netdev - Re: [PATCH 1/2] Documentation: devicetree: clarify usage of the RGMII phy-modes

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Date:   Sat, 26 Nov 2016 21:53:47 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        robh+dt@...nel.org, mark.rutland@....com, davem@...emloft.net,
        sean.wang@...iatek.com, netdev@...r.kernel.org,
        devicetree@...r.kernel.org
Cc:     linux-amlogic@...ts.infradead.org, jbrunet@...libre.com
Subject: Re: [PATCH 1/2] Documentation: devicetree: clarify usage of the RGMII
 phy-modes



On 11/25/2016 05:12 AM, Martin Blumenstingl wrote:
> RGMII requires special RX and/or TX delays depending on the actual
> hardware circuit/wiring. These delays can be added by the MAC, the PHY
> or the designer of the circuit (the latter means that no delay has to
> be added by PHY or MAC).
> There are 4 RGMII phy-modes used describe where a delay should be
> applied:
> - rgmii: the RX and TX delays are either added by the MAC (where the
>   exact delay is typically configurable, and can be turned off when no
>   extra delay is needed) or not needed at all (because the hardware
>   wiring adds the delay already). The PHY should neither add the RX nor
>   TX delay in this case.
> - rgmii-rxid: configures the PHY to enable the RX delay. The MAC should
>   not add the RX delay in this case.
> - rgmii-txid: configures the PHY to enable the TX delay. The MAC should
>   not add the TX delay in this case.
> - rgmii-id: combines rgmii-rxid and rgmii-txid and thus configures the
>   PHY to enable the RX and TX delays. The MAC should neither add the RX
>   nor TX delay in this case.
> 
> Document these cases in the ethernet.txt documentation to make it clear
> when to use each mode.
> If applied incorrectly one might end up with MAC and PHY both enabling
> for example the TX delay, which breaks ethernet TX traffic on 1000Mbit/s
> links.
> 
> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@...glemail.com>

Reviewed-by: Florian Fainelli <f.fainelli@...il.com>
-- 
Florian