netdev - Re: [PATCH 2/2] net: ethernet: stmicro: stmmac: dwmac-rk: Add rv1126 support

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Date:   Thu, 1 Sep 2022 12:56:09 +0530
From:   Jagan Teki <jagan@...eble.ai>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Anand Moon <anand@...eble.ai>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...opsys.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Sugar Zhang <sugar.zhang@...k-chips.com>,
        David Wu <david.wu@...k-chips.com>, netdev@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] net: ethernet: stmicro: stmmac: dwmac-rk: Add rv1126 support

On Mon, 29 Aug 2022 at 18:40, Andrew Lunn <andrew@...n.ch> wrote:
>
> On Mon, Aug 29, 2022 at 06:50:42AM +0000, Anand Moon wrote:
> > Rockchip RV1126 has GMAC 10/100/1000M ethernet controller
> > via RGMII and RMII interfaces are configured via M0 and M1 pinmux.
> >
> > This patch adds rv1126 support by adding delay lines of M0 and M1
> > simultaneously.
>
> What does 'delay lines' mean with respect to RGMII?

These are MAC receive clock delay lengths.

>
> The RGMII signals need a 2ns delay between the clock and the data
> lines. There are three places this can happen:
>
> 1) In the PHY
> 2) Extra long lines on the PCB
> 3) In the MAC
>
> Generally, 1) is used, and controlled via phy-mode. A value of
> PHY_INTERFACE_MODE_RGMII_ID passed to the PHY driver means it will add
> these delays.
>
> You don't want both the MAC and the PHY adding delays.

Yes, but these are specific to MAC, not related to PHY delays. Similar
to what is there in other Rockchip SoC families like RK3366, 3368,
3399, 3128, but these MAC clock delay lengths are grouped based on the
iomux group in RV1126. We have iomux group 0 (M0) and group 1 (M1), so
the rgmii has to set these lengths irrespective of whether PHY add's
or not.

Thanks,
Jagan.