Early DSA drivers were kind of simplistic in that they assumed a fairly
narrow hardware layout. User ports would have integrated PHYs at an
internal MDIO address that is derivable from the port number, and shared
(DSA and CPU) ports would have an MII-style (serial or parallel)
connection to another MAC. Phylib and then phylink were used to drive
the internal PHYs, and this needed little to no description through the
platform data structures. Bringing up the shared ports at the maximum
supported link speed was the responsibility of the drivers.

As a result of this, when these early drivers were converted from
platform data to the new DSA OF bindings, there was no link information
translated into the first DT bindings.

https://lore.kernel.org/all/YtXFtTsf++AeDm1l@lunn.ch/

Later, phylink was adopted for shared ports as well, and today we have a
workaround in place, introduced by commit a20f9970 ("net: dsa: Don't
instantiate phylink for CPU/DSA ports unless needed"). There, DSA checks
for the presence of phy-handle/fixed-link/managed OF properties, and if
missing, phylink registration would be skipped. This is because phylink
is optional for some drivers (the shared ports already work without it),
but the process of starting to register a port with phylink is
irreversible: if phylink_create() fails to find the fwnode properties it
needs, it bails out and it leaves the ports inoperational (because
phylink expects ports to be initially down, so DSA necessarily takes
them down, and doesn't know how to put them back up again).

DSA being a common framework, new drivers opt into this workaround
willy-nilly, but the ideal behavior from the DSA core's side would have
been to not interfere with phylink's process of failing at all. This
isn't possible because of regression concerns with pre-phylink DT blobs,
but at least DSA should put a stop to the proliferation of more of such
cases that rely on the workaround to skip phylink registration, and
sanitize the environment that new drivers work in.

To that end, create a list of compatible strings for which the
workaround is preserved, and don't apply the workaround for any drivers
outside that list (this includes new drivers).

In some cases, we make the assumption that even existing drivers don't
rely on DSA's workaround, and we do this by looking at the device trees
in which they appear. We can't fully know what is the situation with
downstream DT blobs, but we can guess the overall trend by studying the
DT blobs that were submitted upstream. If there are upstream blobs that
have lacking descriptions, we take it as very likely that there are many
more downstream blobs that do so too. If all upstream blobs have
complete descriptions, we take that as a hint that the driver is a
candidate for enforcing strict DT bindings (considering that most
bindings are copy-pasted). If there are no upstream DT blobs, we take
the conservative route of allowing the workaround, unless the driver
maintainer instructs us otherwise.

The driver situation is as follows:

ar9331
~~~~~~

    compatible strings:
    - qca,ar9331-switch

    1 occurrence in mainline device trees, part of SoC dtsi
    (arch/mips/boot/dts/qca/ar9331.dtsi), description is not problematic.

    Verdict: opt into strict DT bindings and out of workarounds.

b53
~~~

    compatible strings:
    - brcm,bcm5325
    - brcm,bcm53115
    - brcm,bcm53125
    - brcm,bcm53128
    - brcm,bcm5365
    - brcm,bcm5389
    - brcm,bcm5395
    - brcm,bcm5397
    - brcm,bcm5398

    - brcm,bcm53010-srab
    - brcm,bcm53011-srab
    - brcm,bcm53012-srab
    - brcm,bcm53018-srab
    - brcm,bcm53019-srab
    - brcm,bcm5301x-srab
    - brcm,bcm11360-srab
    - brcm,bcm58522-srab
    - brcm,bcm58525-srab
    - brcm,bcm58535-srab
    - brcm,bcm58622-srab
    - brcm,bcm58623-srab
    - brcm,bcm58625-srab
    - brcm,bcm88312-srab
    - brcm,cygnus-srab
    - brcm,nsp-srab
    - brcm,omega-srab

    - brcm,bcm3384-switch
    - brcm,bcm6328-switch
    - brcm,bcm6368-switch
    - brcm,bcm63xx-switch

    I've found at least these mainline DT blobs with problems:

    arch/arm/boot/dts/bcm47094-linksys-panamera.dts
    - lacks phy-mode
    arch/arm/boot/dts/bcm47189-tenda-ac9.dts
    - lacks phy-mode and fixed-link
    arch/arm/boot/dts/bcm47081-luxul-xap-1410.dts
    arch/arm/boot/dts/bcm47081-luxul-xwr-1200.dts
    arch/arm/boot/dts/bcm47081-buffalo-wzr-600dhp2.dts
    - lacks phy-mode and fixed-link
    arch/arm/boot/dts/bcm47094-luxul-xbr-4500.dts
    arch/arm/boot/dts/bcm4708-smartrg-sr400ac.dts
    arch/arm/boot/dts/bcm4708-luxul-xap-1510.dts
    arch/arm/boot/dts/bcm953012er.dts
    arch/arm/boot/dts/bcm4708-netgear-r6250.dts
    arch/arm/boot/dts/bcm4708-buffalo-wzr-1166dhp-common.dtsi
    arch/arm/boot/dts/bcm4708-luxul-xwc-1000.dts
    arch/arm/boot/dts/bcm47094-luxul-abr-4500.dts
    - lacks phy-mode and fixed-link
    arch/arm/boot/dts/bcm53016-meraki-mr32.dts
    - lacks phy-mode

    Verdict: opt into DSA workarounds.

bcm_sf2
~~~~~~~

    compatible strings:
    - brcm,bcm4908-switch
    - brcm,bcm7445-switch-v4.0
    - brcm,bcm7278-switch-v4.0
    - brcm,bcm7278-switch-v4.8

    A single occurrence in mainline
    (arch/arm64/boot/dts/broadcom/bcm4908/bcm4908.dtsi), part of a SoC
    dtsi, valid description. Florian Fainelli explains that most of the
    bcm_sf2 device trees lack a full description for the internal IMP
    ports.

    Verdict: opt the BCM4908 into strict DT bindings, and opt the rest
    into the workarounds. Note that even though BCM4908 has strict DT
    bindings, it still does not register with phylink on the IMP port
    due to it implementing ->adjust_link().

hellcreek
~~~~~~~~~

    compatible strings:
    - hirschmann,hellcreek-de1soc-r1

    No occurrence in mainline device trees. Kurt Kanzenbach explains
    that the downstream device trees lacked phy-mode and fixed link, and
    needed work, but were fixed in the meantime.

    Verdict: opt into strict DT bindings and out of workarounds.

lan9303
~~~~~~~

    compatible strings:
    - smsc,lan9303-mdio
    - smsc,lan9303-i2c

    1 occurrence in mainline device trees:
    arch/arm/boot/dts/imx53-kp-hsc.dts
    - no phy-mode, no fixed-link

    Verdict: opt out of strict DT bindings and into workarounds.

lantiq_gswip
~~~~~~~~~~~~

    compatible strings:
    - lantiq,xrx200-gswip
    - lantiq,xrx300-gswip
    - lantiq,xrx330-gswip

    No occurrences in mainline device trees. Martin Blumenstingl
    confirms that the downstream OpenWrt device trees lack a proper
    fixed-link and need work, and that the incomplete description can
    even be seen in the example from
    Documentation/devicetree/bindings/net/dsa/lantiq-gswip.txt.

    Verdict: opt out of strict DT bindings and into workarounds.

microchip ksz
~~~~~~~~~~~~~

    compatible strings:
    - microchip,ksz8765
    - microchip,ksz8794
    - microchip,ksz8795
    - microchip,ksz8863
    - microchip,ksz8873
    - microchip,ksz9477
    - microchip,ksz9897
    - microchip,ksz9893
    - microchip,ksz9563
    - microchip,ksz8563
    - microchip,ksz9567
    - microchip,lan9370
    - microchip,lan9371
    - microchip,lan9372
    - microchip,lan9373
    - microchip,lan9374

    5 occurrences in mainline device trees, all descriptions are valid.
    But we had a snafu for the ksz8795 and ksz9477 drivers where the
    phy-mode property would be expected to be located directly under the
    'switch' node rather than under a port OF node. It was fixed by
    commit edecfa98 ("net: dsa: microchip: look for phy-mode in port
    nodes"). The driver still has compatibility with the old DT blobs.
    The lan937x support was added later than the above snafu was fixed,
    and even though it has support for the broken DT blobs by virtue of
    sharing a common probing function, I'll take it that its DT blobs
    are correct.

    Verdict: opt lan937x into strict DT bindings, and the others out.

mt7530
~~~~~~

    compatible strings
    - mediatek,mt7621
    - mediatek,mt7530
    - mediatek,mt7531

    Multiple occurrences in mainline device trees, one is part of an SoC
    dtsi (arch/mips/boot/dts/ralink/mt7621.dtsi), all descriptions are fine.

    Verdict: opt into strict DT bindings and out of workarounds.

mv88e6060
~~~~~~~~~

    compatible string:
    - marvell,mv88e6060

    no occurrences in mainline, nobody knows anybody who uses it.

    Verdict: opt out of strict DT bindings and into workarounds.

mv88e6xxx
~~~~~~~~~

    compatible strings:
    - marvell,mv88e6085
    - marvell,mv88e6190
    - marvell,mv88e6250

    Device trees that have incomplete descriptions of CPU or DSA ports:
    arch/arm64/boot/dts/freescale/imx8mq-zii-ultra.dtsi
    - lacks phy-mode
    arch/arm64/boot/dts/marvell/cn9130-crb.dtsi
    - lacks phy-mode and fixed-link
    arch/arm/boot/dts/vf610-zii-ssmb-spu3.dts
    - lacks phy-mode
    arch/arm/boot/dts/kirkwood-mv88f6281gtw-ge.dts
    - lacks phy-mode
    arch/arm/boot/dts/vf610-zii-spb4.dts
    - lacks phy-mode
    arch/arm/boot/dts/vf610-zii-cfu1.dts
    - lacks phy-mode
    arch/arm/boot/dts/vf610-zii-dev-rev-c.dts
    - lacks phy-mode on CPU port, fixed-link on DSA ports
    arch/arm/boot/dts/vf610-zii-dev-rev-b.dts
    - lacks phy-mode on CPU port
    arch/arm/boot/dts/armada-381-netgear-gs110emx.dts
    - lacks phy-mode
    arch/arm/boot/dts/vf610-zii-scu4-aib.dts
    - lacks fixed-link on xgmii DSA ports and/or in-band-status on
      2500base-x DSA ports, and phy-mode on CPU port
    arch/arm/boot/dts/imx6qdl-gw5904.dtsi
    - lacks phy-mode and fixed-link
    arch/arm/boot/dts/armada-385-clearfog-gtr-l8.dts
    - lacks phy-mode and fixed-link
    arch/arm/boot/dts/vf610-zii-ssmb-dtu.dts
    - lacks phy-mode
    arch/arm/boot/dts/kirkwood-dir665.dts
    - lacks phy-mode
    arch/arm/boot/dts/kirkwood-rd88f6281.dtsi
    - lacks phy-mode
    arch/arm/boot/dts/orion5x-netgear-wnr854t.dts
    - lacks phy-mode and fixed-link
    arch/arm/boot/dts/armada-388-clearfog.dts
    - lacks phy-mode
    arch/arm/boot/dts/armada-xp-linksys-mamba.dts
    - lacks phy-mode
    arch/arm/boot/dts/armada-385-linksys.dtsi
    - lacks phy-mode
    arch/arm/boot/dts/imx6q-b450v3.dts
    arch/arm/boot/dts/imx6q-b850v3.dts
    - has a phy-handle but not a phy-mode?
    arch/arm/boot/dts/armada-370-rd.dts
    - lacks phy-mode
    arch/arm/boot/dts/kirkwood-linksys-viper.dts
    - lacks phy-mode
    arch/arm/boot/dts/imx51-zii-rdu1.dts
    - lacks phy-mode
    arch/arm/boot/dts/imx51-zii-scu2-mezz.dts
    - lacks phy-mode
    arch/arm/boot/dts/imx6qdl-zii-rdu2.dtsi
    - lacks phy-mode
    arch/arm/boot/dts/armada-385-clearfog-gtr-s4.dts
    - lacks phy-mode and fixed-link

    Verdict: opt out of strict DT bindings and into workarounds.

ocelot
~~~~~~

    compatible strings:
    - mscc,vsc9953-switch
    - felix (arch/arm64/boot/dts/freescale/fsl-ls1028a.dtsi) is a PCI
      device, has no compatible string

    2 occurrences in mainline, both are part of SoC dtsi and complete.

    Verdict: opt into strict DT bindings and out of workarounds.

qca8k
~~~~~

    compatible strings:
    - qca,qca8327
    - qca,qca8328
    - qca,qca8334
    - qca,qca8337

    5 occurrences in mainline device trees, none of the descriptions are
    problematic.

    Verdict: opt into strict DT bindings and out of workarounds.

realtek
~~~~~~~

    compatible strings:
    - realtek,rtl8366rb
    - realtek,rtl8365mb

    2 occurrences in mainline, both descriptions are fine, additionally
    rtl8365mb.c has a comment "The device tree firmware should also
    specify the link partner of the extension port - either via a
    fixed-link or other phy-handle."

    Verdict: opt into strict DT bindings and out of workarounds.

rzn1_a5psw
~~~~~~~~~~

    compatible strings:
    - renesas,rzn1-a5psw

    One single occurrence, part of SoC dtsi
    (arch/arm/boot/dts/r9a06g032.dtsi), description is fine.

    Verdict: opt into strict DT bindings and out of workarounds.

sja1105
~~~~~~~

    Driver already validates its port OF nodes in
    sja1105_parse_ports_node().

    Verdict: opt into strict DT bindings and out of workarounds.

vsc73xx
~~~~~~~

    compatible strings:
    - vitesse,vsc7385
    - vitesse,vsc7388
    - vitesse,vsc7395
    - vitesse,vsc7398

    2 occurrences in mainline device trees, both descriptions are fine.

    Verdict: opt into strict DT bindings and out of workarounds.

xrs700x
~~~~~~~

    compatible strings:
    - arrow,xrs7003e
    - arrow,xrs7003f
    - arrow,xrs7004e
    - arrow,xrs7004f

    no occurrences in mainline, we don't know.

    Verdict: opt out of strict DT bindings and into workarounds.

Because there is a pattern where newly added switches reuse existing
drivers more often than introducing new ones, I've opted for deciding
who gets to opt into the workaround based on an OF compatible match
table in the DSA core. The alternative would have been to add another
boolean property to struct dsa_switch, like configure_vlan_while_not_filtering.
But this avoids situations where sometimes driver maintainers obfuscate
what goes on by sharing a common probing function, and therefore making
new switches inherit old quirks.

Side note, we also warn about missing properties for drivers that rely
on the workaround. This isn't an indication that we'll break
compatibility with those DT blobs any time soon, but is rather done to
raise awareness about the change, for future DT blob authors.

Cc: Rob Herring <robh+dt@kernel.org>
Cc: Frank Rowand <frowand.list@gmail.com>
Acked-by: Alvin Šipraga <alsi@bang-olufsen.dk> # realtek
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>