drivers: serial: ns16550: Remove hard-coded max instance count

Instead of having a hard-coded maximum instance count, introduce a
Kconfig variable for it. The inclusion of the per-instance header
files is solved by having them chain-include each other with a
pre-processor condition that checks if the current header file is the
last one or not.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>

drivers/serial/CMakeLists.txt

@@ -42,7 +42,9 @@ zephyr_library_sources_ifdef(CONFIG_USERSPACE   uart_handlers.c)
 
 if(CONFIG_UART_NS16550)
   zephyr_library_sources(uart_ns16550.c)
-  foreach(NUM RANGE 0 3)
+  math(EXPR max_index "${CONFIG_UART_NS16550_MAX_INSTANCES} - 1")
+  foreach(NUM RANGE 0 ${max_index})
+    math(EXPR NEXT_NUM "${NUM} + 1")
     configure_file(
       uart_ns16550_port_x.h
       ${PROJECT_BINARY_DIR}/include/generated/uart_ns16550_port_${NUM}.h

drivers/serial/Kconfig.ns16550

@@ -11,6 +11,13 @@ menuconfig UART_NS16550
 
 if UART_NS16550
 
+config UART_NS16550_MAX_INSTANCES
+	int "Maximum number of supported driver instances"
+	range 1 32
+	default 4
+	help
+	  The maximum number of supported driver instances in device tree.
+
 config UART_NS16550_LINE_CTRL
 	bool "Enable Serial Line Control for Apps"
 	depends on UART_LINE_CTRL

drivers/serial/uart_ns16550.c

@@ -976,7 +976,8 @@ static const struct uart_driver_api uart_ns16550_driver_api = {
 #endif
 };
 
+/* The instance-specific header files are chained together (each instance
+ * includes the next one, unless it's the last instance) so we only need to
+ * include the first instance.
+ */
 #include <uart_ns16550_port_0.h>
-#include <uart_ns16550_port_1.h>
-#include <uart_ns16550_port_2.h>
-#include <uart_ns16550_port_3.h>

drivers/serial/uart_ns16550_port_x.h

@@ -130,3 +130,8 @@ static void irq_config_func_@NUM@(const struct device *dev)
 #endif
 
 #endif
+
+/* Include subsequent instances */
+#if @NUM@ < (CONFIG_UART_NS16550_MAX_INSTANCES - 1)
+#include <uart_ns16550_port_@NEXT_NUM@.h>
+#endif