[PATCH net-next v5 0/3] net: phylink: wait for a PHY that probes after the MAC

[Aleksei Sviridkin <f@lex.la>]

On the Keenetic KN-1012 (MT7981B with an MT7531 switch), the Airoha
EN8811H behind lan4 has its PHY driver built as a module on the root
filesystem. The switch sets up its ports before that filesystem is
mounted, so the port is validated against the generic driver, fails its
phy-mode and stays dead for the uptime. DSA does not retry it.

Patch 1 lets the PHY node say so with needs-host-firmware. Patch 2 makes
phylink poll for such a PHY instead of giving up, for a MAC that opts
in. Patch 3 opts in DSA user ports of switch drivers that set a flag,
and sets it in mt7530.

The poller can still lose a race against an unbind of the PHY driver,
between its readiness check and the attach. That window is phylib's:
any phy_attach_direct() caller racing an unbind has it. The attach
guard series [1] closes it.

Tested on that board with the series backported to its OpenWrt 6.18
kernel, together with a940003f44e7 and 07d995873960 (the mt7530
.get_stats64 atomic-context fix). The debug kernel used here wedges a
CPU without that fix, unrelated to this series. Two local debug
parameters, not part of the series, drove the error paths. One fails
the connect after a successful attach a given number of times, the
other ignores the opt-in.

 - boot: the switch set up its ports at 3.2 s, the PHY driver loaded
   its firmware at 8.7 s and lan4 attached at 9.5 s. Link up at 1 Gb/s.
 - opt-in ignored: the old behaviour. The generic driver took the PHY
   at switch setup and the port never polled.
 - two injected failures: "failed to connect late PHY: -EIO" twice, a
   second apart, and the third attempt attached. Link up at 1 Gb/s.
 - failures that do not stop: four attempts, then one "giving up on
   /soc/ethernet@15100000/mdio-bus/ethernet-phy@d after 4 attempts",
   and no further poll in the 25 s that followed.
 - switch unbound while the poller waited: the poll stopped, nothing
   oopsed, and the port attached normally after a rebind.

No in-tree device tree sets needs-host-firmware yet. The board is
supported out of tree, in OpenWrt.

Changes in v5 (since v4):
https://lore.kernel.org/r/20260925001209.2334139-1-f@lex.la/
 - Deferral is opt-in. A deferred connect returns 0 with no PHY
   attached, and some callers read 0 as a PHY being there. A MAC opts
   in with phylink_config.phy_may_probe_late. DSA sets it for user
   ports of drivers that set dsa_switch.phy_may_probe_late, and mt7530
   does (new patch 3).
 - Defer only with a known interface mode. The poller no longer fills
   in PHY_INTERFACE_MODE_NA, so the MAC is never started with NA.
 - kernel-doc names the opt-in and the state after the retries run out.
 - Rebased onto current net-next. Patch 1 is unchanged, Acked-by added.

[1] https://lore.kernel.org/r/20261001130120.104628-1-f@lex.la/

Aleksei Sviridkin (3):
  dt-bindings: net: ethernet-phy: add needs-host-firmware
  net: phylink: wait for PHYs that are known to probe late
  net: dsa: let user ports wait for a PHY that probes late

 .../devicetree/bindings/net/ethernet-phy.yaml |   6 +
 drivers/net/dsa/mt7530.c                      |   1 +
 drivers/net/phy/phylink.c                     | 221 +++++++++++++++++-
 include/linux/phylink.h                       |   4 +
 include/net/dsa.h                             |   5 +
 net/dsa/user.c                                |   1 +
 6 files changed, 230 insertions(+), 8 deletions(-)


base-commit: 47a1446725732cd3996edf607e8739334bbf4d78
-- 
2.53.0