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

[Drew Fustini]

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@xxxxxxxxxxxx>
> > ---
> >  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