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@xxxxxxxxxxxx> for the idea of using
the scratch register canary to discover port power-down.
Cc: Doug Anderson <dianders@xxxxxxxxxxxx>
Signed-off-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
---
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
--
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