serial: core: Add UPIO_UNKNOWN constant for unknown port type

In some APIs we would like to assign the special value to iotype
and compare against it in another places. Introduce UPIO_UNKNOWN
for this purpose.

Note, we can't use 0, because it's a valid value for IO port access.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20240304123035.758700-3-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index f9d7f0a625fdd5f4022e366005c97b5ae6f1a0f1..3b64c9a2694580d8ecd163cc0e4953b62977960d 100644 (file)
--- 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 */