linux-kernel - Re: [RFC v1 0/2] dwmac-meson8b Ethernet RX delay configuration

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Date:   Tue, 7 Jan 2020 15:01:13 +0100
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     jianxin.pan@...ogic.com
Cc:     davem@...emloft.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        andrew@...n.ch, f.fainelli@...il.com,
        linux-amlogic@...ts.infradead.org
Subject: Re: [RFC v1 0/2] dwmac-meson8b Ethernet RX delay configuration

Hello Jianxin,

On Thu, Dec 26, 2019 at 9:37 PM Martin Blumenstingl
<martin.blumenstingl@...glemail.com> wrote:
>
> 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).
>
> The goal of this series is to start the discussion around how to
> implement the RGMII RX delay on this IP block. Additionally it seems
> that the RX delay can also be applied for RMII PHYs?
>
> @Jianxin: can you please add the Amlogic internal Ethernet team to this
> discussion? My questions are documented in the patch description of
> patch #2.
do you already have an update for me on this topic?

while we're discussing unknown bits of the Ethernet controller I also
remembered that we're currently not describing the relation between
the "fclk_div2" clock and the Ethernet controller. however, as
described in commit 72e1f230204039 ("clk: meson: meson8b: mark
fclk_div2 gate clocks as CLK_IS_CRITICAL") this is needed for RGMII
mode.
it would be great to know the relation between fclk_div2 and RGMII
mode on the Ethernet controller!


Thank you!
Martin