linux-kernel - Re: [PATCH 1/6] dt-bindings: mmc: sdhci-of-dwcmhsc: Add T-Head TH1520 support

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Message-ID: <ZQ2tP48Z19C5xRug@x1>
Date:   Fri, 22 Sep 2023 08:18:11 -0700
From:   Drew Fustini <dfustini@...libre.com>
To:     Conor Dooley <conor@...nel.org>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Jisheng Zhang <jszhang@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Guo Ren <guoren@...nel.org>, Fu Wei <wefu@...hat.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Robert Nelson <robertcnelson@...gleboard.org>,
        Jason Kridner <jkridner@...gleboard.org>,
        Xi Ruoyao <xry111@...111.site>, Han Gao <gaohan@...as.ac.cn>,
        Icenowy Zheng <uwu@...nowy.me>, linux-mmc@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH 1/6] dt-bindings: mmc: sdhci-of-dwcmhsc: Add T-Head
 TH1520 support

On Fri, Sep 22, 2023 at 10:57:36AM +0100, Conor Dooley wrote:
> Hey Drew,
> 
> On Thu, Sep 21, 2023 at 06:49:48PM -0700, Drew Fustini wrote:
> > Add compatible value for the T-Head TH1520 dwcmshc controller and add
> > thead,phy-pull-up property.
> > 
> > Signed-off-by: Drew Fustini <dfustini@...libre.com>
> > ---
> >  Documentation/devicetree/bindings/mmc/snps,dwcmshc-sdhci.yaml | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/mmc/snps,dwcmshc-sdhci.yaml b/Documentation/devicetree/bindings/mmc/snps,dwcmshc-sdhci.yaml
> > index a43eb837f8da..46b768d46712 100644
> > --- a/Documentation/devicetree/bindings/mmc/snps,dwcmshc-sdhci.yaml
> > +++ b/Documentation/devicetree/bindings/mmc/snps,dwcmshc-sdhci.yaml
> > @@ -19,6 +19,7 @@ properties:
> >        - rockchip,rk3568-dwcmshc
> >        - rockchip,rk3588-dwcmshc
> >        - snps,dwcmshc-sdhci
> > +      - thead,th1520-dwcmshc
> >  
> >    reg:
> >      maxItems: 1
> > @@ -60,6 +61,9 @@ properties:
> >      description: Specify the number of delay for tx sampling.
> >      $ref: /schemas/types.yaml#/definitions/uint8
> >  
> > +  thead,phy-pull-up:
> > +    description: Enable weak pull-up on PHY pads
> > +    type: boolean
> 
> Why is the weak pull-up required? How would the dts author know if they
> need to use this property?

This is a good question, and I don't have a good reason beyond it is
what the vendor SDK was doing.

There are only two boards right now using the TH1520 that I know of.
Both the LPi4a [1] and the Ahead [2] have the pull-up property set on
all the mmc controller nodes their downstream device trees.

Rob suggested on #devicetree that it would be simpler to just enable it
in the driver and disable support when needed. I like this idea as it
will simplify this binding patch and the code in the driver patch.

Thanks,
Drew

[1] https://git.beagleboard.org/beaglev-ahead/BeagleBoard-DeviceTrees/-/blob/v5.10.x-ti-unified/src/riscv/light-beagle-ref.dts
[2] https://github.com/revyos/thead-kernel/blob/lpi4a/arch/riscv/boot/dts/thead/light-lpi4a-ref.dts