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

From: Martin Blumenstingl <martin.blumenstingl@googlemail.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.

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