linux-kernel - [PATCH] usb: gadget: configfs: Correctly set use_os

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Message-Id: <1755833769-25434-1-git-send-email-william.wu@rock-chips.com>
Date: Fri, 22 Aug 2025 11:36:09 +0800
From: William Wu <william.wu@...k-chips.com>
To: gregkh@...uxfoundation.org
Cc: linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	william.wu@...k-chips.com,
	frank.wang@...k-chips.com,
	jianwei.zheng@...k-chips.com,
	yue.long@...k-chips.com
Subject: [PATCH] usb: gadget: configfs: Correctly set use_os_string at bind

Once the use_os_string flag is set to true for some functions
(e.g. adb/mtp) which need to response the OS string, and then
if we re-bind the ConfigFS gadget to use the other functions
(e.g. hid) which should not to response the OS string, however,
because the use_os_string flag is still true, so the usb gadget
response the OS string descriptor incorrectly, this can cause
the USB device to be unrecognizable on the Windows system.

An example of this as follows:

echo 1 > os_desc/use
ln -s functions/ffs.adb configs/b.1/function0
start adbd
echo "<udc device>" > UDC   #succeed

stop adbd
rm configs/b.1/function0
echo 0 > os_desc/use
ln -s functions/hid.gs0 configs/b.1/function0
echo "<udc device>" > UDC  #fail to connect on Windows

This patch sets the use_os_string flag to false at bind if
the functions not support OS Descriptors.

Signed-off-by: William Wu <william.wu@...k-chips.com>
---
 drivers/usb/gadget/configfs.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/usb/gadget/configfs.c b/drivers/usb/gadget/configfs.c
index f94ea19..6bcac85 100644
--- a/drivers/usb/gadget/configfs.c
+++ b/drivers/usb/gadget/configfs.c
@@ -1750,6 +1750,8 @@ static int configfs_composite_bind(struct usb_gadget *gadget,
 		cdev->use_os_string = true;
 		cdev->b_vendor_code = gi->b_vendor_code;
 		memcpy(cdev->qw_sign, gi->qw_sign, OS_STRING_QW_SIGN_LEN);
+	} else {
+		cdev->use_os_string = false;
 	}
 
 	if (gadget_is_otg(gadget) && !otg_desc[0]) {
-- 
2.0.0