netdev - Re: [PATCH v2 1/7] net: dt-bindings: add RGMII TX delay configuration to meson8b-dwmac

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Date:   Wed, 30 Nov 2016 23:33:38 +0100
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     Rob Herring <robh@...nel.org>
Cc:     linux-amlogic@...ts.infradead.org, devicetree@...r.kernel.org,
        netdev@...r.kernel.org, davem@...emloft.net, khilman@...libre.com,
        mark.rutland@....com, linux-arm-kernel@...ts.infradead.org,
        alexandre.torgue@...com, peppe.cavallaro@...com,
        will.deacon@....com, catalin.marinas@....com, carlo@...one.org,
        f.fainelli@...il.com
Subject: Re: [PATCH v2 1/7] net: dt-bindings: add RGMII TX delay configuration
 to meson8b-dwmac

On Wed, Nov 30, 2016 at 10:44 PM, Rob Herring <robh@...nel.org> wrote:
> On Fri, Nov 25, 2016 at 02:01:50PM +0100, Martin Blumenstingl wrote:
>> This allows configuring the RGMII TX clock delay. The RGMII clock is
>> generated by underlying hardware of the the Meson 8b / GXBB DWMAC glue.
>> The configuration depends on the actual hardware (no delay may be
>> needed due to the design of the actual circuit, the PHY might add this
>> delay, etc.).
>>
>> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@...glemail.com>
>> ---
>>  Documentation/devicetree/bindings/net/meson-dwmac.txt | 14 ++++++++++++++
>>  1 file changed, 14 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/net/meson-dwmac.txt b/Documentation/devicetree/bindings/net/meson-dwmac.txt
>> index 89e62dd..f8bc540 100644
>> --- a/Documentation/devicetree/bindings/net/meson-dwmac.txt
>> +++ b/Documentation/devicetree/bindings/net/meson-dwmac.txt
>> @@ -25,6 +25,20 @@ Required properties on Meson8b and newer:
>>               - "clkin0" - first parent clock of the internal mux
>>               - "clkin1" - second parent clock of the internal mux
>>
>> +Optional properties on Meson8b and newer:
>> +- amlogic,tx-delay-ns:       The internal RGMII TX clock delay (provided
>> +                     by this driver) in nanoseconds. Allowed values
>> +                     are: 0ns, 2ns, 4ns, 6ns.
>> +                     This must be configured when the phy-mode is
>> +                     "rgmii" (typically a value of 2ns is used in
>> +                     this case).
>> +                     When phy-mode is set to "rgmii-id" or
>> +                     "rgmii-txid" the TX clock delay is already
>> +                     provided by the PHY. In that case this
>> +                     property should be set to 0ns (which disables
>> +                     the TX clock delay in the MAC to prevent the
>> +                     clock from going off because both PHY and MAC
>> +                     are adding a delay).
>
> What's the default? Why can't no property mean 0ns delay?
This value (2ns) was previously hardcoded. Having a default of 0ns
means that patch 7 ("ARM64: dts: amlogic: add the ethernet TX delay
configuration") becomes mandatory (otherwise we'll have broken Gbit
ethernet again because the TX delay is now disabled in the PHY when
phy-mode is "rgmii" and additionally we don't apply the 2ns TX delay
on the MAC side when the property is missing).
I'm fine with either way though - just let me know so I can adjust the
code accordingly.