Re: [PATCH v3 2/2] arm64: dts: qcom: sc8280xp-x13s: Fix/enable touchscreen

[Rob Herring <robh@kernel.org>]

On Mon, Jan 29, 2024 at 08:47:48AM -0800, Bjorn Andersson wrote:
> The touchscreen present on some SKUs of Lenovo Thinkpad X13s is never
> detected by Linux. Power is applied and the device is brought out of
> reset using the pinconfig in DeviceTree, but the read-test in
> __i2c_hid_core_probe() fails to access the device, which result in probe
> being aborted.
> 
> Some users have reported success after rebinding the device.
> 
> Looking to the ACPI tables, there's a 5ms after-power and a 200ms
> after-reset delay. The power-supply is shared with other components, so
> this is active all the way through boot. The reset GPIO, on the other
> hand, is low (reset asserted) at boot, so this is first deasserted by
> the implicit application of the pinconf state.
> 
> This means the time between reset deassert and __i2c_hid_core_probe() is
> significantly below the value documented in the ACPI tables.
> 
> As the I2C HID binding and driver support specifying a reset gpio,
> replace the pinconf-based scheme to pull the device out of reset. Then
> specify the after-reset time.
> 
> The shared power rail is currently always on, but in case this ever
> change, the after-power delay is added as well, to not violate the
> power-on to reset-deassert timing requirement.
> 
> Fixes: 32c231385ed4 ("arm64: dts: qcom: sc8280xp: add Lenovo Thinkpad X13s devicetree")
> Tested-by: Daniel Thompson <daniel.thompson@linaro.org>
> Signed-off-by: Bjorn Andersson <quic_bjorande@quicinc.com>
> ---
>  arch/arm64/boot/dts/qcom/sc8280xp-lenovo-thinkpad-x13s.dts | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/boot/dts/qcom/sc8280xp-lenovo-thinkpad-x13s.dts b/arch/arm64/boot/dts/qcom/sc8280xp-lenovo-thinkpad-x13s.dts
> index def3976bd5bb..33731b95ad51 100644
> --- a/arch/arm64/boot/dts/qcom/sc8280xp-lenovo-thinkpad-x13s.dts
> +++ b/arch/arm64/boot/dts/qcom/sc8280xp-lenovo-thinkpad-x13s.dts
> @@ -620,7 +620,6 @@ &i2c4 {
>  
>  	status = "okay";
>  
> -	/* FIXME: verify */
>  	touchscreen@10 {
>  		compatible = "hid-over-i2c";

Please add a real device compatible before you need the next power 
sequencing property I'll reject.

>  		reg = <0x10>;
> @@ -630,6 +629,11 @@ touchscreen@10 {
>  		vdd-supply = <&vreg_misc_3p3>;
>  		vddl-supply = <&vreg_s10b>;
>  
> +		reset-gpios = <&tlmm 99 GPIO_ACTIVE_LOW>;
> +
> +		post-power-on-delay-ms = <5>;
> +		post-reset-deassert-delay-ms = <200>;
> +
>  		pinctrl-names = "default";
>  		pinctrl-0 = <&ts0_default>;
>  	};
> @@ -1450,7 +1454,6 @@ int-n-pins {
>  		reset-n-pins {
>  			pins = "gpio99";
>  			function = "gpio";
> -			output-high;
>  			drive-strength = <16>;
>  		};
>  	};
> 
> -- 
> 2.25.1
>