xhci: dbc: allow setting product string through sysfs

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>
Link: https://patch.msgid.link/20260120181148.128712-4-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/Documentation/ABI/testing/sysfs-bus-pci-drivers-xhci_hcd b/Documentation/ABI/testing/sysfs-bus-pci-drivers-xhci_hcd
index b0e8ded09c16e7da6be4cdfe37185b3ce25e64bc..d153162d60453ac997f86a5350a2e8311ba5dccf 100644 (file)
--- 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 a78d386ffdc39fe97db02ea98984d8862d8ccfef..cae98576545e18320c8137668a15f50eebe66fce 100644 (file)
--- 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