1 files changed, 6 insertions, 2 deletions

diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c
index 5261f0af8b10..2964ca9df5a0 100644
--- a/drivers/serial/8250.c
+++ b/drivers/serial/8250.c
@@ -920,12 +920,16 @@ static void autoconfig(struct uart_8250_port *up, unsigned int probeflags)
 #ifdef __i386__
                 outb(0xff, 0x080);
 #endif
-                scratch2 = serial_inp(up, UART_IER);
+                /*
+                 * 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_inp(up, UART_IER) & 0x0f;
                 serial_outp(up, UART_IER, 0x0F);
 #ifdef __i386__
                 outb(0, 0x080);
 #endif
-                scratch3 = serial_inp(up, UART_IER);
+                scratch3 = serial_inp(up, UART_IER) & 0x0f;
                 serial_outp(up, UART_IER, scratch);
                 if (scratch2 != 0 || scratch3 != 0x0F) {
                         /*