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

[Sean Anderson]

Hi Krzysztof,

On 6/17/22 9:16 PM, Krzysztof Kozlowski wrote:
> 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@xxxxxxxx>
>
> Thanks for the patch but you add too many new properties. The file
> should be converted to YAML/DT schema first.

Perhaps. However, conversion to yaml is a non-trivial task, especially for
a complicated binding such as this one. I am more than happy to rework this
patch to be based on a yaml conversion, but I do not have the bandwidth to
do so myself.

If you have any comments on the binding changes themselves, that would be
much appreciated.

--Sean