Hi,

On Wed, Aug 04, 2021 at 07:02:00PM +0800, Ting Wang wrote:
> From: wangting11 <wangting11@xiaomi.com>
> 
> reports wireless signal strength.
> The value show degree of coupling between tx and rx.
> 
> Signed-off-by: wangting11 <wangting11@xiaomi.com>
> ---

You also need a user for this property.

>  Documentation/ABI/testing/sysfs-class-power | 22 +++++++++++++++++++++
>  drivers/power/supply/power_supply_sysfs.c   |  1 +
>  include/linux/power_supply.h                |  1 +
>  3 files changed, 24 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-class-power b/Documentation/ABI/testing/sysfs-class-power
> index 36808bf8731b..4a6b4970cb7d 100644
> --- a/Documentation/ABI/testing/sysfs-class-power
> +++ b/Documentation/ABI/testing/sysfs-class-power
> @@ -785,3 +785,25 @@ Description:
>  			13: ADAPTER_VOICE_BOX,
>  			14: ADAPTER_PRIVATE_PD_50W.
>  
> +What:		/sys/class/power_supply/<supply_name>/signal_strength
> +Date:		Jul 2020
> +Contact:	Fei Jiang <jiangfei1@xiaomi.com>
> +Description:
> +		In PING phase, RX transmits a signal strength packet as the
> +		first communication packet to instruct the base to keep power
> +		signal on.The value reports wireless signal strength and show
> +		degree of coupling.
> +
> +		The Qi Wireless Power Transfer System is published by the
> +		Wireless Power Consortium.The ping phase is the necessary stage
> +		for matching transmitter and receiver. In this phase,the Power
> +		Transmitter executes a Digital Ping, and listens for a response.
> +		If the Power Transmitter discovers a Power Receiver, the Power
> +		Transmitter may extend the Digital Ping,i.e. maintain the Power
> +		Signal at the level of the Digital Ping. This causes the system
> +		to proceed to the identification & configuration phase. If the
> +		Power Transmitter does not extend the Digital Ping, the system
> +		shall revert to the selection phase.

A lot of text, but not much information what 'signal_strength' reports.
IIUIC it could be rephrased like this simple sentence?

Reports the degree coupling between wireless RX and TX side of a
wireless charger in %.

-- Sebastian

> +		Access: Read-Only
> +		Valid values: 0 - 100
> diff --git a/drivers/power/supply/power_supply_sysfs.c b/drivers/power/supply/power_supply_sysfs.c
> index 561cffef9d61..4de91dce2001 100644
> --- a/drivers/power/supply/power_supply_sysfs.c
> +++ b/drivers/power/supply/power_supply_sysfs.c
> @@ -213,6 +213,7 @@ static struct power_supply_attr power_supply_attrs[] = {
>  	POWER_SUPPLY_ATTR(SERIAL_NUMBER),
>  	POWER_SUPPLY_ATTR(QUICK_CHARGE_TYPE),
>  	POWER_SUPPLY_ATTR(TX_ADAPTER),
> +	POWER_SUPPLY_ATTR(SIGNAL_STRENGTH),
>  };
>  
>  static struct attribute *
> diff --git a/include/linux/power_supply.h b/include/linux/power_supply.h
> index bcfadf2a995f..0dfec19cb473 100644
> --- a/include/linux/power_supply.h
> +++ b/include/linux/power_supply.h
> @@ -173,6 +173,7 @@ enum power_supply_property {
>  	POWER_SUPPLY_PROP_SERIAL_NUMBER,
>  	POWER_SUPPLY_PROP_QUICK_CHARGE_TYPE,
>  	POWER_SUPPLY_PROP_TX_ADAPTER,
> +	POWER_SUPPLY_PROP_SIGNAL_STRENGTH,
>  };
>  
>  enum power_supply_type {
> -- 
> 2.17.1
>