[PATCH 4.0 172/220] serial: 8250: Check UART_SCR is writable

[Greg Kroah-Hartman]

4.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>

commit f01a0bd8921b9d6668d41fae3198970e6318f532 upstream.

Au1x00/RT2800+ doesn't implement the 8250 scratch register (and
this may be true of other h/w currently supported by the 8250 driver);
read back the canary value written to the scratch register to enable
the console h/w restart after resume from system suspend.

Fixes: 4516d50aabedb ("serial: 8250: Use canary to restart console ...")
Reported-by: Mason <slash.tmp@xxxxxxx>
Signed-off-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/tty/serial/8250/8250_core.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -3444,7 +3444,8 @@ void serial8250_suspend_port(int line)
 	    port->type != PORT_8250) {
 		unsigned char canary = 0xa5;
 		serial_out(up, UART_SCR, canary);
-		up->canary = canary;
+		if (serial_in(up, UART_SCR) == canary)
+			up->canary = canary;
 	}
 
 	uart_suspend_port(&serial8250_reg, port);


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