The meaning of this value is already used in several places,
but with constant values and comments to explain it separately.
It's better to have a central place to do this then use the macro
in those places for better readability.

Signed-off-by: Dingyan Li <18500469033@163.com>
---
 drivers/usb/gadget/function/f_tcm.c          | 8 ++------
 drivers/usb/gadget/function/storage_common.h | 2 +-
 drivers/usb/storage/transport.c              | 8 ++------
 include/linux/usb/storage.h                  | 8 ++++++++
 4 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/drivers/usb/gadget/function/f_tcm.c b/drivers/usb/gadget/function/f_tcm.c
index 15bb3aa12aa8..e1914b20f816 100644
--- a/drivers/usb/gadget/function/f_tcm.c
+++ b/drivers/usb/gadget/function/f_tcm.c
@@ -441,14 +441,10 @@ static int usbg_bot_setup(struct usb_function *f,
 			pr_err("No LUNs configured?\n");
 			return -EINVAL;
 		}
-		/*
-		 * If 4 LUNs are present we return 3 i.e. LUN 0..3 can be
-		 * accessed. The upper limit is 0xf
-		 */
 		luns--;
-		if (luns > 0xf) {
+		if (luns > US_BULK_MAX_LUN_LIMIT) {
 			pr_info_once("Limiting the number of luns to 16\n");
-			luns = 0xf;
+			luns = US_BULK_MAX_LUN_LIMIT;
 		}
 		ret_lun = cdev->req->buf;
 		*ret_lun = luns;
diff --git a/drivers/usb/gadget/function/storage_common.h b/drivers/usb/gadget/function/storage_common.h
index ced5d2b09234..11ac785d5eee 100644
--- a/drivers/usb/gadget/function/storage_common.h
+++ b/drivers/usb/gadget/function/storage_common.h
@@ -131,7 +131,7 @@ static inline bool fsg_lun_is_open(struct fsg_lun *curlun)
 #define FSG_BUFLEN	((u32)16384)
 
 /* Maximal number of LUNs supported in mass storage function */
-#define FSG_MAX_LUNS	16
+#define FSG_MAX_LUNS	(US_BULK_MAX_LUN_LIMIT + 1)
 
 enum fsg_buffer_state {
 	BUF_STATE_SENDING = -2,
diff --git a/drivers/usb/storage/transport.c b/drivers/usb/storage/transport.c
index 9d767f6bf722..e6bc8ecaecbb 100644
--- a/drivers/usb/storage/transport.c
+++ b/drivers/usb/storage/transport.c
@@ -1087,13 +1087,9 @@ int usb_stor_Bulk_max_lun(struct us_data *us)
 	usb_stor_dbg(us, "GetMaxLUN command result is %d, data is %d\n",
 		     result, us->iobuf[0]);
 
-	/*
-	 * If we have a successful request, return the result if valid. The
-	 * CBW LUN field is 4 bits wide, so the value reported by the device
-	 * should fit into that.
-	 */
+	/* If we have a successful request, return the result if valid. */
 	if (result > 0) {
-		if (us->iobuf[0] < 16) {
+		if (us->iobuf[0] <= US_BULK_MAX_LUN_LIMIT) {
 			return us->iobuf[0];
 		} else {
 			dev_info(&us->pusb_intf->dev,
diff --git a/include/linux/usb/storage.h b/include/linux/usb/storage.h
index 8539956bc2be..51be3bb8fccb 100644
--- a/include/linux/usb/storage.h
+++ b/include/linux/usb/storage.h
@@ -82,4 +82,12 @@ struct bulk_cs_wrap {
 #define US_BULK_RESET_REQUEST   0xff
 #define US_BULK_GET_MAX_LUN     0xfe
 
+/*
+ * If 4 LUNs are supported then the LUNs would be
+ * numbered from 0 to 3, and the return value for
+ * US_BULK_GET_MAX_LUN request would be 3. The valid
+ * LUN field is 4 bits wide, the upper limit is 0x0f.
+ */
+#define US_BULK_MAX_LUN_LIMIT   0x0f
+
 #endif
-- 
2.25.1