linux-kernel - Re: [PATCH v3 1/2] dt-bindings: PCI: mediatek-gen3: Add property to disable dvfsrc voltage request

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Message-ID: <20210716173333.GA3632722@robh.at.kernel.org>
Date:   Fri, 16 Jul 2021 11:33:33 -0600
From:   Rob Herring <robh@...nel.org>
To:     Jianjun Wang <jianjun.wang@...iatek.com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Ryder Lee <ryder.lee@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        linux-pci@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, youlin.pei@...iatek.com,
        chuanjia.liu@...iatek.com, qizhong.cheng@...iatek.com,
        ot_jieyang@...iatek.com, drinkcat@...omium.org,
        Rex-BC.Chen@...iatek.com, Krzysztof Wilczyski <kw@...ux.com>,
        Ryan-JH.Yu@...iatek.com
Subject: Re: [PATCH v3 1/2] dt-bindings: PCI: mediatek-gen3: Add property to
 disable dvfsrc voltage request

On Wed, Jun 30, 2021 at 10:49:33AM +0800, Jianjun Wang wrote:
> Add property to disable dvfsrc voltage request, if this property
> is presented, we assume that the requested voltage is always
> higher enough to keep the PCIe controller active.
> 
> Signed-off-by: Jianjun Wang <jianjun.wang@...iatek.com>
> ---
>  .../devicetree/bindings/pci/mediatek-pcie-gen3.yaml       | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/pci/mediatek-pcie-gen3.yaml b/Documentation/devicetree/bindings/pci/mediatek-pcie-gen3.yaml
> index e7b1f9892da4..3e26c032cea9 100644
> --- a/Documentation/devicetree/bindings/pci/mediatek-pcie-gen3.yaml
> +++ b/Documentation/devicetree/bindings/pci/mediatek-pcie-gen3.yaml
> @@ -96,6 +96,12 @@ properties:
>    phys:
>      maxItems: 1
>  
> +  disable-dvfsrc-vlt-req:
> +    description: Disable dvfsrc voltage request, if this property is presented,
> +      we assume that the requested voltage is always higher enough to keep
> +      the PCIe controller active.
> +    type: boolean

What determines setting this property? Can it be implied by the 
compatible (which should be SoC specific).

Is this property specific to PCIe controller? 

Wouldn't the request be harmless to make the voltage request even if not 
needed?

I think this probably should be addressed in a common way as part of 
other QoS, devfreq, etc. requirements for devices.

Rob