parse_options(options, &baud, &parity, &bits, &flow);