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

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Message-ID: <ZRCkTqV2qV/tMb4O@x1>
Date:   Sun, 24 Sep 2023 23:04:14 +0200
From:   Drew Fustini <dfustini@...libre.com>
To:     Guo Ren <guoren@...nel.org>
Cc:     Conor Dooley <conor@...nel.org>,
        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>,
        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 Sat, Sep 23, 2023 at 04:10:11PM +0800, Guo Ren wrote:
> On Fri, Sep 22, 2023 at 11:18 PM Drew Fustini <dfustini@...libre.com> wrote:
> >
> > 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.
> It's for the PHY debug. You could directly remove them, or keep it
> with no-pull-up flag, then no pull-up flag in the dts for default..

Thank you for explaining that the purpose of the pull-up DT property
was for PHY debug.

I will plan to remove the pull-up DT property in the next version of
this patch series and remove sdhci_phy_1_8v_init_no_pull() and
sdhci_phy_3_3v_init_no_pull() from my sdhci-of-dwcmshc.c patch.

I will make th1520_phy_1_8v_init() and th1520_phy_3_3v_init() always
set WEAKPULL_EN = 1 (PULLUP) for CMDPAD_CNFG, DATAPAD_CNFG, RSTNPAD_CNFG
and set WEAKPULL_EN = 2 (PULLDOWN) for STBPAD_CNFG.

Thanks,
Drew