[PATCH RFC v2 00/11] dwmac-meson8b Ethernet RX delay configuration

[Martin Blumenstingl <martin.blumenstingl@googlemail.com>]

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 last 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


Changes since RFC v1 at [1]:
- add support for the timing adjustment clock input (dt-bindings and
  in the driver) thanks to the input from the unnamed Ethernet engineer
  at Amlogic. This is the missing link between the fclk_div2 clock and
  the Ethernet controller on Meson8b (no traffic would flow if that
  clock was disabled)
- add support fot the amlogic,rx-delay-ns property. The only supported
  values so far are 0ns and 2ns. The registers seem to allow more
  precise timing adjustments, but I could not make that work so far.
- add more register documentation (for the new RX delay bits) and
  unified the placement of existing register documentation. Again,
  thanks to Jianxin and the unnamed Ethernet engineer at Amlogic
- DO NOT MERGE: .dts patches to show the conversion of the Meson8b
  and Meson8m2 boards to "rgmii-id". I didn't have time for all arm64
  patches yet, but these will switch to phy-mode = "rgmii-txid" with
  amlogic,rx-delay-ns = <0> (because the delay seems to be provided by
  the PCB trace length).


[0] https://patchwork.kernel.org/patch/11309891/
[1] https://patchwork.kernel.org/cover/11310719/


Martin Blumenstingl (11):
  dt-bindings: net: meson-dwmac: Add the amlogic,rx-delay-ns property
  dt-bindings: net: dwmac-meson: Document the "timing-adjustment" clock
  net: stmmac: dwmac-meson8b: use FIELD_PREP instead of open-coding it
  net: stmmac: dwmac-meson8b: Move the documentation for the TX delay
  net: stmmac: dwmac-meson8b: Add the PRG_ETH0_ADJ_* bits
  net: stmmac: dwmac-meson8b: Fetch the "timing-adjustment" clock
  net: stmmac: dwmac-meson8b: Make the clock enabling code re-usable
  net: stmmac: dwmac-meson8b: add support for the RX delay configuration
  arm64: dts: amlogic: Add the Ethernet "timing-adjustment" clock
  ARM: dts: meson: Add the Ethernet "timing-adjustment" clock
  ARM: dts: meson: Switch existing boards with RGMII PHY to "rgmii-id"

 .../bindings/net/amlogic,meson-dwmac.yaml     |  23 ++-
 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 +-
 arch/arm64/boot/dts/amlogic/meson-axg.dtsi    |   6 +-
 .../boot/dts/amlogic/meson-g12-common.dtsi    |   6 +-
 arch/arm64/boot/dts/amlogic/meson-gxbb.dtsi   |   5 +-
 arch/arm64/boot/dts/amlogic/meson-gxl.dtsi    |   5 +-
 .../ethernet/stmicro/stmmac/dwmac-meson8b.c   | 140 ++++++++++++++----
 10 files changed, 150 insertions(+), 52 deletions(-)

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2.26.2