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serial: 8250: Check UART_SCR is writable

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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: 4516d50aab ("serial: 8250: Use canary to restart console ...")
Reported-by: Mason <slash.tmp@free.fr>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Hurley 2015-03-09 14:05:01 -04:00 committed by Greg Kroah-Hartman
parent 509cb7dc07
commit f01a0bd892
1 changed files with 2 additions and 1 deletions
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3
drivers/tty/serial/8250/8250_core.c
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@ -3585,7 +3585,8 @@ 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);