linux-kernel - Re: [PATCH net-next 02/28] dt-bindings: net: fman: Add additional interface properties

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Date:   Fri, 17 Jun 2022 18:16:56 -0700
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Sean Anderson <sean.anderson@...o.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Madalin Bucur <madalin.bucur@....com>, netdev@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Paolo Abeni <pabeni@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        Eric Dumazet <edumazet@...gle.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org
Subject: Re: [PATCH net-next 02/28] dt-bindings: net: fman: Add additional
 interface properties

On 17/06/2022 13:32, 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. 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 1GBase-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 default address for the XFI PCS/PMA be the
> same as for SGMII. 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.
> 
> MEMACs (across all SoCs) support the following protocols:
> 
> - MII
> - RGMII
> - SGMII, 1000Base-X, and 1000Base-KX
> - 2500Base-X (aka 2.5G SGMII)
> - QSGMII
> - 10GBase-R (aka XFI) and 10GBase-KR
> - XAUI and HiGig
> 
> Each line documents a set of orthogonal protocols (e.g. XAUI is
> supported if and only if HiGig is supported). Additionally,
> 
> - XAUI implies support for 10GBase-R
> - 10GBase-R is supported if and only if RGMII is not supported
> - 2500Base-X implies support for 1000Base-X
> - MII implies support for RGMII
> 
> To switch between different protocols, we must reconfigure the SerDes.
> This is done by using the standard phys property. We can also use it to
> validate whether different protocols are supported (e.g. using
> phy_validate). This will work for serial protocols, but not RGMII or
> MII. Additionally, we still need to be compatible when there is no
> SerDes.
> 
> While we can detect 10G support by examining the port speed (as set by
> fsl,fman-10g-port), we cannot determine support for any of the other
> protocols based on the existing binding. In fact, the binding works
> against us in some respects, because pcsphy-handle is required even if
> there is no possible PCS/PMA for that MAC. To allow for backwards-
> compatibility, we use a boolean-style property for RGMII (instead of
> presence/absence-style). When the property for RGMII is missing, we will
> assume that it is supported. The exception is MII, since no existing
> device trees use it (as far as I could tell).
> 
> Unfortunately, QSGMII support will be broken for old device trees. There
> is nothing we can do about this because of the PCS/PMA situation (as
> described above).
> 
> Signed-off-by: Sean Anderson <sean.anderson@...o.com>

Thanks for the patch but you add too many new properties. The file
should be converted to YAML/DT schema first.


Best regards,
Krzysztof