serial: Z85C30: avoid a hang at console switch-over (37713591) · Commits · 戴 / test

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:

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>

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);

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