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

[Nicolai Buchwitz]

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@xxxxxxxxxxx> # RPi CM5 with RP1 GEM

Thanks,
Nicolai