netdev - Re: [PATCH v4 13/18] arm64: allwinner: sun50i-a64: add dwmac-sun8i Ethernet driver

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Date:   Mon, 24 Apr 2017 20:58:44 +0800
From:   Chen-Yu Tsai <wens@...e.org>
To:     Corentin Labbe <clabbe.montjoie@...il.com>
Cc:     Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Chen-Yu Tsai <wens@...e.org>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        alexandre.torgue@...com,
        linux-sunxi <linux-sunxi@...glegroups.com>,
        devicetree <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v4 13/18] arm64: allwinner: sun50i-a64: add dwmac-sun8i
 Ethernet driver

On Mon, Apr 24, 2017 at 8:24 PM, Corentin Labbe
<clabbe.montjoie@...il.com> wrote:
> On Wed, Apr 12, 2017 at 02:41:53PM +0200, Maxime Ripard wrote:
>> On Wed, Apr 12, 2017 at 01:13:55PM +0200, Corentin Labbe wrote:
>> > The dwmac-sun8i is an Ethernet MAC that supports 10/100/1000 Mbit
>> > connections. It is very similar to the device found in the Allwinner
>> > H3, but lacks the internal 100 Mbit PHY and its associated control
>> > bits.
>> > This adds the necessary bits to the Allwinner A64 SoC .dtsi, but keeps
>> > it disabled at this level.
>> >
>> > Signed-off-by: Corentin Labbe <clabbe.montjoie@...il.com>
>> > ---
>> >  arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi | 37 +++++++++++++++++++++++++++
>> >  1 file changed, 37 insertions(+)
>> >
>> > diff --git a/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi b/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi
>> > index 0b0f4ab..2569827 100644
>> > --- a/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi
>> > +++ b/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi
>> > @@ -287,6 +287,23 @@
>> >                             bias-pull-up;
>> >                     };
>> >
>> > +                   rmii_pins: rmii_pins {
>> > +                           pins = "PD10", "PD11", "PD13", "PD14",
>> > +                                           "PD17", "PD18", "PD19", "PD20",
>> > +                                           "PD22", "PD23";
>>
>> Please align the wrapped lines on the first pin.
>>
>
> OK
>
>> > +                           function = "emac";
>> > +                           drive-strength = <40>;
>>
>> Do you actually need that for all the boards, or only a few of them?
>
> I have tried to use lower value without success on some boards. (opipc/pine64 in my memory)

FYI we need them for all the boards that use RGMII.
The signals at gigabit speed run at 125 MHz DDR.

For RMII we probably don't need it. Even at 100 Mbps,
it's only 50 MHz SDR. drive-strength = <30> should be
enough.

ChenYu