linux-kernel - [PATCH 0/2] ARM: dts: meson8b/m2: RGMII improvements

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Message-Id: <20200512215148.540322-1-martin.blumenstingl@googlemail.com>
Date:   Tue, 12 May 2020 23:51:46 +0200
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     linux-amlogic@...ts.infradead.org, khilman@...libre.com
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        andrew@...n.ch,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Subject: [PATCH 0/2] ARM: dts: meson8b/m2: RGMII improvements

Hi Kevin,

the fist patch in this series connects FCLK_DIV2 to the PRG_ETH
"additional" registers for the dwmac Ethernet controller.
Now that we know how RGMII and FCLK_DIV2 are connected we can
add this dependency to get rid of CLK_IS_CRITICAL for FCLK_DIV2
at some point.

The second patch fixes the RX and TX delay. The 4ns TX delay which
we have used so far is incorrect and only worked because we were
using an unsupported clock divider in the PRG_ETH registers. That
divider has been fixed with commit bd6f48546b9c ("net: stmmac:
dwmac-meson8b: Fix the RGMII TX delay on Meson8b/8m2 SoCs").
Instead of "just" fixing the TX delay we can even do better and
switch to phy-mode = "rgmii-id" to let the PHY generate the RX
and TX delay. However, previously we didn't know that there was
an RX delay applied by the MAC on these boards. Only the additional
information from Jianxin in the other series [0] made us aware
of this. Without the other series there will be a 4ns RX delay
(2ns from the MAC and additional 2ns from the PHY). Due to this
dependency I did not add a Fixes tag, because backporting these
.dts patches without their runtime dependency will break stable
kernels.

TL;DR:
Ethernet TX throughput on my Odroid-C1 improved from <200Mbit/s
to >700Mbit/s (measured with iperf3)

Dependencies:
This series has a runtime dependency on v7 of the series called
"dwmac-meson8b Ethernet RX delay configuration" [0]

[0] https://patchwork.kernel.org/cover/11543997/

Martin Blumenstingl (2):
  ARM: dts: meson: Add the Ethernet "timing-adjustment" clock
  ARM: dts: meson: Switch existing boards with RGMII PHY to "rgmii-id"

 arch/arm/boot/dts/meson8b-odroidc1.dts    | 3 +--
 arch/arm/boot/dts/meson8b.dtsi            | 5 +++--
 arch/arm/boot/dts/meson8m2-mxiii-plus.dts | 4 +---
 arch/arm/boot/dts/meson8m2.dtsi           | 5 +++--
 4 files changed, 8 insertions(+), 9 deletions(-)

-- 
2.26.2