When using no_console_suspend, the serial console may be powered off anyway during system sleep. Upon resume, the port may be in its default power-on state, but is expected to continue console i/o before the device has received its pm callback. The resultant garbage i/o can cause all kinds of havoc on the remote end.
Use the scratch register as a canary to discover if the console has been powered-off. Write a non-zero value to the scratch register at port suspend and reprogram the port before any console i/o if the scratch register != canary before port resume. This workaround is disabled for omap_8250 (which uses different divisor programming). Credit to Doug Anderson <[email protected]> for the idea of using the scratch register canary to discover port power-down. Cc: Doug Anderson <[email protected]> Signed-off-by: Peter Hurley <[email protected]> --- drivers/tty/serial/8250/8250_core.c | 35 ++++++++++++++++++++++++++++++++++- include/linux/serial_8250.h | 3 +++ 2 files changed, 37 insertions(+), 1 deletion(-) diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c index 5240c1a..8fd4b57 100644 --- a/drivers/tty/serial/8250/8250_core.c +++ b/drivers/tty/serial/8250/8250_core.c @@ -3244,6 +3244,27 @@ serial8250_console_write(struct console *co, const char *s, unsigned int count) else serial_port_out(port, UART_IER, 0); + /* check scratch reg to see if port powered off during system sleep */ + if (up->canary && (up->canary != serial_port_in(port, UART_SCR))) { + struct ktermios termios; + unsigned int baud, quot, frac = 0; + + termios.c_cflag = port->cons->cflag; + if (port->state->port.tty && termios.c_cflag == 0) + termios.c_cflag = port->state->port.tty->termios.c_cflag; + + baud = uart_get_baud_rate(port, &termios, NULL, + port->uartclk / 16 / 0xffff, + port->uartclk / 16); + quot = serial8250_get_divisor(up, baud, &frac); + + serial8250_set_divisor(port, baud, quot, frac); + serial_port_out(port, UART_LCR, up->lcr); + serial_port_out(port, UART_MCR, UART_MCR_DTR | UART_MCR_RTS); + + up->canary = 0; + } + uart_console_write(port, s, count, serial8250_console_putchar); /* @@ -3394,7 +3415,17 @@ int __init early_serial_setup(struct uart_port *port) */ void serial8250_suspend_port(int line) { - uart_suspend_port(&serial8250_reg, &serial8250_ports[line].port); + struct uart_8250_port *up = &serial8250_ports[line]; + struct uart_port *port = &up->port; + + if (!console_suspend_enabled && uart_console(port) && + port->type != PORT_8250) { + unsigned char canary = 0xa5; + serial_out(up, UART_SCR, canary); + up->canary = canary; + } + + uart_suspend_port(&serial8250_reg, port); } /** @@ -3408,6 +3439,8 @@ void serial8250_resume_port(int line) struct uart_8250_port *up = &serial8250_ports[line]; struct uart_port *port = &up->port; + up->canary = 0; + if (up->capabilities & UART_NATSEMI) { /* Ensure it's still in high speed mode */ serial_port_out(port, UART_LCR, 0xE0); diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h index 245b959..a8efa23 100644 --- a/include/linux/serial_8250.h +++ b/include/linux/serial_8250.h @@ -85,6 +85,9 @@ struct uart_8250_port { unsigned char mcr_force; /* mask of forced bits */ unsigned char cur_iotype; /* Running I/O type */ unsigned int rpm_tx_active; + unsigned char canary; /* non-zero during system sleep + * if no_console_suspend + */ /* * Some bits in registers are cleared on a read, so they must -- 2.2.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
