platform/x86: thinkpad_acpi: Add USB-C Security (USCS) support

Newer ThinkPad systems expose a USB-C Security (Restricted Mode) feature.
When active, USB-C data connections are disabled while power delivery is
preserved. This is useful for kiosk and physically-secured deployments.

Hardware interface:

The HKEY device exposes a read-only ACPI method USCS():

  Return value bit layout:
    Bit 16 : Capability flag (1 = feature present on this SKU)
    Bit  0 : Current state  (0 = security OFF, 1 = security ON)

The sysfs attribute is read-only.

The Fn+U followed by Fn+S hotkey chord is the only way to toggle the
hardware state.

Hotkey:

Fn+U followed by Fn+S generates HKEY event 0x131e.

sysfs interface:

  /sys/devices/platform/thinkpad_acpi/usb_c_security  (read-only)
  "enabled\n"  -- data connections are currently blocked
  "disabled\n" -- data connections are currently allowed

  The attribute is hidden on SKUs where the USCS capability bit (bit 16)
  is not set, so there is no ABI impact on unsupported hardware.

Suggested-by: Mark Pearson <mpearson-lenovo@squebb.ca>
Signed-off-by: Vishnu Sankar <vishnuocv@gmail.com>
Link: https://patch.msgid.link/20260709021504.465792-1-vishnuocv@gmail.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

1 files changed, 117 insertions, 0 deletions

diff --git a/drivers/platform/x86/lenovo/thinkpad_acpi.c b/drivers/platform/x86/lenovo/thinkpad_acpi.c
index f614b2701d48..6dd7c28fc0db 100644
--- a/drivers/platform/x86/lenovo/thinkpad_acpi.c
+++ b/drivers/platform/x86/lenovo/thinkpad_acpi.c
@@ -38,6 +38,7 @@
 #include <linux/backlight.h>
 #include <linux/bitfield.h>
 #include <linux/bitops.h>
+#include <linux/cleanup.h>
 #include <linux/debugfs.h>
 #include <linux/delay.h>
 #include <linux/dmi.h>
@@ -67,6 +68,7 @@
 #include <linux/seq_file.h>
 #include <linux/slab.h>
 #include <linux/string.h>
+#include <linux/string_choices.h>
 #include <linux/string_helpers.h>
 #include <linux/sysfs.h>
 #include <linux/types.h>
@@ -186,6 +188,7 @@ enum tpacpi_hkey_event_t {
 	TP_HKEY_EV_AMT_TOGGLE		= 0x131a, /* Toggle AMT on/off */
 	TP_HKEY_EV_CAMERASHUTTER_TOGGLE = 0x131b, /* Toggle Camera Shutter */
 	TP_HKEY_EV_DOUBLETAP_TOGGLE	= 0x131c, /* Toggle trackpoint doubletap on/off */
+	TP_HKEY_EV_USB_C_SECURITY	= 0x131e, /* USB C Security (Fn+U, Fn+S) */
 	TP_HKEY_EV_PROFILE_TOGGLE	= 0x131f, /* Toggle platform profile in 2024 systems */
 	TP_HKEY_EV_PROFILE_TOGGLE2	= 0x1401, /* Toggle platform profile in 2025 + systems */
 
@@ -375,6 +378,8 @@ static struct {
 	u32 has_adaptive_kbd:1;
 	u32 kbd_lang:1;
 	u32 trackpoint_doubletap_enable:1;
+	u32 usbc_security_supported:1;
+	bool usbc_security_enabled;
 	struct quirk_entry *quirks;
 } tp_features;
 
@@ -11285,6 +11290,111 @@ static struct ibm_struct hwdd_driver_data = {
 	.name = "hwdd",
 };
 
+/*************************************************************************
+ * USB-C Security subdriver
+ *
+ * HKEY.USCS(0) is a read-only ACPI method; its argument is ignored.
+ * It always returns:
+ *   bit 16 - USB-C security capability present on this SKU or not
+ *   bit  0 - USB-C Security state (enable or disable)
+ *
+ * Hotkey
+ * ------
+ * 0x131e (Fn+U, Fn+S): firmware toggles USBS before firing the event.
+ * The driver reads back the new state and notifies the sysfs attribute.
+ */
+
+/* USCS() return word bit layout */
+#define USCS_CAP_BIT		BIT(16)	/* capability: feature present on SKU */
+#define USCS_STATUS_BIT		BIT(0)	/* current security state */
+
+/* Protects USCS() ACPI method calls in usbc_security_query() */
+static DEFINE_MUTEX(usbc_security_mutex);
+
+/**
+ * usbc_security_query - read current USB-C security state via USCS()
+ * @enabled: out - true when security is ON (data connections blocked)
+ *
+ * Returns:
+ *   0        success, @enabled contains the current state
+ *  -EIO      ACPI evaluation failed
+ *  -ENODEV   capability bit absent; feature not present on this SKU*
+ */
+static int usbc_security_query(bool *enabled)
+{
+	int status;
+
+	guard(mutex)(&usbc_security_mutex);
+	if (!acpi_evalf(hkey_handle, &status, "USCS", "dd", 0))
+		return -EIO;
+
+	if (!(status & USCS_CAP_BIT)) {
+		pr_debug("USCS cap bit absent (raw=0x%x)\n", status);
+		return -ENODEV;
+	}
+
+	*enabled = status & USCS_STATUS_BIT;
+	return 0;
+}
+
+/* sysfs: /sys/devices/platform/thinkpad_acpi/usb_c_security ---------- */
+static ssize_t usb_c_security_show(struct device *dev,
+				   struct device_attribute *attr,
+				   char *buf)
+{
+	return sysfs_emit(buf, "%s\n",
+			  str_enabled_disabled(tp_features.usbc_security_enabled));
+}
+
+static DEVICE_ATTR_RO(usb_c_security);
+
+static struct attribute *usbc_security_attributes[] = {
+	&dev_attr_usb_c_security.attr,
+	NULL,
+};
+
+static umode_t usbc_security_attr_is_visible(struct kobject *kobj,
+					     struct attribute *attr, int n)
+{
+	return tp_features.usbc_security_supported ? attr->mode : 0;
+}
+
+static const struct attribute_group usbc_security_attr_group = {
+	.is_visible = usbc_security_attr_is_visible,
+	.attrs = usbc_security_attributes,
+};
+
+static int tpacpi_usbc_security_init(struct ibm_init_struct *iibm)
+{
+	int err;
+
+	err = usbc_security_query(&tp_features.usbc_security_enabled);
+	if (err == -ENODEV)
+		return 0;
+	if (err)
+		return err;
+
+	tp_features.usbc_security_supported = true;
+	return 0;
+}
+
+/* tpacpi_usbc_security_hotkey - handle Fn+U Fn+S hotkey (0x131e) */
+static bool tpacpi_usbc_security_hotkey(void)
+{
+	if (!tp_features.usbc_security_supported)
+		return false;
+
+	if (usbc_security_query(&tp_features.usbc_security_enabled))
+		return false;
+
+	sysfs_notify(&tpacpi_pdev->dev.kobj, NULL, "usb_c_security");
+	return true;
+}
+
+static struct ibm_struct usbc_security_driver_data = {
+	.name = "usbc_security",
+};
+
 /* --------------------------------------------------------------------- */
 
 static struct attribute *tpacpi_driver_attributes[] = {
@@ -11345,6 +11455,7 @@ static const struct attribute_group *tpacpi_groups[] = {
 	&dprc_attr_group,
 	&auxmac_attr_group,
 	&hwdd_attr_group,
+	&usbc_security_attr_group,
 	NULL,
 };
 
@@ -11499,6 +11610,8 @@ static bool tpacpi_driver_event(const unsigned int hkey_event)
 	case TP_HKEY_EV_PROFILE_TOGGLE2:
 		platform_profile_cycle();
 		return true;
+	case TP_HKEY_EV_USB_C_SECURITY:
+		return tpacpi_usbc_security_hotkey();
 	}
 
 	return false;
@@ -11964,6 +12077,10 @@ static struct ibm_init_struct ibms_init[] __initdata = {
 		.init = tpacpi_hwdd_init,
 		.data = &hwdd_driver_data,
 	},
+	{
+		.init = tpacpi_usbc_security_init,
+		.data = &usbc_security_driver_data,
+	},
 };
 
 static int __init set_ibm_param(const char *val, const struct kernel_param *kp)