[PATCH net-next v10 0/3] net: stmmac: dwxgmac2: timestamp interrupt support + Agilex5 fix

[Zxyan Zhu <zxyan0222@gmail.com>]

This series adds auxiliary snapshot (EXTTS) interrupt support to
DWXGMAC2/DWXLGMAC2, fixes a stale TSIS race on the Agilex5
cross-timestamp path that the new handler would otherwise expose, and
guards the shared aux snapshot handler against a zero channel mask.

Patch 1 makes smtg_crosststamp() complete on the persistent ATSNS
count instead of the transient TSIS bit, waits for the FIFO clear to
complete, and holds aux_ts_lock across the whole trigger/poll/drain
sequence so a concurrent EXTTS request cannot flush the snapshot FIFO
mid-flight.

Patch 2 guards the shared aux snapshot handler against a zero channel
mask: ilog2() is applied to the mask without a zero check, and
ilog2(0) yields an out-of-range event index that ptp_clock_event()
feeds to test_bit() unchecked from hard IRQ context.

Patch 3 adds a dedicated DWXGMAC2 timestamp interrupt handler.  The
XGMAC hwif entries used the generic ops, whose callback read the wrong
register and whose enable mask omitted the timestamp interrupt, so the
clock advertised the aux snapshot channels but no event was ever
delivered.  XGMAC_TSIE is not enabled by default; it is armed on demand
from the EXTTS enable/disable path through a new callback, and the
handler only touches the FIFO while the interrupt is armed and while no
cross-timestamp owns it.  The interrupt is disarmed on suspend and
unregister and re-armed on resume.

The failure fixed by patch 3 was hit while bringing up auxiliary
snapshot interrupts on a local DWXGMAC2 board (not Agilex5-class):
enabling an EXTTS channel succeeded but no PTP_CLOCK_EXTTS event ever
arrived.  After the change the same board delivers EXTTS events on the
enabled channel.  The races fixed by patches 1 and 2 were found by
reviewing the code paths that this bring-up exposed; they are narrow
race windows and were not reproduced on hardware in isolation.

---

v1: https://lore.kernel.org/netdev/20260806-dwxgmac2-timestamp-irq-v1-1-c051c79c9d90@gmail.com/
v2: https://lore.kernel.org/netdev/20260810100221.9166-1-zxyan0222@gmail.com/
v3: https://lore.kernel.org/netdev/20260818132722.1852876-1-zxyan0222@gmail.com/
v4: https://lore.kernel.org/netdev/20260902131441.322167-1-zxyan0222@gmail.com/
v5: https://lore.kernel.org/netdev/20260910081020.86227-1-zxyan0222@gmail.com/
v6: https://lore.kernel.org/netdev/20260929073553.4136336-1-zxyan0222@gmail.com/
v7: https://lore.kernel.org/netdev/20261004120526.2728564-1-zxyan0222@gmail.com/
v8: https://lore.kernel.org/netdev/20261013033207.1684328-1-zxyan0222@gmail.com/
v9: https://lore.kernel.org/netdev/20261104125030.1183146-1-zxyan0222@gmail.com/

v10:
- Rebase on net-next from 2026-11-09 (containing 7.4-rc2, which moves
  the est_lock initialisation next to the aux_ts_lock one).
- Wrap two lines that exceeded 80 columns.

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2.34.1