serial: 8250: Use canary to restart console after suspend
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>
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 @@
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