Re: [PATCH 1/2] dt-bindings: input: goodix: Add powered-in-suspend property

From: Jeff LaBundy <jeff@labundy.com>
To: Fei Shao <fshao@chromium.org>
Cc: Benjamin Tissoires <benjamin.tissoires@redhat.com>,
	Douglas Anderson <dianders@chromium.org>,
	Rob Herring <robh+dt@kernel.org>,
	linux-mediatek <linux-mediatek@lists.infradead.org>,
	Dmitry Torokhov <dmitry.torokhov@gmail.com>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	devicetree@vger.kernel.org, linux-input@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] dt-bindings: input: goodix: Add powered-in-suspend property
Date: Tue, 18 Apr 2023 19:20:55 -0500	[thread overview]
Message-ID: <ZD8z57MBvcfExJx8@nixie71> (raw)
In-Reply-To: <20230418124953.3170028-2-fshao@chromium.org>

Hi Fei,

On Tue, Apr 18, 2023 at 08:49:51PM +0800, Fei Shao wrote:
> We observed that on Chromebook device Steelix, if Goodix GT7375P
> touchscreen is powered in suspend (because, for example, it connects to
> an always-on regulator) and with the reset GPIO asserted, it will
> introduce about 14mW power leakage.
> 
> This property is used to indicate that the touchscreen is powered in
> suspend. If it's set, the driver will stop asserting the reset GPIO in
> power-down, and it will do it in power-up instead to ensure that the
> state is always reset after resuming.
> 
> Signed-off-by: Fei Shao <fshao@chromium.org>
> ---

This is an interesting problem; were you able to root-cause why the silicon
exhibits this behavior? Simply asserting reset should not cause it to draw
additional power, let alone 14 mW. This almost sounds like a back-powering
problem during suspend.

If this is truly expected behavior, is it sufficient to use the always_on
constraint of the relevant regulator(s) to make this decision as opposed to
introducing a new property?

> 
>  Documentation/devicetree/bindings/input/goodix,gt7375p.yaml | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/input/goodix,gt7375p.yaml b/Documentation/devicetree/bindings/input/goodix,gt7375p.yaml
> index ce18d7dadae2..942acb286d77 100644
> --- a/Documentation/devicetree/bindings/input/goodix,gt7375p.yaml
> +++ b/Documentation/devicetree/bindings/input/goodix,gt7375p.yaml
> @@ -43,6 +43,12 @@ properties:
>        itself as long as it allows the main board to make signals compatible
>        with what the touchscreen is expecting for its IO rails.
>  
> +  powered-in-suspend:
> +    description:
> +      This indicates that the touchscreen is powered in suspend, so the driver
> +      will not assert the reset GPIO in power-down to prevent power leakage.
> +    type: boolean
> +
>  required:
>    - compatible
>    - reg
> -- 
> 2.40.0.634.g4ca3ef3211-goog
> 

Kind regards,
Jeff LaBundy