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serial: 8250: Use canary to restart console after suspend

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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 <dianders@chromium.org> for the idea of using
the scratch register canary to discover port power-down.

Cc: Doug Anderson <dianders@chromium.org>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Hurley 2015-01-22 12:24:30 -05:00 committed by Greg Kroah-Hartman
parent 06a4c71067
commit 4516d50aab
2 changed files with 37 additions and 1 deletions
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35
drivers/tty/serial/8250/8250_core.c
View File

@ -3267,6 +3267,27 @@ 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);
/*
@ -3417,7 +3438,17 @@ 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);
}
/**
@ -3431,6 +3462,8 @@ 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);

3
include/linux/serial_8250.h
View File

@ -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