GPIB secondary addresses can be between 0 and 31 inclusive
unlike primary addresses where address 31 is not a valid device
address.  When 31 is used as a primary talk address it
forms the UNT (Untalk) command and when used as a listener address it
forms the UNL (Unlisten) commmand.
The library was incorrectly not allowing a secondary address
with a value of 31 to be used.

Fixes: 9dde4559e939 ("staging: gpib: Add GPIB common core driver")
Signed-off-by: Dave Penkler <dpenkler@gmail.com>
---
 drivers/staging/gpib/common/gpib_os.c | 4 +---
 drivers/staging/gpib/common/iblib.c   | 6 +++---
 drivers/staging/gpib/common/ibsys.h   | 3 +++
 3 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/staging/gpib/common/gpib_os.c b/drivers/staging/gpib/common/gpib_os.c
index e84097ac8f69..0285180ae1f0 100644
--- a/drivers/staging/gpib/common/gpib_os.c
+++ b/drivers/staging/gpib/common/gpib_os.c
@@ -525,8 +525,6 @@ int serial_poll_all(gpib_board_t *board, unsigned int usec_timeout)
  * SPD and UNT are sent at the completion of the poll.
  */
 
-static const int gpib_addr_max = 30;	/* max address for primary/secondary gpib addresses */
-
 int dvrsp(gpib_board_t *board, unsigned int pad, int sad,
 	  unsigned int usec_timeout, uint8_t *result)
 {
@@ -538,7 +536,7 @@ int dvrsp(gpib_board_t *board, unsigned int pad, int sad,
 		return -1;
 	}
 
-	if (pad > gpib_addr_max || sad > gpib_addr_max) {
+	if (pad > MAX_GPIB_PRIMARY_ADDRESS || sad > MAX_GPIB_SECONDARY_ADDRESS) {
 		pr_err("gpib: bad address for serial poll");
 		return -1;
 	}
diff --git a/drivers/staging/gpib/common/iblib.c b/drivers/staging/gpib/common/iblib.c
index fc57e760c144..db1911cc1b26 100644
--- a/drivers/staging/gpib/common/iblib.c
+++ b/drivers/staging/gpib/common/iblib.c
@@ -479,7 +479,7 @@ int ibsre(gpib_board_t *board, int enable)
  */
 int ibpad(gpib_board_t *board, unsigned int addr)
 {
-	if (addr > 30) {
+	if (addr > MAX_GPIB_PRIMARY_ADDRESS) {
 		pr_err("gpib: invalid primary address %u\n", addr);
 		return -1;
 	}
@@ -498,8 +498,8 @@ int ibpad(gpib_board_t *board, unsigned int addr)
  */
 int ibsad(gpib_board_t *board, int addr)
 {
-	if (addr > 30) {
-		pr_err("gpib: invalid secondary address %i, must be 0-30\n", addr);
+	if (addr > MAX_GPIB_SECONDARY_ADDRESS) {
+		pr_err("gpib: invalid secondary address %i\n", addr);
 		return -1;
 	}
 	board->sad = addr;
diff --git a/drivers/staging/gpib/common/ibsys.h b/drivers/staging/gpib/common/ibsys.h
index b78ca5ea4da1..da20971e9c7e 100644
--- a/drivers/staging/gpib/common/ibsys.h
+++ b/drivers/staging/gpib/common/ibsys.h
@@ -16,6 +16,9 @@
 #include <asm/irq.h>
 #include <asm/dma.h>
 
+#define MAX_GPIB_PRIMARY_ADDRESS 30
+#define MAX_GPIB_SECONDARY_ADDRESS 31
+
 int gpib_allocate_board(gpib_board_t *board);
 void gpib_deallocate_board(gpib_board_t *board);
 
-- 
2.46.2