serial: 8250: Use defined IER bits

Instead of literal 0x0f, add a define for enabling all IER bits the
8250 driver is interested in.

Don't make the define for combined flags part of UAPI.
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20221125130509.8482-2-ilpo.jarvinen@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_port.c

@@ -1236,14 +1236,14 @@ static void autoconfig(struct uart_8250_port *up)
 		 * Mask out IER[7:4] bits for test as some UARTs (e.g. TL
 		 * 16C754B) allow only to modify them if an EFR bit is set.
 		 */
-		scratch2 = serial_in(up, UART_IER) & 0x0f;
-		serial_out(up, UART_IER, 0x0F);
+		scratch2 = serial_in(up, UART_IER) & UART_IER_ALL_INTR;
+		serial_out(up, UART_IER, UART_IER_ALL_INTR);
 #ifdef __i386__
 		outb(0, 0x080);
 #endif
-		scratch3 = serial_in(up, UART_IER) & 0x0f;
+		scratch3 = serial_in(up, UART_IER) & UART_IER_ALL_INTR;
 		serial_out(up, UART_IER, scratch);
-		if (scratch2 != 0 || scratch3 != 0x0F) {
+		if (scratch2 != 0 || scratch3 != UART_IER_ALL_INTR) {
 			/*
 			 * We failed; there's nothing here
 			 */
@@ -1394,7 +1394,7 @@ static void autoconfig_irq(struct uart_8250_port *up)
 		serial8250_out_MCR(up,
 			UART_MCR_DTR | UART_MCR_RTS | UART_MCR_OUT2);
 	}
-	serial_out(up, UART_IER, 0x0f);	/* enable all intrs */
+	serial_out(up, UART_IER, UART_IER_ALL_INTR);
 	serial_in(up, UART_LSR);
 	serial_in(up, UART_RX);
 	serial_in(up, UART_IIR);

include/linux/serial.h

@@ -12,6 +12,11 @@
 #include <uapi/linux/serial.h>
 #include <uapi/linux/serial_reg.h>
 
+#define UART_IER_ALL_INTR	(UART_IER_MSI | \
+				 UART_IER_RLSI | \
+				 UART_IER_THRI | \
+				 UART_IER_RDI)
+
 /* Helper for dealing with UART_LCR_WLEN* defines */
 #define UART_LCR_WLEN(x)	((x) - 5)