linux-kernel - Re: [PATCH net-next v4 2/8] dt-bindings: net: fman: Add additional interface properties

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Date:   Mon, 22 Aug 2022 12:45:59 -0500
From:   Rob Herring <robh@...nel.org>
To:     Sean Anderson <sean.anderson@...o.com>
Cc:     Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
        netdev@...r.kernel.org, "David S . Miller" <davem@...emloft.net>,
        devicetree@...r.kernel.org,
        "linuxppc-dev @ lists . ozlabs . org" <linuxppc-dev@...ts.ozlabs.org>,
        Russell King <linux@...linux.org.uk>,
        linux-kernel@...r.kernel.org,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Madalin Bucur <madalin.bucur@....com>,
        linux-arm-kernel@...ts.infradead.org,
        Camelia Alexandra Groza <camelia.groza@....com>,
        Rob Herring <robh+dt@...nel.org>
Subject: Re: [PATCH net-next v4 2/8] dt-bindings: net: fman: Add additional
 interface properties

On Thu, 04 Aug 2022 15:46:59 -0400, Sean Anderson wrote:
> At the moment, mEMACs are configured almost completely based on the
> phy-connection-type. That is, if the phy interface is RGMII, it assumed
> that RGMII is supported. For some interfaces, it is assumed that the
> RCW/bootloader has set up the SerDes properly. This is generally OK, but
> restricts runtime reconfiguration. The actual link state is never
> reported.
> 
> To address these shortcomings, the driver will need additional
> information. First, it needs to know how to access the PCS/PMAs (in
> order to configure them and get the link status). The SGMII PCS/PMA is
> the only currently-described PCS/PMA. Add the XFI and QSGMII PCS/PMAs as
> well. The XFI (and 10GBASE-KR) PCS/PMA is a c45 "phy" which sits on the
> same MDIO bus as SGMII PCS/PMA. By default they will have conflicting
> addresses, but they are also not enabled at the same time by default.
> Therefore, we can let the XFI PCS/PMA be the default when
> phy-connection-type is xgmii. This will allow for
> backwards-compatibility.
> 
> QSGMII, however, cannot work with the current binding. This is because
> the QSGMII PCS/PMAs are only present on one MAC's MDIO bus. At the
> moment this is worked around by having every MAC write to the PCS/PMA
> addresses (without checking if they are present). This only works if
> each MAC has the same configuration, and only if we don't need to know
> the status. Because the QSGMII PCS/PMA will typically be located on a
> different MDIO bus than the MAC's SGMII PCS/PMA, there is no fallback
> for the QSGMII PCS/PMA.
> 
> Signed-off-by: Sean Anderson <sean.anderson@...o.com>
> ---
> 
> (no changes since v3)
> 
> Changes in v3:
> - Add vendor prefix 'fsl,' to rgmii and mii properties.
> - Set maxItems for pcs-names
> - Remove phy-* properties from example because dt-schema complains and I
>   can't be bothered to figure out how to make it work.
> - Add pcs-handle as a preferred version of pcsphy-handle
> - Deprecate pcsphy-handle
> - Remove mii/rmii properties
> 
> Changes in v2:
> - Better document how we select which PCS to use in the default case
> 
>  .../bindings/net/fsl,fman-dtsec.yaml          | 53 ++++++++++++++-----
>  .../devicetree/bindings/net/fsl-fman.txt      |  5 +-
>  2 files changed, 43 insertions(+), 15 deletions(-)
> 

Reviewed-by: Rob Herring <robh@...nel.org>