linux-kernel - Re: [PATCH 1/2] arm64: dts: qcom: x1e80100-romulus: Describe PCIe power supplies

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Message-ID: <b9fbee18-729f-483a-bdaa-51766a07ca46@oss.qualcomm.com>
Date: Wed, 13 Aug 2025 14:09:51 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Stephan Gerhold <stephan.gerhold@...aro.org>,
        Konrad Dybcio <konradybcio@...nel.org>
Cc: Bjorn Andersson <andersson@...nel.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley
 <conor+dt@...nel.org>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] arm64: dts: qcom: x1e80100-romulus: Describe PCIe
 power supplies

On 8/12/25 5:45 PM, Stephan Gerhold wrote:
> On Tue, Aug 12, 2025 at 03:47:23PM +0200, Konrad Dybcio wrote:
>> From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
>>
>> Describe the power plumbing to allow fully suspending the slot and the
>> connected SD controller.
>>
>> Signed-off-by: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
> 
> Are you sure these supplies really exist on the board? E.g. on the
> x1e001de-devkit, Windows toggles all these GPIOs, but there doesn't seem
> to be anything connected to two of them, the 12V supply is simply always
> on.

Unfortunately, I have no schematics for this board..

I did reverse the polarity (and removed enable-active-high from the vreg
node) to no effect.. so it may be that they're actually unnecessary, i.e.
so is this patch

> 
> Even more importantly, for a laptop I would expect they use some part
> that doesn't need a beefy 12V supply. I don't have the datasheet for
> RTS5261, but e.g. in [1] this chip is explicitly advertised with 3.3V
> power.
> 
> I guess it's hard to be sure without schematics and it surely doesn't
> hurt to toggle these GPIOs like on Windows, but perhaps a comment that
> some of these likely don't exist would be good ...
> 
> [1]: https://www.sdcard.org/cms/wp-content/uploads/2023/06/SDA_computex2023_Realtek.pdf
> 
>> ---

[...]

>> +	sde7_main_reg_en: sde7-main-reg-en-state {
>> +		pins = "gpio6";
>> +		function = "normal";
>> +	};
>> +
>> +	sde7_aux_reg_en: sde7-aux-reg-en-state {
>> +		pins = "gpio8";
>> +		function = "normal";
>> +	};
>>  };
> 
> I think you should either do a full configuration (include power-source
> and everything else essential as well) or omit this entirely, because
> like this you will need the proper configuration from the boot firmware
> anyway.

'function' alone is really important on PMIC GPIOs, fwiw

Konrad