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: <dbae65c4e56a7d445905245be9e3f3d3f3b68d89.camel@mediatek.com>
Date:   Thu, 19 Aug 2021 03:40:43 +0000
From:   Jianjun Wang (王建军) 
        <Jianjun.Wang@...iatek.com>
To:     "robh@...nel.org" <robh@...nel.org>
CC:     "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Youlin Pei (裴友林) 
        <youlin.pei@...iatek.com>,
        "ot_jieyang@...iatek.com" <ot_jieyang@...iatek.com>,
        "drinkcat@...omium.org" <drinkcat@...omium.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        Chuanjia Liu (柳传嘉) 
        <Chuanjia.Liu@...iatek.com>,
        Ryan-JH Yu (余家豪) 
        <Ryan-JH.Yu@...iatek.com>,
        Qizhong Cheng (程啟忠) 
        <Qizhong.Cheng@...iatek.com>, "kw@...ux.com" <kw@...ux.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        Ryder Lee (李庚諺) <Ryder.Lee@...iatek.com>,
        Rex-BC Chen (陳柏辰) 
        <Rex-BC.Chen@...iatek.com>
Subject: Re: [PATCH v3 1/2] dt-bindings: PCI: mediatek-gen3: Add property to
 disable dvfsrc voltage request

On Fri, 2021-07-16 at 11:33 -0600, Rob Herring wrote:
> 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

Hi Rob,

Thanks for your review and sorry for the late response.

We have internal discussion and we agree with that this feature should
not be specific to the PCIe controller, we need to find a common way to
do this. 

But as the driver of dvfsrc is not finished the upstream, we don't have
a better solution for now, so we would like to pull back this patch and
will send another patch to disable dvfsrc by default until we find a
common solution to enable it.

Thanks.