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Date:   Tue, 12 May 2020 23:10:55 +0200
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     robh+dt@...nel.org, andrew@...n.ch, f.fainelli@...il.com,
        linux-amlogic@...ts.infradead.org, devicetree@...r.kernel.org
Cc:     jianxin.pan@...ogic.com, davem@...emloft.net,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Subject: [PATCH v3 0/8] dwmac-meson8b Ethernet RX delay configuration

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.


Dependencies for this series:
There is a soft dependency for patch #2 on commit f22531438ff42c
"dt-bindings: net: dwmac: increase 'maxItems' for 'clocks',
'clock-names' properties" which is currently in Rob's -next tree.
That commit is needed to make the dt-bindings schema validation
pass for patch #2. That patch has been for ~4 weeks in Robs tree,
so I assume that is not going to be dropped.


Changes since RFC v2 at [2]:
- dropped $ref: /schemas/types.yaml#definitions/uint32 from the
  "amlogic,rx-delay-ns" in patch #1 ("Don't need to define the
  type when in standard units." says Rob - thanks, I learned
  something new). Also use "default: 0" for for this property
  instead of explaining it in the description text.
- added a note to the cover-letter about a hidden dependency for
  dt-binding schema validation in patch #2
- Added Andrew's Reviewed-by to patches 1-7. Thank you again for
  the quick and detailed reviews, I appreciate this!
- error out if the (optional) timing-adjustment clock is missing
  but we're asked to enable the RGMII RX delay. The MAC won't
  work in this specific case and either the RX delay has to be
  provided by the PHY or the timing-adjustment clock has to be
  added.
- dropped the dts patches (#9-11) which were only added to give
  an overview how this is going to be used. those will be sent
  separately
- dropped the RFC prefix

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/
[2] https://patchwork.kernel.org/cover/11518257/


Martin Blumenstingl (8):
  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

 .../bindings/net/amlogic,meson-dwmac.yaml     |  23 ++-
 .../ethernet/stmicro/stmmac/dwmac-meson8b.c   | 146 ++++++++++++++----
 2 files changed, 134 insertions(+), 35 deletions(-)

-- 
2.26.2

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