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-rw-r--r--include/linux/serial_core.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index f9d7f0a625fd..3b64c9a26945 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -470,6 +470,7 @@ struct uart_port {
unsigned char iotype; /* io access style */
+#define UPIO_UNKNOWN ((unsigned char)~0U) /* UCHAR_MAX */
#define UPIO_PORT (SERIAL_IO_PORT) /* 8b I/O port access */
#define UPIO_HUB6 (SERIAL_IO_HUB6) /* Hub6 ISA card */
#define UPIO_MEM (SERIAL_IO_MEM) /* driver-specific */