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| author | Maciej W. Rozycki <macro@linux-mips.org> | 2008-07-23 21:29:49 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2008-07-24 10:47:29 -0700 |
| commit | e9a8f4d1de12633bfb71b5fee47745b32877b7b5 (patch) | |
| tree | 3bf0f747b32314491b9b6cf4f44a2c6d3288390e /drivers/serial | |
| parent | 377135912806ddc87d56d64fafa685f4063c45f1 (diff) | |
| download | linux-stable-e9a8f4d1de12633bfb71b5fee47745b32877b7b5.tar.gz linux-stable-e9a8f4d1de12633bfb71b5fee47745b32877b7b5.tar.bz2 linux-stable-e9a8f4d1de12633bfb71b5fee47745b32877b7b5.zip | |
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>
Diffstat (limited to 'drivers/serial')
| -rw-r--r-- | drivers/serial/dz.c | 24 |
1 files changed, 24 insertions, 0 deletions
diff --git a/drivers/serial/dz.c b/drivers/serial/dz.c index a81d2c2ff8a2..6042b87797a1 100644 --- a/drivers/serial/dz.c +++ b/drivers/serial/dz.c @@ -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); |