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From:   Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Date:   Fri, 1 May 2020 16:49:02 +0200
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Subject: Re: [PATCH RFC v2 00/11] dwmac-meson8b Ethernet RX delay configuration
To:     Andrew Lunn <andrew@lunn.ch>
Cc:     robh+dt@kernel.org, f.fainelli@gmail.com,
        linux-amlogic@lists.infradead.org, devicetree@vger.kernel.org,
        jianxin.pan@amlogic.com, davem@davemloft.net,
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Hi Andrew,

On Wed, Apr 29, 2020 at 11:29 PM Andrew Lunn <andrew@lunn.ch> wrote:
>
> > - 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
>
> Hi Martin
>
> Can you actually see this on the PCB? The other possibility is that
> the bootloader is configuring something, which is not getting
> overridden when linux starts up.
at least it doesn't jump straight into my eye.
I checked in u-boot and Linux, and for both the RX delay is disabled
in the PHY as well as in the MAC.

The schematics of the Khadas VIM2 also show the the RX delay in the
PHY is turned off by pin-strapping, see page 7 on the right: [0]
It's the same for the Khadas VIM3 schematics, also on page 7: [1]
There are also high resolution images of the Khadas VIM3 online so you
can look at it yourself (I couldn't find any for the Khadas VIM2 which
is what I have): [2]

I agree that we need to get an answer to the RX delay question on the
arm64 SoCs.
If there's no way to find out from the existing resources then I can
contact Khadas and ask them about the PCB trace length on VIM2, VIM3
and VIM3L (these are the ones with RGMII PHYs).

For the older SoCs the RX delay has to be provided by either the MAC
or the PHY and right now we're not configuring it.
We cannot simply enable the RX delay at the PHY level because the
bootloader enables it in the MAC (so we have to turn it off there).
So it would be great if you could still review this series.


Martin


[0] https://dl.khadas.com/Hardware/VIM2/Schematic/VIM2_V12_Sch.pdf
[1] https://dl.khadas.com/Hardware/VIM3/Schematic/VIM3_V12_Sch.pdf
[2] https://forum.khadas.com/t/khadas-vim3-is-launching-on-24-june/4103