[PATCH net-next v2 00/14] net: macb: implement context swapping

Théo Lebrun
2026-04-10T19:52:06Z

MACB has a pretty primitive approach to buffer management. They are all
stored in `struct macb *bp`. On operations that require buffer realloc
(set_ringparam & change_mtu ATM), the only option is to close the
interface, change our global state and re-open the interface.

Two issues:
- It doesn't fly on memory pressured systems; we free our precious
buffers and don't manage to reallocate fully, meaning our machine
just lost its network access.
- Anecdotally, it is pretty slow because it implies a full PHY reinit.

Instead, we shall:
- allocate a new context (including buffers) first
- if it fails, early return without any impact to the interface
- stop interface
- update global state (bp, netdev, etc)
- pass newly allocated buffer pointers to the hardware
- start interface
- free old context

This is what we implement here. Both .set_ringparam() and
.ndo_change_mtu() are covered by this series. In the future,
at least .set_channels() [0], XDP [1] and XSK [2] would benefit.

The change is super intrusive so conflicts will be major. Sorry!

Thanks,
Have a nice day,
Théo

[0]: https://lore.kernel.org/netdev/20260317-macb-set-channels-v4-0-1bd4f4ffcfca@bootlin.com/
[1]: https://lore.kernel.org/netdev/20260323221047.2749577-1-pvalerio@redhat.com/
[2]: https://lore.kernel.org/netdev/20260304-macb-xsk-v1-0-ba2ebe2bdaa3@bootlin.com/

Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
---
Changes in v2:
- Patch "add subset of `struct macb` to `struct macb_context`" was
messed up. It contained much more than what the name implied. Split
into three commits (I caused trouble by rebase reordering).
- Fix tieoff; V1 allocated it without initialisation.
- Fix NULL pointer dereference on context in mab_get_regs() and
macb_get_ringparam() when interface is offline.
- Patch "unify device pointer naming convention":
- Fix build issue when CONFIG_NETCONSOLE=y.
- Rename `struct net_device *dev` to `netdev` in macb.h.
- Rename `struct phy_device *phy` to `phydev` in macb_main.c.
- On swap, call netdev_tx_reset_queue() to reset all DQL counters.
- At end of swap, add missing kfree(old_ctx).
- During HW disabling in swap, grab bp->lock to protect against IRQ
handler.
- On swap, cancel the three BH features MACB has:
bp->hresp_err_bh_work, bp->tx_lpi_work and queue->tx_error_task.
- On swap, call macb_configure_dma() which writes buffer size to
hardware registers. This is important because the change_mtu codepath
changes the buffer size.
- Rebase onto latest net-next/main (58dd34dbd5b0) & resolve conflicts.
- Link to v1: https://patch.msgid.link/20260401-macb-context-v1-0-9590c5ab7272@bootlin.com

---
Théo Lebrun (14):
net: macb: unify device pointer naming convention
net: macb: unify `struct macb *` naming convention
net: macb: unify queue index variable naming convention and types
net: macb: enforce reverse christmas tree (RCT) convention
net: macb: allocate tieoff descriptor once across device lifetime
net: macb: introduce macb_context struct for buffer management
net: macb: avoid macb_init_rx_buffer_size() modifying state
net: macb: make `struct macb` subset reachable from macb_context struct
net: macb: change caps helpers signatures
net: macb: change function signatures to take contexts
net: macb: introduce macb_context_alloc() helper
net: macb: re-read ISR inside IRQ handler locked section
net: macb: use context swapping in .set_ringparam()
net: macb: use context swapping in .ndo_change_mtu()

drivers/net/ethernet/cadence/macb.h | 125 ++-
drivers/net/ethernet/cadence/macb_main.c | 1767 +++++++++++++++++-------------
drivers/net/ethernet/cadence/macb_pci.c | 46 +-
drivers/net/ethernet/cadence/macb_ptp.c | 26 +-
4 files changed, 1126 insertions(+), 838 deletions(-)
---
base-commit: 6b6916526425235d5875df21dfa6f31fdc098599
change-id: 20260401-macb-context-bd0caf20414d

Best regards,
--
Théo Lebrun <theo.lebrun@bootlin.com>