diff options
| author | Maciej W. Rozycki <macro@linux-mips.org> | 2008-07-23 21:29:48 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2008-07-24 10:47:29 -0700 |
| commit | 377135912806ddc87d56d64fafa685f4063c45f1 (patch) | |
| tree | 77165d6a19281278d54c0b054ffacf7472bd093e /drivers/serial/zs.c | |
| parent | b76c5a0717094f0a900d9afd8e36f7ad8dbba587 (diff) | |
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: 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>
Diffstat (limited to 'drivers/serial/zs.c')
| -rw-r--r-- | drivers/serial/zs.c | 21 |
1 files changed, 19 insertions, 2 deletions
diff --git a/drivers/serial/zs.c b/drivers/serial/zs.c index bd45b6230fd..9e6a873f820 100644 --- a/drivers/serial/zs.c +++ b/drivers/serial/zs.c @@ -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); |