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

[Florian Fainelli]

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 at googlemail.com>

Reviewed-by: Florian Fainelli <f.fainelli at gmail.com>
-- 
Florian