From 412de639b55fcf1ab5ad50a6be84f5164104abe3 Mon Sep 17 00:00:00 2001 From: =?utf8?q?=C5=81ukasz=20Bartosik?= Date: Tue, 20 Jan 2026 20:11:46 +0200 Subject: [PATCH] xhci: dbc: allow setting device serial number through sysfs MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Add dbc_serial sysfs attribute to allow changing the serial number string descriptor presented by the debug device when a host requests a string descriptor with iSerialNumber 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 "0001". 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 Signed-off-by: Mathias Nyman Link: https://patch.msgid.link/20260120181148.128712-3-mathias.nyman@linux.intel.com Signed-off-by: Greg Kroah-Hartman --- .../testing/sysfs-bus-pci-drivers-xhci_hcd | 15 ++++++++ drivers/usb/host/xhci-dbgcap.c | 36 +++++++++++++++++++ 2 files changed, 51 insertions(+) diff --git a/Documentation/ABI/testing/sysfs-bus-pci-drivers-xhci_hcd b/Documentation/ABI/testing/sysfs-bus-pci-drivers-xhci_hcd index fc82aa4e54b0..b0e8ded09c16 100644 --- a/Documentation/ABI/testing/sysfs-bus-pci-drivers-xhci_hcd +++ b/Documentation/ABI/testing/sysfs-bus-pci-drivers-xhci_hcd @@ -85,3 +85,18 @@ Description: up to 5000. The default value is 64 ms. This polling interval is used while DbC is enabled but has no active data transfers. + +What: /sys/bus/pci/drivers/xhci_hcd/.../dbc_serial +Date: January 2026 +Contact: Łukasz Bartosik +Description: + The dbc_serial attribute allows to change the serial number + string descriptor presented by the debug device when a host + requests a string descriptor with iSerialNumber index. + Index is found in the iSerialNumber 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 "0001". + 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 4ba8edb37e51..a78d386ffdc3 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_serial_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.serial); +} + +static ssize_t dbc_serial_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.serial, buf, len); + dbc->str.serial[len] = '\0'; + + return size; +} + static ssize_t dbc_bInterfaceProtocol_show(struct device *dev, struct device_attribute *attr, char *buf) @@ -1297,6 +1331,7 @@ static DEVICE_ATTR_RW(dbc); 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_bInterfaceProtocol); static DEVICE_ATTR_RW(dbc_poll_interval_ms); @@ -1305,6 +1340,7 @@ static struct attribute *dbc_dev_attrs[] = { &dev_attr_dbc_idVendor.attr, &dev_attr_dbc_idProduct.attr, &dev_attr_dbc_bcdDevice.attr, + &dev_attr_dbc_serial.attr, &dev_attr_dbc_bInterfaceProtocol.attr, &dev_attr_dbc_poll_interval_ms.attr, NULL -- 2.47.3