linux-kernel - [PATCH v1] usb: storage: add a macro for the upper limit of max LUN

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Message-Id: <20241030083858.46907-1-18500469033@163.com>
Date: Wed, 30 Oct 2024 16:38:58 +0800
From: Dingyan Li <18500469033@....com>
To: gregkh@...uxfoundation.org,
	stern@...land.harvard.edu
Cc: linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	usb-storage@...ts.one-eyed-alien.net
Subject: [PATCH v1] usb: storage: add a macro for the upper limit of max LUN

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@....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