On Thu, 28 May 2026, Dariusz Figzał wrote:

> The ASUS Keystone is a physical NFC-like dongle that slots into supported
> ASUS laptops. The EC fires WMI notify code 0xB4 on insert/remove events.
> 
> Expose the current insert state via a sysfs attribute by querying WMI
> device ID 0x00120091 (DSTS). This devid does not follow the standard DSTS
> convention: PRESENCE_BIT (0x00010000) encodes the insert state rather than
> feature presence, and STATUS_BIT is never set. Presence of a keystone slot
> is detected by a successful DSTS call.
> 
> Signed-off-by: Dariusz Figzał <dariuszfigzal@gmail.com>
> ---
> 
> Changes in v2:
> - Use .is_visible and platform_attributes[] instead of
>   device_create_file/device_remove_file (Ilpo Järvinen)
> 
>  drivers/platform/x86/asus-wmi.c            | 65 ++++++++++++++++++++++
>  include/linux/platform_data/x86/asus-wmi.h |  7 +++

Please document the interface in
Documentation/ABI/testing/sysfs-platform-asus-wmi

--
 i.

>  2 files changed, 72 insertions(+)
> 
> diff --git a/drivers/platform/x86/asus-wmi.c b/drivers/platform/x86/asus-wmi.c
> index 80144c412b90..3c9ef826551d 100644
> --- a/drivers/platform/x86/asus-wmi.c
> +++ b/drivers/platform/x86/asus-wmi.c
> @@ -70,6 +70,7 @@ module_param(fnlock_default, bool, 0444);
>  #define NOTIFY_KBD_TTP			0xae
>  #define NOTIFY_LID_FLIP			0xfa
>  #define NOTIFY_LID_FLIP_ROG		0xbd
> +#define NOTIFY_KEYSTONE			0xb4
>  
>  #define ASUS_WMI_FNLOCK_BIOS_DISABLED	BIT(0)
>  
> @@ -279,6 +280,8 @@ struct asus_wmi {
>  	u32 tablet_switch_dev_id;
>  	bool tablet_switch_inverted;
>  
> +	bool keystone_available;
> +
>  	enum fan_type fan_type;
>  	enum fan_type gpu_fan_type;
>  	enum fan_type mid_fan_type;
> @@ -646,6 +649,55 @@ static bool asus_wmi_dev_is_present(struct asus_wmi *asus, u32 dev_id)
>  	return status == 0 && (retval & ASUS_WMI_DSTS_PRESENCE_BIT);
>  }
>  
> +/* Keystone *******************************************************************/
> +
> +static int keystone_check_present(struct asus_wmi *asus)
> +{
> +	u32 retval;
> +	int err;
> +
> +	asus->keystone_available = false;
> +
> +	/*
> +	 * Use a raw devstate call rather than asus_wmi_dev_is_present().
> +	 * For this devid, PRESENCE_BIT encodes current insert state, not
> +	 * feature presence, so asus_wmi_dev_is_present() would return false
> +	 * whenever the dongle is absent at boot, even on machines that have
> +	 * a keystone slot.
> +	 * -ENODEV means the firmware doesn't know this devid at all.
> +	 * retval is not examined here, only the return code matters.
> +	 */
> +	err = asus_wmi_get_devstate(asus, ASUS_WMI_DEVID_KEYSTONE, &retval);
> +	if (err == -ENODEV)
> +		return 0;
> +	if (err)
> +		return err;
> +
> +	asus->keystone_available = true;
> +	return 0;
> +}
> +
> +static ssize_t keystone_show(struct device *dev,
> +			     struct device_attribute *attr, char *buf)
> +{
> +	struct asus_wmi *asus = dev_get_drvdata(dev);
> +	u32 retval;
> +	int err;
> +
> +	err = asus_wmi_get_devstate(asus, ASUS_WMI_DEVID_KEYSTONE, &retval);
> +	if (err)
> +		return err;
> +
> +	return sysfs_emit(buf, "%d\n", !!(retval & ASUS_WMI_DSTS_PRESENCE_BIT));
> +}
> +
> +static DEVICE_ATTR_RO(keystone);
> +
> +static void asus_wmi_keystone_notify(struct asus_wmi *asus)
> +{
> +	sysfs_notify(&asus->platform_device->dev.kobj, NULL, "keystone");
> +}
> +
>  /* Input **********************************************************************/
>  static void asus_wmi_tablet_sw_report(struct asus_wmi *asus, bool value)
>  {
> @@ -4575,6 +4627,12 @@ static void asus_wmi_handle_event_code(int code, struct asus_wmi *asus)
>  		return;
>  	}
>  
> +	if (code == NOTIFY_KEYSTONE) {
> +		if (asus->keystone_available)
> +			asus_wmi_keystone_notify(asus);
> +		return;
> +	}
> +
>  	if (code == NOTIFY_KBD_FBM || code == NOTIFY_KBD_TTP) {
>  		if (asus->fan_boost_mode_available)
>  			fan_boost_mode_switch_next(asus);
> @@ -4698,6 +4756,7 @@ static struct attribute *platform_attributes[] = {
>  	&dev_attr_lid_resume.attr,
>  	&dev_attr_als_enable.attr,
>  	&dev_attr_fan_boost_mode.attr,
> +	&dev_attr_keystone.attr,
>  #if IS_ENABLED(CONFIG_ASUS_WMI_DEPRECATED_ATTRS)
>  		&dev_attr_charge_mode.attr,
>  		&dev_attr_egpu_enable.attr,
> @@ -4741,6 +4800,8 @@ static umode_t asus_sysfs_is_visible(struct kobject *kobj,
>  		devid = ASUS_WMI_DEVID_ALS_ENABLE;
>  	else if (attr == &dev_attr_fan_boost_mode.attr)
>  		ok = asus->fan_boost_mode_available;
> +	else if (attr == &dev_attr_keystone.attr)
> +		ok = asus->keystone_available;
>  
>  #if IS_ENABLED(CONFIG_ASUS_WMI_DEPRECATED_ATTRS)
>  	if (attr == &dev_attr_charge_mode.attr)
> @@ -5081,6 +5142,10 @@ static int asus_wmi_add(struct platform_device *pdev)
>  	if (err)
>  		goto fail_platform_profile_setup;
>  
> +	err = keystone_check_present(asus);
> +	if (err)
> +		dev_warn(&pdev->dev, "Failed to check Keystone presence: %d\n", err);
> +
>  	err = asus_wmi_sysfs_init(asus->platform_device);
>  	if (err)
>  		goto fail_sysfs;
> diff --git a/include/linux/platform_data/x86/asus-wmi.h b/include/linux/platform_data/x86/asus-wmi.h
> index 554f41b827e1..c29962d5baac 100644
> --- a/include/linux/platform_data/x86/asus-wmi.h
> +++ b/include/linux/platform_data/x86/asus-wmi.h
> @@ -147,6 +147,13 @@
>  #define ASUS_WMI_DEVID_GPU_MUX		0x00090016
>  #define ASUS_WMI_DEVID_GPU_MUX_VIVO	0x00090026
>  
> +/* Keystone dongle insert/remove state.
> + * PRESENCE_BIT (0x00010000) encodes insert state:
> + * 0x00010000 = inserted, 0x00000000 = absent. STATUS_BIT is never set.
> + * 0xFFFFFFFE means no keystone slot on this machine.
> + */
> +#define ASUS_WMI_DEVID_KEYSTONE		0x00120091
> +
>  /* TUF laptop RGB modes/colours */
>  #define ASUS_WMI_DEVID_TUF_RGB_MODE	0x00100056
>  #define ASUS_WMI_DEVID_TUF_RGB_MODE2	0x0010005A
>