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

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

From: Łukasz Bartosik <ukaszb@chromium.org>

Add dbc_manufacturer sysfs attribute to allow changing the manufacturer
description presented by the debug device when a host requests a string
descriptor with iManufacturer 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 Foundation".
The string 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    | 13 +++++++
 drivers/usb/host/xhci-dbgcap.c                | 36 +++++++++++++++++++
 2 files changed, 49 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-bus-pci-drivers-xhci_hcd b/Documentation/ABI/testing/sysfs-bus-pci-drivers-xhci_hcd
index d153162d6045..d10e6de3adb2 100644
--- a/Documentation/ABI/testing/sysfs-bus-pci-drivers-xhci_hcd
+++ b/Documentation/ABI/testing/sysfs-bus-pci-drivers-xhci_hcd
@@ -114,3 +114,16 @@ Description:
 		connected to a USB host.
 		The default value is "Linux USB Debug Target".
 		The field length can be from 1 to 126 characters.
+
+What:		/sys/bus/pci/drivers/xhci_hcd/.../dbc_manufacturer
+Date:		January 2026
+Contact:	Łukasz Bartosik <ukaszb@chromium.org>
+Description:
+		The dbc_manufacturer attribute allows to change the manufacturer
+		string descriptor presented by the debug device when a host
+		requests a string descriptor with iManufacturer 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 Foundation".
+		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 cae98576545e..9fd497e0dc7f 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_manufacturer_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.manufacturer);
+}
+
+static ssize_t dbc_manufacturer_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.manufacturer, buf, len);
+	dbc->str.manufacturer[len] = '\0';
+
+	return size;
+}
+
 static ssize_t dbc_product_show(struct device *dev,
 				 struct device_attribute *attr,
 				 char *buf)
@@ -1367,6 +1401,7 @@ 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_manufacturer);
 static DEVICE_ATTR_RW(dbc_bInterfaceProtocol);
 static DEVICE_ATTR_RW(dbc_poll_interval_ms);
 
@@ -1377,6 +1412,7 @@ static struct attribute *dbc_dev_attrs[] = {
 	&dev_attr_dbc_bcdDevice.attr,
 	&dev_attr_dbc_serial.attr,
 	&dev_attr_dbc_product.attr,
+	&dev_attr_dbc_manufacturer.attr,
 	&dev_attr_dbc_bInterfaceProtocol.attr,
 	&dev_attr_dbc_poll_interval_ms.attr,
 	NULL
-- 
2.43.0