[PATCH 3/4] xhci: dbc: allow setting product string through sysfs

[Mathias Nyman <mathias.nyman@linux.intel.com>]

From: Łukasz Bartosik <ukaszb@chromium.org>

Add dbc_product sysfs attribute to allow changing the product description
presented by the debug device when a host requests a string descriptor
with iProduct index.

Value can only be changed while debug capability (DbC) is in disabled
state to prevent USB device descriptor change while connected to a USB
host.

The default value is "Linux USB Debug Target".
The field length can be from 1 to 126 characters.
String is terminated at null or newline, driver does not support empty
string.

[ mn: Improve commit message and sysfs entry documentation ]
Signed-off-by: Łukasz Bartosik <ukaszb@chromium.org>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
---
 .../testing/sysfs-bus-pci-drivers-xhci_hcd    | 14 ++++++++
 drivers/usb/host/xhci-dbgcap.c                | 36 +++++++++++++++++++
 2 files changed, 50 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-bus-pci-drivers-xhci_hcd b/Documentation/ABI/testing/sysfs-bus-pci-drivers-xhci_hcd
index b0e8ded09c16..d153162d6045 100644
--- a/Documentation/ABI/testing/sysfs-bus-pci-drivers-xhci_hcd
+++ b/Documentation/ABI/testing/sysfs-bus-pci-drivers-xhci_hcd
@@ -100,3 +100,17 @@ Description:
 		connected to a USB host.
 		The default value is "0001".
 		The field length can be from 1 to 126 characters.
+
+What:		/sys/bus/pci/drivers/xhci_hcd/.../dbc_product
+Date:		January 2026
+Contact:	Łukasz Bartosik <ukaszb@chromium.org>
+Description:
+		The dbc_product attribute allows to change the product string
+		descriptor presented by the debug device when a host requests
+		a string descriptor with iProduct index.
+		Index is found in the iProduct field in the device descriptor.
+		Value can only be changed while debug capability (DbC) is in
+		disabled state to prevent USB device descriptor change while
+		connected to a USB host.
+		The default value is "Linux USB Debug Target".
+		The field length can be from 1 to 126 characters.
diff --git a/drivers/usb/host/xhci-dbgcap.c b/drivers/usb/host/xhci-dbgcap.c
index a78d386ffdc3..cae98576545e 100644
--- a/drivers/usb/host/xhci-dbgcap.c
+++ b/drivers/usb/host/xhci-dbgcap.c
@@ -1210,6 +1210,40 @@ static ssize_t dbc_bcdDevice_store(struct device *dev,
 	return size;
 }
 
+static ssize_t dbc_product_show(struct device *dev,
+				 struct device_attribute *attr,
+				 char *buf)
+{
+	struct xhci_hcd	*xhci = hcd_to_xhci(dev_get_drvdata(dev));
+	struct xhci_dbc	*dbc = xhci->dbc;
+
+	return sysfs_emit(buf, "%s\n", dbc->str.product);
+}
+
+static ssize_t dbc_product_store(struct device *dev,
+				  struct device_attribute *attr,
+				  const char *buf, size_t size)
+{
+	struct xhci_hcd	*xhci = hcd_to_xhci(dev_get_drvdata(dev));
+	struct xhci_dbc	*dbc = xhci->dbc;
+	size_t len;
+
+	if (dbc->state != DS_DISABLED)
+		return -EBUSY;
+
+	len = strcspn(buf, "\n");
+	if (!len)
+		return -EINVAL;
+
+	if (len > USB_MAX_STRING_LEN)
+		return -E2BIG;
+
+	memcpy(dbc->str.product, buf, len);
+	dbc->str.product[len] = '\0';
+
+	return size;
+}
+
 static ssize_t dbc_serial_show(struct device *dev,
 			    struct device_attribute *attr,
 			    char *buf)
@@ -1332,6 +1366,7 @@ static DEVICE_ATTR_RW(dbc_idVendor);
 static DEVICE_ATTR_RW(dbc_idProduct);
 static DEVICE_ATTR_RW(dbc_bcdDevice);
 static DEVICE_ATTR_RW(dbc_serial);
+static DEVICE_ATTR_RW(dbc_product);
 static DEVICE_ATTR_RW(dbc_bInterfaceProtocol);
 static DEVICE_ATTR_RW(dbc_poll_interval_ms);
 
@@ -1341,6 +1376,7 @@ static struct attribute *dbc_dev_attrs[] = {
 	&dev_attr_dbc_idProduct.attr,
 	&dev_attr_dbc_bcdDevice.attr,
 	&dev_attr_dbc_serial.attr,
+	&dev_attr_dbc_product.attr,
 	&dev_attr_dbc_bInterfaceProtocol.attr,
 	&dev_attr_dbc_poll_interval_ms.attr,
 	NULL
-- 
2.43.0