linux-kernel - Re: [PATCH 2/3] arm64: dts: qcom: sa8295p: Enable tertiary controller and its 4 USB ports

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Date: Thu, 8 Feb 2024 10:18:12 +0530
From: Krishna Kurapati PSSNV <quic_kriskura@...cinc.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
CC: Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Konrad Dybcio
	<konrad.dybcio@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Bjorn Andersson
	<andersson@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-msm@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <quic_ppratap@...cinc.com>, <quic_jackp@...cinc.com>
Subject: Re: [PATCH 2/3] arm64: dts: qcom: sa8295p: Enable tertiary controller
 and its 4 USB ports



On 2/8/2024 10:11 AM, Dmitry Baryshkov wrote:
> On Thu, 8 Feb 2024 at 04:40, Krishna Kurapati PSSNV
> <quic_kriskura@...cinc.com> wrote:
>> On 2/6/2024 6:54 PM, Dmitry Baryshkov wrote:
>>> On Tue, 6 Feb 2024 at 14:28, Krishna Kurapati PSSNV
>>> <quic_kriskura@...cinc.com> wrote:
>>>>
>>>>
>>>>
>>>> On 2/6/2024 5:43 PM, Dmitry Baryshkov wrote:
>>>>> On Tue, 6 Feb 2024 at 14:03, Krishna Kurapati <quic_kriskura@...cinc.com> wrote:
>>>>>>
>>>>>> Enable tertiary controller for SA8295P (based on SC8280XP).
>>>>>> Add pinctrl support for usb ports to provide VBUS to connected peripherals.
>>>>>
>>>>> These are not just pinctrl entries. They hide VBUS regulators. Please
>>>>> implement them properly as corresponding vbus regulators.
>>>>>
>>>>
>>>> Hi Dmitry. Apologies, can you elaborate on your comment. I thought this
>>>> implementation was fine as Konrad reviewed it in v13 [1]. I removed his
>>>> RB tag as I made one change of dropping "_state" in labels.
>>>
>>> My comment is pretty simple: if I'm not mistaken, your DT doesn't
>>> reflect your hardware design.
>>> You have actual VBUS regulators driven by these GPIO pins. Is this correct?
>>> If so, you should describe them properly in the device tree rather
>>> than describing them just as USB host's pinctrl state.
>>>
>>
>> Hi Dmitry,
>>
>>    I have very little idea about the gpio controller regulators. I will
>> go through it and see how I can implement it. I just found this :
>> https://www.kernel.org/doc/Documentation/devicetree/bindings/regulator/gpio-regulator.txt
> 
> Much simpler, it can be found at
> Documentation/devicetree/bindings/regulator/fixed-regulator.yaml

Thanks for the reference.

> 
>> One query. If we model it as a regulator, do we need to add it as a
>> supply and call regulator_enable in dwc3_qcom probe again ?
> 
> Not in probe(), but yes. It needs to be enabled when the VBUS has to
> be powered up, when the device is initialised or switched to the host
> mode, and disabled when the VBUS has to be powered down, if the device
> is being switched to the device mode.
> 

Actually since we never go to device mode, can't we just stick to this 
pinctrl approach and skip turning on regulator in driver ?

Regards,
Krishna,