linux-kernel - Re: [PATCH] ARM: dts: imx6: skov: add pwm-regulator to control the panel's VCOM

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Message-ID: <6r8rpzwgiu.fsf@pengutronix.de>
Date:   Tue, 14 Jun 2022 14:53:58 +0200
From:   Ulrich Ölmann <u.oelmann@...gutronix.de>
To:     Shawn Guo <shawnguo@...nel.org>
Cc:     devicetree@...r.kernel.org,
        Michael Grzeschik <m.grzeschik@...gutronix.de>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Sam Ravnborg <sam@...nborg.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Juergen Borleis <jbe@...gutronix.de>,
        linux-kernel@...r.kernel.org,
        Marco Felsch <m.felsch@...gutronix.de>,
        Oleksij Rempel <o.rempel@...gutronix.de>,
        Rob Herring <robh+dt@...nel.org>,
        NXP Linux Team <linux-imx@....com>,
        Søren Andersen <san@...v.dk>,
        Fabio Estevam <festevam@...il.com>,
        Lucas Stach <l.stach@...gutronix.de>, kernel@...gutronix.de
Subject: Re: [PATCH] ARM: dts: imx6: skov: add pwm-regulator to control the
 panel's VCOM

On Sat, Jun 11 2022 at 17:31 +0800, Shawn Guo <shawnguo@...nel.org> wrote:
> On Tue, May 17, 2022 at 09:18:14AM +0200, Ulrich Ölmann wrote:
>> Skov's i.MX6 based boards come in different flavors which have different panels
>> attached. For optimal contrast experience each panel type needs an individual
>> common voltage (VCOM) to drive its TFT backplane. The latter is generated by an
>> LCD bias supply IC controlled by a pwm as input signal. Introduce a pwm-
>> regulator to describe this hardware property and parameterize it appropriately
>> for the different boards.
>>
>> Signed-off-by: Ulrich Ölmann <u.oelmann@...gutronix.de>
>> ---
>>  arch/arm/boot/dts/imx6q-skov-reve-mi1010ait-1cp1.dts |  6 ++++++
>>  arch/arm/boot/dts/imx6qdl-skov-cpu.dtsi              | 10 ++++++++++
>>  2 files changed, 16 insertions(+)
>>
>> diff --git a/arch/arm/boot/dts/imx6q-skov-reve-mi1010ait-1cp1.dts b/arch/arm/boot/dts/imx6q-skov-reve-mi1010ait-1cp1.dts
>> index 7f1f19b74bfa..a3f247c722b4 100644
>> --- a/arch/arm/boot/dts/imx6q-skov-reve-mi1010ait-1cp1.dts
>> +++ b/arch/arm/boot/dts/imx6q-skov-reve-mi1010ait-1cp1.dts
>> @@ -125,3 +125,9 @@ MX6QDL_PAD_EIM_D23__GPIO3_IO23		0x1b0b0
>>  		>;
>>  	};
>>  };
>> +
>> +&reg_tft_vcom {
>> +	regulator-min-microvolt = <3160000>;
>> +	regulator-max-microvolt = <3160000>;
>> +	voltage-table = <3160000 73>;
>> +};
>> diff --git a/arch/arm/boot/dts/imx6qdl-skov-cpu.dtsi b/arch/arm/boot/dts/imx6qdl-skov-cpu.dtsi
>> index 77a91a97e6cf..3def1b621c8e 100644
>> --- a/arch/arm/boot/dts/imx6qdl-skov-cpu.dtsi
>> +++ b/arch/arm/boot/dts/imx6qdl-skov-cpu.dtsi
>> @@ -149,6 +149,16 @@ reg_can2_stby: regulator-can2-stby {
>>  		gpio = <&gpio4 11 GPIO_ACTIVE_LOW>;
>>  	};
>>
>> +	reg_tft_vcom: regulator-tft-vcom {
>> +		compatible = "pwm-regulator";
>> +		pwms = <&pwm3 0 20000 0>;
>> +		regulator-name = "tft_vcom";
>> +		regulator-min-microvolt = <3600000>;
>> +		regulator-max-microvolt = <3600000>;
>> +		regulator-always-on;
>
> You want it to be unmanaged and always-on?

Correct, it shall be set up by the kernel statically and is never going
to be changed while the system is up and running.

Best regards
Ulrich


> Shawn
>
>> +		voltage-table = <3600000 26>;
>> +	};
>> +
>>  	reg_vcc_mmc: regulator-vcc-mmc {
>>  		compatible = "regulator-fixed";
>>  		pinctrl-names = "default";
>> --
>> 2.30.2
>>
-- 
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