linux-kernel - Re: [PATCH v2 3/5] arm64: dts: allwinner: a523: Add EMAC0 ethernet MAC

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Message-ID: <CAGb2v65QUrCjgHXWAb72Sdppqg1AUxXyD_ZcXShtkRSHCQBbOg@mail.gmail.com>
Date: Fri, 25 Apr 2025 22:35:59 +0800
From: Chen-Yu Tsai <wens@...e.org>
To: Andre Przywara <andre.przywara@....com>
Cc: Yixun Lan <dlan@...too.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Jernej Skrabec <jernej.skrabec@...il.com>, Samuel Holland <samuel@...lland.org>, 
	Maxime Ripard <mripard@...nel.org>, Andrew Lunn <andrew+netdev@...n.ch>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Corentin Labbe <clabbe.montjoie@...il.com>, devicetree@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH v2 3/5] arm64: dts: allwinner: a523: Add EMAC0 ethernet MAC

On Fri, Apr 25, 2025 at 5:41 PM Andre Przywara <andre.przywara@....com> wrote:
>
> On Fri, 25 Apr 2025 13:26:25 +0800
> Chen-Yu Tsai <wens@...e.org> wrote:
>
> Hi Chen-Yu,
>
> > On Thu, Apr 24, 2025 at 6:09 PM Yixun Lan <dlan@...too.org> wrote:
> > >
> > > Add EMAC0 ethernet MAC support which found on A523 variant SoCs,
> > > including the A527/T527 chips. MAC0 is compatible to the A64 chip which
> > > requires an external PHY. This patch only add RGMII pins for now.
> > >
> > > Signed-off-by: Yixun Lan <dlan@...too.org>
> > > ---
> > >  arch/arm64/boot/dts/allwinner/sun55i-a523.dtsi | 40 ++++++++++++++++++++++++++
> > >  1 file changed, 40 insertions(+)
> > >
> > > diff --git a/arch/arm64/boot/dts/allwinner/sun55i-a523.dtsi b/arch/arm64/boot/dts/allwinner/sun55i-a523.dtsi
> > > index ee485899ba0af69f32727a53de20051a2e31be1d..c9a9b9dd479af05ba22fe9d783e32f6d61a74ef7 100644
> > > --- a/arch/arm64/boot/dts/allwinner/sun55i-a523.dtsi
> > > +++ b/arch/arm64/boot/dts/allwinner/sun55i-a523.dtsi
> > > @@ -126,6 +126,15 @@ pio: pinctrl@...0000 {
> > >                         interrupt-controller;
> > >                         #interrupt-cells = <3>;
> > >
> > > +                       rgmii0_pins: rgmii0-pins {
> > > +                               pins = "PH0", "PH1", "PH2", "PH3", "PH4",
> > > +                                      "PH5", "PH6", "PH7", "PH9", "PH10",
> > > +                                      "PH14", "PH15", "PH16", "PH17", "PH18";
> > > +                               allwinner,pinmux = <5>;
> > > +                               function = "emac0";
> > > +                               drive-strength = <40>;
> >
> > We should probably add
> >
> >                                   bias-disable;
> >
> > to explicitly turn off pull-up and pull-down.
>
> Should we? I don't see this anywhere else for sunxi, probably because it is
> the (reset) default (0b00).
> I wonder if we have a hidden assumption about this? As in: if no bias is
> specified, we assume bias-disable? Then we should maybe enforce this is in
> the driver?

There isn't any assumption, as in we were fine with either the reset
default or whatever the bootloader left it in. However in projects at
work I learned that it's better to have explicit settings despite
working defaults.


ChenYu