linux-kernel - Re: [PATCH v2 4/4] arm64: dts: qcom: x1e80100-qcp: Add qref supply for PCIe PHYs

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Message-ID: <17a1a4d9-fdc5-477a-bf4e-91cae5a62479@oss.qualcomm.com>
Date: Sat, 26 Apr 2025 12:48:38 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Johan Hovold <johan@...nel.org>,
        Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Cc: Wenbin Yao <quic_wenbyao@...cinc.com>, catalin.marinas@....com,
        will@...nel.org, linux-arm-kernel@...ts.infradead.org,
        andersson@...nel.org, konradybcio@...nel.org, robh@...nel.org,
        krzk+dt@...nel.org, conor+dt@...nel.org, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        krishna.chundru@....qualcomm.com, quic_vbadigan@...cinc.com,
        quic_mrana@...cinc.com, quic_cang@...cinc.com, quic_qianyu@...cinc.com
Subject: Re: [PATCH v2 4/4] arm64: dts: qcom: x1e80100-qcp: Add qref supply
 for PCIe PHYs

On 4/25/25 2:02 PM, Johan Hovold wrote:
> On Fri, Apr 25, 2025 at 12:03:06PM +0200, Konrad Dybcio wrote:
>> On 4/25/25 11:51 AM, Johan Hovold wrote:
>>> On Fri, Apr 25, 2025 at 05:29:55PM +0800, Wenbin Yao wrote:
>>>> From: Qiang Yu <quic_qianyu@...cinc.com>
>>>>
>>>> All PCIe PHYs on X1E80100 require vdda-qref power supplies, but this is
>>>> missing in the current PHY device tree node. The PCIe port can still
>>>> function because the regulator L3J, which vdda-qref consumes, is voted by
>>>> other components.
>>>>
>>>> Since the device tree should accurately describe the hardware, add the
>>>> vdda-qref power supply explicitly in all PCIe PHY device nodes.
>>>
>>> AFAIU the PHYs do not use this qref supply directly so it does not
>>> belong in the PHY node (but possibly in the tcsr node that provides the
>>> refclk).
>>>
>>> Since commit 031b46b4729b ("phy: qcom: qmp-pcie: drop bogus x1e80100
>>> qref supplies") it also won't have any effect for pcie4 and pcie6.
>>
>> QREF is a separate hw block distributing the reference clocks across
>> certain on-SoC peripherals
>>
>> If its power goes out, I don't think much of the platform would be
>> functional anyway, so it's redundant here..
>>
>> It doesn't have its own single register region and it's frankly
>> one-shot-configured way before Linux starts up, so there should be
>> no need of describing it at all.
> 
> Then it sounds like the qref supplies should be marked as always-on. Can
> they be disabled at all?

The best answer I can say is "maybe". I would (without knowing any better)
assume RPMh wouldn't let you turn them off. QREF predictably takes VDD_CX/MX
and some additional lines

Konrad