Messages in this thread | | | Date | Sat, 9 Sep 2023 22:53:46 +0300 | Subject | Re: [PATCH 2/4] dt-bindings: net: dsa: document internal MDIO bus | From | Arınç ÜNAL <> |
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On 9.09.2023 11:53, Arınç ÜNAL wrote: > On 4.09.2023 14:33, Arınç ÜNAL wrote: >> Hey Vladimir, >> >> On 27.08.2023 15:12, Vladimir Oltean wrote: >>> Hi Arınç, >>> >>> I am on vacation and I will just reply with some clarification aspects, >>> without having done any further research on the topic since my last reply. >>> >>> On Sun, Aug 27, 2023 at 11:33:16AM +0300, Arınç ÜNAL wrote: >>>> Before I continue commenting, I'd like to state my understanding so we can >>>> make sure we're on the same page. If a driver doesn't use >>>> ds->slave_mii_bus, the switch it controls must not have any internal MDIO >>>> buses. Otherwise the PHYs on these buses couldn't function, and an improper >>>> driver like this would not be on the official Linux source code. >>> >>> A DSA switch port, like any OF-based ethernet-controller which uses >>> phylink, will use one of the phy-handle, fixed-link or managed properties >>> to describe the interface connecting the MAC/MAC-side PCS to the PHY. >>> >>> At its core, ds->slave_mii_bus is nothing more than a mechanism to make >>> sense of device trees where the above 3 phylink properties are not present. >>> >>> It is completely false to say that if a driver doesn't have ds->slave_mii_bus, >>> it must not have an internal MDIO bus. Because you could still describe >>> that internal MDIO bus like below, without making any use of the sole property >>> that makes ds->slave_mii_bus useful from a dt-bindings perspective. >>> >>> ethernet-switch { >>> ethernet-ports { >>> port@0 { >>> reg = <0>; >>> phy-handle = <&port0_phy>; >>> phy-mode = "internal"; >>> }; >>> }; >>> >>> mdio { >>> port0_phy: ethernet-phy@0 { >>> reg = <0>; >>> }; >>> }; >>> }; >>> >>> This is the more universal way of describing the port setup in an >>> OF-based way. There is also the DSA-specific (and old-style, before phylink) >>> way of describing the same thing, which relies on the non-OF-based >>> ds->slave_mii_bus, with bindings that look like this: >>> >>> ethernet-switch { >>> ethernet-ports { >>> port@0 { >>> reg = <0>; >>> }; >>> }; >>> }; >>> >>> But, I would say that the first variant of the binding is preferable, >>> since it is more universal. >>> >>> Not all switches that have an internal MDIO bus support the second >>> variant of the dt-binding (the ones that don't have ds->slave_mii_bus don't). >>> But, they support the same configuration through the first form. >> >> Understood. >> >>> >>> Furthermore, on the U-Boot mailing lists, I have been suggesting that >>> the DM_DSA driver for mv88e6xxx should not bother to support the second >>> version of the binding, since it is just more code to be added to handle >>> a case which can already be described with the more universal first binding. >> >> That makes sense. >> >>> >>>> I've checked mscc,vsc7514-switch. What I see is, the architecture is an SoC >>>> with a switch component. Since the switch component is not designed to be a >>>> standalone IC, the MDIO bus of the SoC could just as well be used without >>>> the need to design an MDIO controller specific to the switch component, to >>>> manage the PHYs. So I see this switch as just another case of a switch >>>> without an internal MDIO bus. >>> >>> Well, we need to clarify the semantics of an "internal" MDIO bus. >>> >>> I would say most discrete chips with DSA switches have this SoC-style >>> architecture, with separate address spaces for the switching IP, MDIO >>> bus, GPIO controller, IRQ controllers, temperature sensors etc (see >>> "mscc,vsc7512-switch" which is like "mscc,vsc7514-switch", but it is >>> controlled over SPIO instead of MMIO). The dt-bindings of most DSA >>> switches may or may not reflect that discrete chip organization. Those >>> drivers and dt-bindings could be reimagined so that DSA is not the >>> top-level driver. >>> >>> Yet, I would argue that it's wrong to say that because it isn't an OF >>> child of the switch, the MDIO bus of the VSC7514 is not internal in the >>> same way that the Realtek MDIO bus is internal. The switch ports are >>> connected to internal PHYs on this MDIO bus, and there aren't PHYs on >>> this MDIO bus that go to other MACs than the switch ports. So, the >>> VSC7514 MDIO bus could legally be called the internal MDIO bus of the >>> switch, even if there isn't a parent/child relationship between them. >> >> Good point, I had believed that the management interface of all of the PHYs >> being connected to the MDIO bus - which is not part of the switching IP >> address space - would be enough to classify the MDIO bus as non-internal. >> >> However, the architecture of separate address spaces for the switching IP >> and MDIO bus is used on any type of IC with the switching feature. >> Therefore, this characteristic cannot be used to distinguish whether an >> MDIO bus is of a switch. >> >> What we can refer to to classify an internal MDIO bus is by confirming the >> data interface of all PHYs on the MDIO bus is connected to the switch port >> MACs, as you have pointed out here. >> >> Because the architecture of separate address spaces for the switching IP >> and MDIO bus is used on any type of IC with the switching feature, it can >> differ by driver how the MDIO bus is defined on the dt-bindings. So we >> can't make universal bindings of an internal MDIO bus of a switch that >> apply to every switch. >> >> So, the correct approach is to define things under the switch-specific >> schema which is affine to the driver, as you have already pointed out. >> Which schemas to define what will of course differ. >> >>> >>> So, what I'm disagreeing with is your insistence to correlate your >>> problem with internal MDIO buses. The way in which the problem is >>> formulated dictates what problem gets solved, and the problem is not >>> correctly formulated here. It is purely about ds->slave_mii_bus and its >>> driver-defined OF presence/absence. It is a DSA-specific binding aspect >>> which not even all DSA switches inherit, let alone bindings outside DSA. >> >> Got it. >> >>> >>>>> For switches in the second category, it all depends on the way in which >>>>> the driver finds the node for of_mdiobus_register(). >>>> >>>> Ok, so some drivers require the mdio child node. Some require it and the >>>> compatible property with a certain string. >>>> >>>> MDIO controlled Realtek switches do not need the compatible property under >>>> the mdio child node. There're no compatible strings to make a distinction >>>> between the SMI and MDIO controlled switches so the best we can do is keep >>>> it the way it currently is. Define realtek,smi-mdio as a compatible string >>>> but keep the compatible property optional. I did state this on my reply to >>>> patch 3 but still received reviewed-bys regardless. >>> >>> Yes, because.... [1] >>> >>>>> Having identified all switches which make some sort of use of >>>>> ds->slave_mii_bus, the rule would sound like this: >>>>> >>>>> 1. If the schema is that of (need to replace this with compatible >>>>> strings, I'm too lazy for that): >>>>> >>>>> - ksz_switch_ops >>>>> - mv88e6060_switch_ops >>>>> - lan9303_switch_ops >>>>> - rtl8365mb_switch_ops_mdio >>>>> - b53_switch_ops >>>>> - vsc73xx_ds_ops >>>>> - mv88e6xxx >>>>> - qca8k >>>>> >>>>> and we have an "mdio" child, then phylink bindings are mandatory on user ports. >>>>> >>>>> 2. If the schema is that of gswip_mdio and we have a child node of "lantiq,xrx200-mdio", >>>>> then phylink bindings are mandatory on user ports (I haven't checked, >>>>> but it might be that the "lantiq,xrx200-mdio" child is mandatory, and >>>>> in that case, this goes to category 4 below). >>>>> >>>>> 3. If the schema is that of realtek_smi_setup_mdio and we have a child node of >>>>> "realtek,smi-mdio", then phylink bindings are mandatory on user ports >>>>> (same comment about the child MDIO note maybe being mandatory). >>>>> >>>>> 4. If the switch didn't appear in the above set of rules, then phylink >>>>> bindings are unconditionally mandatory on user ports. >>>>> >>>>> We don't care at all what the drivers that don't use ds->slave_mii_bus >>>>> do with the "mdio" child node. It doesn't change the fact that their >>>>> user ports can't have missing phylink bindings. >>>> >>>> I partially agree. I say, for the switches without an internal MDIO bus, >>>> invalidate the mdio child node, and enforce the phylink bindings on the >>>> user ports. Such as mscc,vsc7514-switch and nxp,sja1105x. For nxp,sja1110x, >>>> invalidate the mdio child node, and enforce the phylink bindings on the >>>> user ports if the mdios property is used. >>> >>> Why "if the mdios property is used" and not "always"? :-/ >>> >>> To say it again: because the sja1105 driver does not use ds->slave_mii_bus, >>> it can make no sense of dt-bindings on user ports which lack phylink properties. >>> So they are *always* needed. The "mdios" property changes nothing in that regard. >> >> Got it. >> >>> >>>> >>>> I'd like to add this before I conclude. The way I understand dt-bindings is >>>> that a binding does not have to translate to an action on the driver. >>>> Documenting bindings for the sole purpose of describing hardware is a valid >>>> case. >>> >>> [1] ...this. The SMI-controlled and MDIO-controlled Realtek switches are >>> otherwise the same, right? So why would they have different dt-bindings? >> >> Honestly, I'm wondering the answer to this as well. For some reason, when >> probing the SMI controlled Realtek switches, instead of just letting >> dsa_switch_setup() populate ds->slave_mii_bus, on realtek_smi_setup_mdio() >> on realtek-smi.c: >> >> - priv->slave_mii_bus is allocated. >> - mdio_np = of_get_compatible_child(priv->dev->of_node, "realtek,smi-mdio"); >> - priv->slave_mii_bus->dev.of_node = mdio_np; >> - ds->slave_mii_bus = priv->slave_mii_bus; >> >>> >>>> For example, currently, the MT753X DSA subdriver won't, in any way, >>>> register the bus OF-based. Still, the mdio property for the switches which >>>> this driver controls can be documented because the internal mdio bus does >>>> exist on the hardware. >>> >>> It can, but the whole point is: if ds->slave_mii_bus gains an OF presence, >>> then it loses its core functionality (that user ports can lack phylink >>> bindings). This is the entire essence of what this discussion should capture. >> >> Understood. >> >>> >>>> >>>> So I'd like to keep the mdio property valid for the switches which their >>>> drivers can only register non-OF-based ds->slave_mii_bus. >>>> >>>> In conclusion, what to do: >>>> >>>> - Define "the mdio property" and "the enforcement of phylink bindings for >>>> user ports if mdio property is used" on ethernet-switch.yaml. >>>> - Invalidate the mdio property on the switches without an internal MDIO >>>> bus. >>>> - Define "the enforcement of phylink bindings for user ports" on the >>>> switches without an internal MDIO bus. >>>> - Require "the mdio property" for the switches which their driver requires >>>> it to function. >>>> - Require "the mdio property" and "the compatible string of the mdio >>>> property" for the switches which their driver requires them to function. >>>> >>>> There's no 1:1 switch to switch compatible string relation, as seen on >>>> Realtek switches so I'll have to figure that out as I go. >>>> >>>> I'm open to your comments to this mail but the gap between discussion and >>>> end result has widened a lot on this patch series so I'd like to first >>>> offload this conversation by preparing v2 with what I said here and discuss >>>> further there. >>> >>> Honestly, from my side, a verbal comment in the dt-bindings document >>> would have been just fine, as long as it is truthful to the reality it >>> describes. >>> >>> You wanted to over-complicate things with an actual schema validation, >>> and then hooking onto things that are unrelated with the phenomenon that >>> needs to be captured (like the "mdio" child node, without explicit >>> regard to whether it is the ds->slave_mii_bus or not). >>> >>> It's not about internal MDIO buses in general, it's about whether those >>> internal MDIO buses are used in ds->slave_mii_bus, and their OF >>> presence/absence! That is absolutely driver-specific and I would only >>> expect a driver-specific way of enforcing it. I didn't say it's not >>> hard, and I didn't ask to enforce it, either. >> >> OK, I believe we're on the same page now, I will start working on properly >> enforcing this. > > I'm writing below as a mix of patch log and discussion. > > Phylink bindings are required for ports that are controlled by OF-based > buses. DSA, like any other driver utilising the Linux MDIO infrastructure, > can register a bus. If I understand correctly, non-OF-based registration of > OpenFirmware MDIO buses is a feature specific to DSA which certain DSA > subdrivers make use of. > > There's no way to distinguish which port is controlled by which driver's > MDIO bus on the bindings so we can't enforce phylink bindings for all user > ports as this would also enforce phylink bindings on user ports controlled > by a non-OF-based bus. > > But we can know when DSA won't create a non-OF-based bus. That leaves us > with only OF-based buses in which case we can enforce phylink bindings for > all user ports. So we need to check each DSA subdriver to see when all > buses will be OF-based.
We also need to decide the phylink bindings for user ports.
Phylink bindings for CPU and DSA ports:
allOf: - required: - phy-mode - oneOf: - required: - fixed-link - required: - phy-handle - required: - managed
On one of the mscc,ocelot.yaml examples, "phy-handle" and "managed" are defined on the same user port. Assuming the example is correct, we must allow more than 1 of these properties to be used at the same time for user ports.
We need to at least allow "phy-handle" and "managed" to be used at the same time. Does "managed" also depend on "phy-handle"?
For example:
oneOf: - required: - fixed-link - anyOf: - required: - phy-handle - required: - managed
dependencies: managed: [ phy-handle ]
Arınç
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