Re: [PATCH net-next 00/11] net: macb: implement context swapping

[Nicolai Buchwitz]

On 1.4.2026 18:39, 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 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.

Thanks for your work, the context swapping approach probably
makes a lot of sense and will finally bring proper MTU change
support that I tried to patch earlier.

> 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@xxxxxxxxxxx/
> [1]: 
> https://lore.kernel.org/netdev/20260323221047.2749577-1-pvalerio@xxxxxxxxxx/
> [2]: 
> https://lore.kernel.org/netdev/20260304-macb-xsk-v1-0-ba2ebe2bdaa3@xxxxxxxxxxx/
>
> Signed-off-by: Théo Lebrun <theo.lebrun@xxxxxxxxxxx>
> ---
> Théo Lebrun (11):
>       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: introduce macb_context_alloc() helper
>       net: macb: use context swapping in .set_ringparam()
>       net: macb: use context swapping in .ndo_change_mtu()
>
>  drivers/net/ethernet/cadence/macb.h      |  119 +-
>  drivers/net/ethernet/cadence/macb_main.c | 1731 
> +++++++++++++++++-------------
>  drivers/net/ethernet/cadence/macb_pci.c  |   46 +-
>  drivers/net/ethernet/cadence/macb_ptp.c  |   26 +-
>  4 files changed, 1090 insertions(+), 832 deletions(-)
> ---
> base-commit: 321d1ee521de1362c22adadbc0ce066050a17783

The series didn't apply cleanly on current net-next. The
base commit 321d1ee521de doesn't seem to be upstream yet, is
this based on your set_channels v4 series?

> change-id: 20260401-macb-context-bd0caf20414d
>
> Best regards,
> --
> Théo Lebrun <theo.lebrun@xxxxxxxxxxx>

Thanks
Nicolai