linux-kernel - Re: [PATCH 1/4] arm64: dts: mediatek: mt8183-kukui-jacuzzi: Drop pp3300

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Message-ID: <bbaa0c8f-9702-4252-a674-e46fb51f0a2a@collabora.com>
Date: Mon, 4 Nov 2024 14:19:09 +0100
From: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
To: Chen-Yu Tsai <wenst@...omium.org>,
 Matthias Brugger <matthias.bgg@...il.com>
Cc: devicetree@...r.kernel.org, linux-mediatek@...ts.infradead.org,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] arm64: dts: mediatek: mt8183-kukui-jacuzzi: Drop
 pp3300_panel voltage settings

Il 04/11/24 14:00, Chen-Yu Tsai ha scritto:
> On Wed, Oct 30, 2024 at 3:02 PM Chen-Yu Tsai <wenst@...omium.org> wrote:
>>
>> The pp3300_panel fixed regulator is just a load switch. It does not have
>> any regulating capabilities. Thus having voltage constraints on it is
>> wrong.
>>
>> Remove the voltage constraints.
>>
>> Fixes: cabc71b08eb5 ("arm64: dts: mt8183: Add kukui-jacuzzi-damu board")
>> Signed-off-by: Chen-Yu Tsai <wenst@...omium.org>
> 
> I see that the other three patches were merged and included in the pull
> request, but not this one. Were there any concerns?
> 

Sorry I forgot to actually provide an explanation for that - yes, I do have some
comment about this one.

Despite this being a load switch, it's still switching power from regulator A to
target device X, so this is technically still providing 3.3V to device X.

Think about how a "regular" full-fledged regulator works: you can (sometimes) set
a voltage, and then you can ENABLE the VOUT for said regulator (/rail): this kind
of "load switch" does exactly the same as the ENABLE switch for a full-fledged
regulator.

So, this is switching on and off a power rail that is derived from a source rail,
practically creating... well, a "new" rail, with...

  VIN=somewhere-3.3v,
  VOUT=somewhere-still-3.3v

Any objections/doubts/etc? :-)

P.S.: I'm writing fast, sorry if anything appears unclear, feel free to shoot more
       questions in case :-)

Cheers,
Angelo

> 
> ChenYu
> 
>> ---
>>   arch/arm64/boot/dts/mediatek/mt8183-kukui-jacuzzi.dtsi | 2 --
>>   1 file changed, 2 deletions(-)
>>
>> diff --git a/arch/arm64/boot/dts/mediatek/mt8183-kukui-jacuzzi.dtsi b/arch/arm64/boot/dts/mediatek/mt8183-kukui-jacuzzi.dtsi
>> index 783c333107bc..7bbafe926558 100644
>> --- a/arch/arm64/boot/dts/mediatek/mt8183-kukui-jacuzzi.dtsi
>> +++ b/arch/arm64/boot/dts/mediatek/mt8183-kukui-jacuzzi.dtsi
>> @@ -35,8 +35,6 @@ pp1800_mipibrdg: pp1800-mipibrdg {
>>          pp3300_panel: pp3300-panel {
>>                  compatible = "regulator-fixed";
>>                  regulator-name = "pp3300_panel";
>> -               regulator-min-microvolt = <3300000>;
>> -               regulator-max-microvolt = <3300000>;
>>                  pinctrl-names = "default";
>>                  pinctrl-0 = <&pp3300_panel_pins>;
>>
>> --
>> 2.47.0.163.g1226f6d8fa-goog
>>