Hi,

On Sat, Feb 28, 2026 at 03:52:58PM +0100, Hans de Goede wrote:
> Elan touchscreens have a HID-battery device for the stylus which is always
> there even if there is no stylus.
> 
> This is causing upower to report an empty battery for the stylus and some
> desktop-environments will show a notification about this, which is quite
> annoying.
> 
> Because of this the HID-battery is being ignored on all Elan I2c and USB
> touchscreens, but this causes there to be no battery reporting for
> the stylus at all.
> 
> This adds a new HID_BATTERY_QUIRK_DYNAMIC and uses these for the Elan
> touchscreens.
> 
> This new quirks causes the present value of the battery to start at 0,
> which will make userspace ignore it and only sets present to 1 after
> receiving a battery input report which only happens when the stylus
> gets in range.
> 
> Reported-by: ggrundik@gmail.com
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=221118
> Signed-off-by: Hans de Goede <johannes.goede@oss.qualcomm.com>
> ---

Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>

-- Sebastian

>  drivers/hid/hid-input.c | 14 +++++++++++---
>  include/linux/hid.h     |  1 +
>  2 files changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/hid/hid-input.c b/drivers/hid/hid-input.c
> index 67ca1e88ce13..8fc20df99b97 100644
> --- a/drivers/hid/hid-input.c
> +++ b/drivers/hid/hid-input.c
> @@ -354,6 +354,7 @@ static enum power_supply_property hidinput_battery_props[] = {
>  #define HID_BATTERY_QUIRK_FEATURE	(1 << 1) /* ask for feature report */
>  #define HID_BATTERY_QUIRK_IGNORE	(1 << 2) /* completely ignore the battery */
>  #define HID_BATTERY_QUIRK_AVOID_QUERY	(1 << 3) /* do not query the battery */
> +#define HID_BATTERY_QUIRK_DYNAMIC	(1 << 4) /* report present only after life signs */
>  
>  static const struct hid_device_id hid_battery_quirks[] = {
>  	{ HID_BLUETOOTH_DEVICE(USB_VENDOR_ID_APPLE,
> @@ -398,8 +399,8 @@ static const struct hid_device_id hid_battery_quirks[] = {
>  	 * Elan HID touchscreens seem to all report a non present battery,
>  	 * set HID_BATTERY_QUIRK_IGNORE for all Elan I2C and USB HID devices.
>  	 */
> -	{ HID_I2C_DEVICE(USB_VENDOR_ID_ELAN, HID_ANY_ID), HID_BATTERY_QUIRK_IGNORE },
> -	{ HID_USB_DEVICE(USB_VENDOR_ID_ELAN, HID_ANY_ID), HID_BATTERY_QUIRK_IGNORE },
> +	{ HID_I2C_DEVICE(USB_VENDOR_ID_ELAN, HID_ANY_ID), HID_BATTERY_QUIRK_DYNAMIC },
> +	{ HID_USB_DEVICE(USB_VENDOR_ID_ELAN, HID_ANY_ID), HID_BATTERY_QUIRK_DYNAMIC },
>  	{}
>  };
>  
> @@ -456,11 +457,14 @@ static int hidinput_get_battery_property(struct power_supply *psy,
>  	int ret = 0;
>  
>  	switch (prop) {
> -	case POWER_SUPPLY_PROP_PRESENT:
>  	case POWER_SUPPLY_PROP_ONLINE:
>  		val->intval = 1;
>  		break;
>  
> +	case POWER_SUPPLY_PROP_PRESENT:
> +		val->intval = dev->battery_present;
> +		break;
> +
>  	case POWER_SUPPLY_PROP_CAPACITY:
>  		if (dev->battery_status != HID_BATTERY_REPORTED &&
>  		    !dev->battery_avoid_query) {
> @@ -573,6 +577,8 @@ static int hidinput_setup_battery(struct hid_device *dev, unsigned report_type,
>  	if (quirks & HID_BATTERY_QUIRK_AVOID_QUERY)
>  		dev->battery_avoid_query = true;
>  
> +	dev->battery_present = (quirks & HID_BATTERY_QUIRK_DYNAMIC) ? false : true;
> +
>  	dev->battery = power_supply_register(&dev->dev, psy_desc, &psy_cfg);
>  	if (IS_ERR(dev->battery)) {
>  		error = PTR_ERR(dev->battery);
> @@ -628,6 +634,7 @@ static void hidinput_update_battery(struct hid_device *dev, unsigned int usage,
>  		return;
>  
>  	if (hidinput_update_battery_charge_status(dev, usage, value)) {
> +		dev->battery_present = true;
>  		power_supply_changed(dev->battery);
>  		return;
>  	}
> @@ -643,6 +650,7 @@ static void hidinput_update_battery(struct hid_device *dev, unsigned int usage,
>  	if (dev->battery_status != HID_BATTERY_REPORTED ||
>  	    capacity != dev->battery_capacity ||
>  	    ktime_after(ktime_get_coarse(), dev->battery_ratelimit_time)) {
> +		dev->battery_present = true;
>  		dev->battery_capacity = capacity;
>  		dev->battery_status = HID_BATTERY_REPORTED;
>  		dev->battery_ratelimit_time =
> diff --git a/include/linux/hid.h b/include/linux/hid.h
> index dce862cafbbd..d9b54f0e8671 100644
> --- a/include/linux/hid.h
> +++ b/include/linux/hid.h
> @@ -682,6 +682,7 @@ struct hid_device {
>  	__s32 battery_charge_status;
>  	enum hid_battery_status battery_status;
>  	bool battery_avoid_query;
> +	bool battery_present;
>  	ktime_t battery_ratelimit_time;
>  #endif
>  
> -- 
> 2.52.0