netdev - Re: [PATCH v3 0/8] dwmac-meson8b Ethernet RX delay configuration

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Message-Id: <20200513.122338.1849377923675371554.davem@davemloft.net>
Date:   Wed, 13 May 2020 12:23:38 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     martin.blumenstingl@...glemail.com
Cc:     robh+dt@...nel.org, andrew@...n.ch, f.fainelli@...il.com,
        linux-amlogic@...ts.infradead.org, devicetree@...r.kernel.org,
        jianxin.pan@...ogic.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 0/8] dwmac-meson8b Ethernet RX delay configuration

From: Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Date: Tue, 12 May 2020 23:10:55 +0200

> The Ethernet TX performance has been historically bad on Meson8b and
> Meson8m2 SoCs because high packet loss was seen. I found out that this
> was related (yet again) to the RGMII TX delay configuration.
> In the process of discussing the big picture (and not just a single
> patch) [0] with Andrew I discovered that the IP block behind the
> dwmac-meson8b driver actually seems to support the configuration of the
> RGMII RX delay (at least on the Meson8b SoC generation).
> 
> Since I sent the first RFC I got additional documentation from Jianxin
> (many thanks!). Also I have discovered some more interesting details:
> - Meson8b Odroid-C1 requires an RX delay (by either the PHY or the MAC)
>   Based on the vendor u-boot code (not upstream) I assume that it will
>   be the same for all Meson8b and Meson8m2 boards
> - Khadas VIM2 seems to have the RX delay built into the PCB trace
>   length. When I enable the RX delay on the PHY or MAC I can't get any
>   data through. I expect that we will have the same situation on all
>   GXBB, GXM, AXG, G12A, G12B and SM1 boards. Further clarification is
>   needed here though (since I can't visually see these lengthened
>   traces on the PCB). This will be done before sending patches for
>   these boards.
 ...

Series applied to net-next, thanks Martin.