Re: [PATCH 13/14] arm64: dts: renesas: rzg3s-smarc-som: Enable Ethernet interfaces

From: claudiu beznea <claudiu.beznea@tuxon.dev>
To: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: s.shtylyov@omp.ru, davem@davemloft.net, edumazet@google.com,
	kuba@kernel.org, pabeni@redhat.com, robh+dt@kernel.org,
	krzysztof.kozlowski+dt@linaro.org, conor+dt@kernel.org,
	linux@armlinux.org.uk, magnus.damm@gmail.com,
	mturquette@baylibre.com, sboyd@kernel.org,
	linus.walleij@linaro.org, p.zabel@pengutronix.de, arnd@arndb.de,
	m.szyprowski@samsung.com, alexandre.torgue@foss.st.com,
	afd@ti.com, broonie@kernel.org, alexander.stein@ew.tq-group.com,
	eugen.hristev@collabora.com, sergei.shtylyov@gmail.com,
	prabhakar.mahadev-lad.rj@bp.renesas.com,
	biju.das.jz@bp.renesas.com, linux-renesas-soc@vger.kernel.org,
	netdev@vger.kernel.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, linux-clk@vger.kernel.org,
	linux-gpio@vger.kernel.org,
	Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Subject: Re: [PATCH 13/14] arm64: dts: renesas: rzg3s-smarc-som: Enable Ethernet interfaces
Date: Wed, 6 Dec 2023 13:48:26 +0200	[thread overview]
Message-ID: <89b68781-b552-499d-a8f2-df4dccbb02e0@tuxon.dev> (raw)
In-Reply-To: <CAMuHMdXs9tKo9W31f5OybNR51a_i99Lyx=wHe0GLrADN_8KZTg@mail.gmail.com>

Hi, Geert,

On 06.12.2023 13:22, Geert Uytterhoeven wrote:
> Hi Claudiu,
> 
> Thanks for your patch!
> 
> On Mon, Nov 20, 2023 at 8:03 AM Claudiu <claudiu.beznea@tuxon.dev> wrote:
>> From: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
>>
>> RZ/G3S Smarc Module has Ethernet PHYs (KSZ9131) connected to each Ethernet
>> IP. For this add proper DT bindings to enable the Ethernet communication
>> though these PHYs.
>>
>> The interface b/w PHYs and MACs is RGMII. The skew settings were set to
>> zero as based on phy-mode (rgmii-id) the KSZ9131 driver enables internal
>> DLL which adds 2ns delay b/w clocks (TX/RX) and data signals.
> 
> So shouldn't you just use phy-mode "rgmii" instead?

I chose it like this for simpler configuration of the skew settings. The
PHY supports fixed 2ns delays which is enough for RGMII. And this is
configured based on phy-mode="rgmii-id". As this delay depends also on
soldering length I consider it better this way.

The other variant would have been using phy-mode="rgmii" + skew settings.

Also, same phy-mode is used by rzg2ul-smarc-som.dtsi which is using the
same PHY.

>> Different pin settings were applied to TXC, TX_CTL compared with the rest
>> of the RGMII pins to comply with requirements for these pins imposed by
>> HW manual of RZ/G3S (see chapters "Ether Ch0 Voltage Mode Control
>> Register (ETH0_POC)", "Ether Ch1 Voltage Mode Control Register (ETH1_POC)",
>> for power source selection, "Ether MII/RGMII Mode Control Register
>> (ETH_MODE)" for output-enable and "Input Enable Control Register (IEN_m)"
>> for input-enable configurations).
>>
>> Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
> 
>> --- a/arch/arm64/boot/dts/renesas/rzg3s-smarc-som.dtsi
>> +++ b/arch/arm64/boot/dts/renesas/rzg3s-smarc-som.dtsi
>> @@ -25,7 +25,10 @@ / {
>>
>>         aliases {
>>                 mmc0 = &sdhi0;
>> -#if !SW_SD2_EN
>> +#if SW_SD2_EN
> 
> Cfr. my comment on [PATCH 11/14], this looks odd...
> 
>> +               eth0 = &eth0;
>> +               eth1 = &eth1;
>> +#else
>>                 mmc2 = &sdhi2;
>>  #endif
>>         };
>> @@ -81,6 +84,64 @@ vcc_sdhi2: regulator2 {
>>         };
>>  };
>>
>> +#if SW_SD2_EN
> 
> Likewise.
> 
>> +&eth0 {
>> +       pinctrl-0 = <&eth0_pins>;
>> +       pinctrl-names = "default";
>> +       phy-handle = <&phy0>;
>> +       phy-mode = "rgmii-id";
>> +       #address-cells = <1>;
>> +       #size-cells = <0>;
> 
> #{address,size}-cells should be in the SoC-specific .dtsi.
> Same for eth1.
> 
>> +       status = "okay";
> 
> The rest LGTM.
> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds
> 
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