Re: [PATCH net-next v11 0/9] net: macb: implement context swapping

Hi Théo

On 13.10.2026 15:16, Théo Lebrun wrote:

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 at the moment), 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.

[...]

Tested on a Raspberry Pi CM5 (RP1 GEM) with lockdep and KASAN enabled:

- ring and MTU changes under bidirectional TCP and a UDP flood
- ring and MTU changes while the interface is down
- ring and MTU changes during autoneg
- injected allocation failures in both paths
- PTP and EEE after a swap

Everything worked, and changing either no longer takes the link down.

For the series:

Tested-by: Nicolai Buchwitz <nb@tipi-net.de> # RPi CM5 with RP1 GEM

Thanks,
Nicolai