serial: 8250_early: Assume uart already initialized if no baud option

The <baud><parity><bit> option string is not supplied if the earlycon
is started via devicetree and OF_EARLYCON_DECLARE(). The option string
is also not required if started via kernel command line parameters of
the form:
  earlycon=uart,mmio,<addr>
  console=uart,mmio,<addr>

If earlycon_device->baud is 0, then an option string was not supplied.
In this case, assume the uart has already been initialized by the
bootloader or firmware.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 8 insertions, 2 deletions

diff --git a/drivers/tty/serial/8250/8250_early.c b/drivers/tty/serial/8250/8250_early.c
index d7b831bcf367..1701d00fd9f6 100644
--- a/drivers/tty/serial/8250/8250_early.c
+++ b/drivers/tty/serial/8250/8250_early.c
@@ -149,12 +149,18 @@ static int __init early_serial8250_setup(struct earlycon_device *device,
                 return 0;
 
         if (!device->baud) {
+                struct uart_port *port = &device->port;
+                unsigned int ier;
+
                 device->baud = probe_baud(&device->port);
                 snprintf(device->options, sizeof(device->options), "%u",
                          device->baud);
-        }
 
-        init_port(device);
+                /* assume the device was initialized, only mask interrupts */
+                ier = serial8250_early_in(port, UART_IER);
+                serial8250_early_out(port, UART_IER, ier & UART_IER_UUE);
+        } else
+                init_port(device);
 
         device->con->write = early_serial8250_write;
         return 0;