Re: [PATCH] platform/x86: thinkpad-acpi: Add X1 Fold keyboard attachment detection

[Hans de Goede <hansg@kernel.org>]

Hi,

On 14-Mar-26 7:24 PM, Mark Pearson wrote:
> Hi Pit,
> 
> On Sat, Mar 14, 2026, at 10:22 AM, Pit Henrich wrote:
>> ThinkPad X1 Fold 16 Gen 1 firmware reports whether the keyboard is magnetically
>> attached (on the screen) via EC register 0xc1 bit 7, but thinkpad-acpi does
>> not expose this to userspace.
>>
>> Add a read-only keyboard_attached_on_screen sysfs attribute, gated by
>> a DMI match. The state is read directly from the EC.
>>
>> Cache the state and emit a sysfs notification on
>> TP_HKEY_EV_TABLET_CHANGED (0x60c0) when it changes. Initialize the cache during
>> hotkey setup and refresh it before the resume notification to keep the state
>> consistent across suspend and resume.
>>
>> Signed-off-by: Pit Henrich <pithenrich2d@gmail.com>
>> ---
>>  drivers/platform/x86/lenovo/thinkpad_acpi.c | 92 ++++++++++++++++++++-
>>  1 file changed, 90 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/platform/x86/lenovo/thinkpad_acpi.c 
>> b/drivers/platform/x86/lenovo/thinkpad_acpi.c
>> index 8982d92dfd97..5b255062ff51 100644
>> --- a/drivers/platform/x86/lenovo/thinkpad_acpi.c
>> +++ b/drivers/platform/x86/lenovo/thinkpad_acpi.c
>> @@ -218,8 +218,9 @@ enum tpacpi_hkey_event_t {
>>  	TP_HKEY_EV_LID_OPEN		= 0x5002, /* laptop lid opened */
>>  	TP_HKEY_EV_TABLET_TABLET	= 0x5009, /* tablet swivel up */
>>  	TP_HKEY_EV_TABLET_NOTEBOOK	= 0x500a, /* tablet swivel down */
>> -	TP_HKEY_EV_TABLET_CHANGED	= 0x60c0, /* X1 Yoga (2016):
>> -						   * enter/leave tablet mode
>> +	TP_HKEY_EV_TABLET_CHANGED	= 0x60c0, /* posture change event:
>> +						   * X1 Yoga (2016): enter/leave tablet mode
>> +						   * X1 Fold 16 Gen 1: keyboard attachment state changed
>>  						   */
>>  	TP_HKEY_EV_PEN_INSERTED		= 0x500b, /* tablet pen inserted */
>>  	TP_HKEY_EV_PEN_REMOVED		= 0x500c, /* tablet pen removed */
>> @@ -375,6 +376,7 @@ static struct {
>>  	u32 has_adaptive_kbd:1;
>>  	u32 kbd_lang:1;
>>  	u32 trackpoint_doubletap:1;
>> +	u32 has_keyboard_attached_on_screen:1;
>>  	struct quirk_entry *quirks;
>>  } tp_features;
>>
>> @@ -2928,6 +2930,70 @@ static void hotkey_tablet_mode_notify_change(void)
>>  			     "hotkey_tablet_mode");
>>  }
>>
>> +/*
>> + * On the ThinkPad X1 Fold 16 Gen 1, EC register 0xc1 reports the 
>> keyboard
>> + * attachment state in bit 7.
>> + */
>> +#define TPACPI_X1_FOLD_KBD_EC_STATUS	0xc1
>> +#define TPACPI_X1_FOLD_KBD_ATTACHED	BIT(7)
>> +
>> +static bool keyboard_attached_on_screen;
>> +static bool keyboard_attached_on_screen_initialized;
>> +
>> +static int x1_fold_keyboard_attached_on_screen_get(bool *attached)
>> +{
>> +	u8 status;
>> +
>> +	if (!tp_features.has_keyboard_attached_on_screen)
>> +		return -ENODEV;
>> +
>> +	if (!acpi_ec_read(TPACPI_X1_FOLD_KBD_EC_STATUS, &status))
>> +		return -EIO;
>> +
>> +	*attached = status & TPACPI_X1_FOLD_KBD_ATTACHED;
>> +	return 0;
>> +}
>> +
>> +static ssize_t keyboard_attached_on_screen_show(struct device *dev,
>> +						struct device_attribute *attr,
>> +						char *buf)
>> +{
>> +	bool attached;
>> +	int res;
>> +
>> +	res = x1_fold_keyboard_attached_on_screen_get(&attached);
>> +	if (res)
>> +		return res;
>> +
>> +	return sysfs_emit(buf, "%d\n", attached);
>> +}
>> +
>> +static DEVICE_ATTR_RO(keyboard_attached_on_screen);
>> +
>> +static void keyboard_attached_on_screen_notify_change(void)
>> +{
>> +	if (tp_features.has_keyboard_attached_on_screen)
>> +		sysfs_notify(&tpacpi_pdev->dev.kobj, NULL,
>> +			     "keyboard_attached_on_screen");
>> +}
>> +
>> +static bool keyboard_attached_on_screen_update(void)
>> +{
>> +	bool attached;
>> +
>> +	if (x1_fold_keyboard_attached_on_screen_get(&attached))
>> +		return false;
>> +
>> +	if (keyboard_attached_on_screen_initialized &&
>> +	    keyboard_attached_on_screen == attached)
>> +		return false;
>> +
>> +	keyboard_attached_on_screen = attached;
>> +	keyboard_attached_on_screen_initialized = true;
>> +
>> +	return true;
>> +}
>> +
>>  /* sysfs wakeup reason (pollable) 
>> -------------------------------------- */
>>  static ssize_t hotkey_wakeup_reason_show(struct device *dev,
>>  			   struct device_attribute *attr,
>> @@ -3032,6 +3098,7 @@ static struct attribute *hotkey_attributes[] = {
>>  	&dev_attr_hotkey_adaptive_all_mask.attr,
>>  	&dev_attr_hotkey_recommended_mask.attr,
>>  	&dev_attr_hotkey_tablet_mode.attr,
>> +	&dev_attr_keyboard_attached_on_screen.attr,
>>  	&dev_attr_hotkey_radio_sw.attr,
>>  #ifdef CONFIG_THINKPAD_ACPI_HOTKEY_POLL
>>  	&dev_attr_hotkey_source_mask.attr,
>> @@ -3046,6 +3113,9 @@ static umode_t hotkey_attr_is_visible(struct 
>> kobject *kobj,
>>  	if (attr == &dev_attr_hotkey_tablet_mode.attr) {
>>  		if (!tp_features.hotkey_tablet)
>>  			return 0;
>> +	} else if (attr == &dev_attr_keyboard_attached_on_screen.attr) {
>> +		if (!tp_features.has_keyboard_attached_on_screen)
>> +			return 0;
>>  	} else if (attr == &dev_attr_hotkey_radio_sw.attr) {
>>  		if (!tp_features.hotkey_wlsw)
>>  			return 0;
>> @@ -3462,6 +3532,7 @@ static int __init hotkey_init(struct 
>> ibm_init_struct *iibm)
>>  	}
>>
>>  	tabletsw_state = hotkey_init_tablet_mode();
>> +	keyboard_attached_on_screen_update();
>>
>>  	/* Set up key map */
>>  	keymap_id = tpacpi_check_quirks(tpacpi_keymap_qtable,
>> @@ -3842,6 +3913,8 @@ static bool hotkey_notify_6xxx(const u32 hkey, 
>> bool *send_acpi_ev)
>>  	case TP_HKEY_EV_TABLET_CHANGED:
>>  		tpacpi_input_send_tabletsw();
>>  		hotkey_tablet_mode_notify_change();
>> +		if (keyboard_attached_on_screen_update())
>> +			keyboard_attached_on_screen_notify_change();
>>  		*send_acpi_ev = false;
>>  		return true;
>>
>> @@ -3998,6 +4071,8 @@ static void hotkey_resume(void)
>>  	tpacpi_send_radiosw_update();
>>  	tpacpi_input_send_tabletsw();
>>  	hotkey_tablet_mode_notify_change();
>> +	keyboard_attached_on_screen_update();
>> +	keyboard_attached_on_screen_notify_change();
>>  	hotkey_wakeup_reason_notify_change();
>>  	hotkey_wakeup_hotunplug_complete_notify_change();
>>  	hotkey_poll_setup_safe(false);
>> @@ -4296,6 +4371,17 @@ static const struct dmi_system_id fwbug_list[] 
>> __initconst = {
>>  	{}
>>  };
>>
>> +static const struct dmi_system_id keyboard_attached_on_screen_list[] 
>> __initconst = {
>> +	{
>> +		.ident = "ThinkPad X1 Fold 16 Gen 1",
>> +		.matches = {
>> +			DMI_MATCH(DMI_SYS_VENDOR, "LENOVO"),
>> +			DMI_MATCH(DMI_PRODUCT_FAMILY, "ThinkPad X1 Fold 16 Gen 1"),
>> +		},
>> +	},
>> +	{}
>> +};
>> +
>>  static const struct pci_device_id fwbug_cards_ids[] __initconst = {
>>  	{ PCI_DEVICE(PCI_VENDOR_ID_INTEL, 0x24F3) },
>>  	{ PCI_DEVICE(PCI_VENDOR_ID_INTEL, 0x24FD) },
>> @@ -12230,6 +12316,8 @@ static int __init 
>> thinkpad_acpi_module_init(void)
>>  	dmi_id = dmi_first_match(fwbug_list);
>>  	if (dmi_id)
>>  		tp_features.quirks = dmi_id->driver_data;
>> +	tp_features.has_keyboard_attached_on_screen =
>> +		dmi_check_system(keyboard_attached_on_screen_list);
>>
>>  	/* Device initialization */
>>  	tpacpi_pdev = platform_device_register_simple(TPACPI_DRVR_NAME, 
>> PLATFORM_DEVID_NONE,
>> -- 
>> 2.43.0
> 
> I'm checking to see if we have the EC spec for this platform (it's not in our Linux certification program).
> 
> The code looks fine but some notes:
>  - We usually do the DMI_MATCH on the BOARD_NAME for quirks. I was checking psref.lenovo.com and there seem to be two distinct models for this platform, which is a bit confusing. I don't have a way to confirm that your changes will work for the other model so wondering if it's safer to do the quirks for 21ES/21ET or 20RL/20RK depending on what you have in hand? (I might be overthinking this too)
>  - I would have called it detachable_keyboard instead of keyboard_attached_on_screen. See what other reviewers think.

Looking at pictures of the Fold 16 gen 1, I assume this sysfs attr will return 1 when the keyboard
is clicked on one half of the foldable screen, covering that half so that the laptop resembles
a classic clamshell design in this mode. Since this is actually covering half the screen I think
that keyboard_attached_on_screen actually is a good name :)

Regards,

Hans