8250: Make SERIAL_8250_RUNTIME_UARTS work correctly

Consider a situation where I have an ARM based system (such as the
Zynq) and therefore no legacy ports. I have three memory-mapped ports
(such as cRIO-9068). I use device tree to describe the ports. What
would be the config options I set so that I get only the three ports in
my system? I do not want legacy ports being created automatically and I
want it to be flexible enough that it creates the devices based only on
the device tree. I expected setting SERIAL_8250_RUNTIME_UARTS = 0 to
work because the description said, "Set this to the maximum number of
serial ports you want the kernel to register at boot time."
Unfortunately, even though SERIAL_8250_NR_UARTS was set to the default
value of 4, I did not get any device nodes (because
SERIAL_8250_RUNTIME_UARTS was 0). This is what this change is
addressing.

SERIAL_8250_NR_UARTS controls the maximum number of ports you can
support. SERIAL_8250_RUNTIME_UARTS specifies the number of ports you
want to create automatically for legacy ports at boot time. All other
ports will be created when serial8250_register_port is called (and if
it does not exceed the total number of supported ports as specified by
SERIAL_8250_NR_UARTS).

Signed-off-by: Karthik Manamcheri <karthik.manamcheri@ni.com>
Acked-by: Jaeden Amero <jaeden.amero@ni.com>

Author: Karthik Manamcheri

drivers/tty/serial/8250/8250_core.c

@@ -505,7 +505,7 @@ static void __init serial8250_isa_init_ports(void)
 	if (nr_uarts > UART_NR)
 		nr_uarts = UART_NR;
 
-	for (i = 0; i < nr_uarts; i++) {
+	for (i = 0; i < UART_NR; i++) {
 		struct uart_8250_port *up = &serial8250_ports[i];
 		struct uart_port *port = &up->port;
 
@@ -606,7 +606,7 @@ static int univ8250_console_setup(struct console *co, char *options)
 	 * if so, search for the first available port that does have
 	 * console support.
 	 */
-	if (co->index >= nr_uarts)
+	if (co->index >= UART_NR)
 		co->index = 0;
 	port = &serial8250_ports[co->index].port;
 	/* link port to console */
@@ -659,7 +659,7 @@ static int univ8250_console_match(struct console *co, char *name, int idx,
 		return -ENODEV;
 
 	/* try to match the port specified on the command line */
-	for (i = 0; i < nr_uarts; i++) {
+	for (i = 0; i < UART_NR; i++) {
 		struct uart_port *port = &serial8250_ports[i].port;
 
 		if (port->iotype != iotype)
@@ -867,7 +867,7 @@ static int serial8250_remove(struct platform_device *dev)
 {
 	int i;
 
-	for (i = 0; i < nr_uarts; i++) {
+	for (i = 0; i < UART_NR; i++) {
 		struct uart_8250_port *up = &serial8250_ports[i];
 
 		if (up->port.dev == &dev->dev)
@@ -934,7 +934,7 @@ static struct uart_8250_port *serial8250_find_match_or_unused(const struct uart_
 	/*
 	 * First, find a port entry which matches.
 	 */
-	for (i = 0; i < nr_uarts; i++)
+	for (i = 0; i < UART_NR; i++)
 		if (uart_match_port(&serial8250_ports[i].port, port))
 			return &serial8250_ports[i];
 
@@ -948,7 +948,7 @@ static struct uart_8250_port *serial8250_find_match_or_unused(const struct uart_
 	 * free entry.  We look for one which hasn't been previously
 	 * used (indicated by zero iobase).
 	 */
-	for (i = 0; i < nr_uarts; i++)
+	for (i = 0; i < UART_NR; i++)
 		if (serial8250_ports[i].port.type == PORT_UNKNOWN &&
 		    serial8250_ports[i].port.iobase == 0)
 			return &serial8250_ports[i];
@@ -957,7 +957,7 @@ static struct uart_8250_port *serial8250_find_match_or_unused(const struct uart_
 	 * That also failed.  Last resort is to find any entry which
 	 * doesn't have a real port associated with it.
 	 */
-	for (i = 0; i < nr_uarts; i++)
+	for (i = 0; i < UART_NR; i++)
 		if (serial8250_ports[i].port.type == PORT_UNKNOWN)
 			return &serial8250_ports[i];