linux-kernel - Re: [PATCH 1/3] arm64: dts: mediatek: asurada: Add display regulators

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Message-ID: <9234e731-8c2f-b599-39b1-bf5115a16931@collabora.com>
Date:   Wed, 21 Sep 2022 15:58:46 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Nícolas F. R. A. Prado 
        <nfraprado@...labora.com>
Cc:     Matthias Brugger <matthias.bgg@...il.com>,
        Chen-Yu Tsai <wenst@...omium.org>, kernel@...labora.com,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH 1/3] arm64: dts: mediatek: asurada: Add display regulators

Il 21/09/22 15:48, Nícolas F. R. A. Prado ha scritto:
> On Fri, Sep 09, 2022 at 09:46:33AM +0200, AngeloGioacchino Del Regno wrote:
>> Il 08/09/22 19:11, Nícolas F. R. A. Prado ha scritto:
>>> Add the regulators present on the Asurada platform that are used to
>>> power the internal and external displays.
>>>
>>> Signed-off-by: Nícolas F. R. A. Prado <nfraprado@...labora.com>
>>>
>>> ---
>>>
>>>    .../boot/dts/mediatek/mt8192-asurada.dtsi     | 114 ++++++++++++++++++
>>>    1 file changed, 114 insertions(+)
>>>
>>> diff --git a/arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi b/arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi
>>> index 4b314435f8fd..1d99e470ea1a 100644
>>> --- a/arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi
>>> +++ b/arch/arm64/boot/dts/mediatek/mt8192-asurada.dtsi
>>
>> ..snip..
>>
>>> @@ -56,6 +116,18 @@ pp3300_ldo_z: regulator-3v3-z {
>>>    		vin-supply = <&ppvar_sys>;
>>>    	};
>>
>> Can you please add a comment here advertising that this regulator
>> will not only provide power to the MIPI bridge, but *also* to the
>> display panel itself?
>>
>> This is to make sure that everyone understands what's going on, and
>> also that we ourselves don't forget about that.
>>
>> Probably something like:
>> /* pp3300_mipibrdg also enables pp3300_panel */
>>
>> I would then propose to add a "regulator-fixed" that has no GPIO
>> but with vin-supply as this one.
>>
>> pp3300_panel: regulator-3v3-panel {
>> 	compatible = "regulator-fixed";
>> 	regulator-name = "pp3300_panel";
>> 	regulator-min-microvolt = <3300000>;
>> 	regulator-max-microvolt = <3300000>;
>>
>> 	vin-supply = <&pp3300_mipibrdg>;
>> };
>>
>> I would also test assigning this regulator to the panel node, as this
>> will make sure to cover future corner cases (think about PM suspend/resume).
>>
>> P.S.: If you add the pp3300_panel regulator-fixed with that vin-supply,
>>        maybe the proposed comment would become a bit overkill. Your choice!
> 
> Hi Angelo,
> 
> thanks for the feedback.
> 
> I think the current layout makes more sense based on my understanding of the
> power routing here: a single power line output by the pp3300_mipibrdg regulator
> powers both the ANX chip as well as the panel. So I'm going to keep it the way
> it is for now. If there are any other concerns please let me know.
> 

As we discussed, I agree on this decision. Please go on.

Cheers!

> Thanks,
> Nícolas
> 
>>
>> Cheers,
>> Angelo
>>
>>> +	pp3300_mipibrdg: regulator-3v3-mipibrdg {
>>> +		compatible = "regulator-fixed";
>>> +		regulator-name = "pp3300_mipibrdg";
>>> +		pinctrl-names = "default";
>>> +		pinctrl-0 = <&pp3300_mipibrdg_en_pins>;
>>> +		regulator-min-microvolt = <3300000>;
>>> +		regulator-max-microvolt = <3300000>;
>>> +		enable-active-high;
>>> +		regulator-boot-on;
>>> +		gpio = <&pio 127 GPIO_ACTIVE_HIGH>;
>>> +	};
>>> +
>>>    	/* separately switched 3.3V power rail */
>>>    	pp3300_u: regulator-3v3-u {
>>>    		compatible = "regulator-fixed";
>>