linux-kernel - Re: [PATCH 1/3] dt-bindings: phy: qcom,qmp-pcie: add optional current load properties

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Message-ID: <3c7ddb08-38db-44b3-a7a7-ec7b270a408f@kernel.org>
Date: Wed, 11 Dec 2024 10:52:11 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc: Ziyue Zhang <quic_ziyuzhan@...cinc.com>, vkoul@...nel.org,
 kishon@...nel.org, dmitry.baryshkov@...aro.org, abel.vesa@...aro.org,
 neil.armstrong@...aro.org, andersson@...nel.org, konradybcio@...nel.org,
 robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org,
 linux-arm-msm@...r.kernel.org, linux-phy@...ts.infradead.org,
 linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH 1/3] dt-bindings: phy: qcom,qmp-pcie: add optional current
 load properties

On 11/12/2024 09:24, Manivannan Sadhasivam wrote:
> On Wed, Dec 11, 2024 at 09:09:18AM +0100, Krzysztof Kozlowski wrote:
>> On 11/12/2024 07:20, Manivannan Sadhasivam wrote:
>>> On Thu, Dec 05, 2024 at 11:23:11AM +0100, Krzysztof Kozlowski wrote:
>>>> On Wed, Dec 04, 2024 at 06:52:47PM +0800, Ziyue Zhang wrote:
>>>>> On some platforms, the power supply for PCIe PHY is not able to provide
>>>>> enough current when it works in LPM mode. Hence, PCIe PHY driver needs to
>>>>> set current load to vote the regulator to HPM mode.
>>>>>
>>>>> Document the current load as properties for each power supply PCIe PHY
>>>>> required, namely vdda-phy-max-microamp, vdda-pll-max-microamp and
>>>>> vdda-qref-max-microamp, respectively.PCIe PHY driver should parse them to
>>>>> set appropriate current load during PHY power on.
>>>>>
>>>>> This three properties are optional and not mandatory for those platforms
>>>>> that PCIe PHY can still work with power supply.
>>>>
>>>>
>>>> Uh uh, so the downstream comes finally!
>>>>
>>>> No sorry guys, use existing regulator bindings for this.
>>>>
>>>
>>> Maybe they got inspired by upstream UFS bindings?
>>> Documentation/devicetree/bindings/ufs/ufs-common.yaml:
>>>
>>> vcc-max-microamp
>>> vccq-max-microamp
>>> vccq2-max-microamp
>>
>> And it is already an ABI, so we cannot do anything about it.
>>
>>>
>>> Regulator binding only describes the min/max load for the regulators and not
>>
>> No, it exactly describes min/max consumers can use. Let's quote:
>> "largest current consumers may set"
>> It is all about consumers.
>>
>>> consumers. What if the consumers need to set variable load per platform? Should
>>
>> Then each platform uses regulator API or regulator bindings to set it? I
>> don't see the problem here.
>>
>>> they hardcode the load in driver? (even so, the load should not vary for each
>>> board).
>>
>> The load must vary per board, because regulators vary per board. Of
>> course in practice most designs could be the same, but regulators and
>> their limits are always properties of the board, not the SoC.
>>
> 
> How the consumer drivers are supposed to know the optimum load?
> 
> I don't see how the consumer drivers can set the load without hardcoding the
> values. And I could see from UFS properties that each board has different
> values.


Drivers do not need to know, it's not the driver's responsibility. If
these are constraints per board, then regulator properties apply and
there is no difference between this "vdd-max-microamp = 10" and
"regulator-max-microamp".

If this varies runtime, then your property is already not suitable and
very limited and you should use OPP table.

Best regards,
Krzysztof