Re: [PATCH net-next v4 07/15] net: macb: introduce macb_context struct for buffer management

Hi Théo

On 17.7.2026 21:48, Théo Lebrun wrote:

Whenever an operation requires buffer realloc, we close the interface,
update parameters and reopen. To improve reliability under memory
pressure, we should rather alloc new buffers, reconfigure HW and free
old buffers. This requires MACB to support having multiple "contexts"
in parallel.

Introduce this concept by adding the macb_context struct, which owns 
all
queue buffers and the parameters associated. We do not yet support
multiple contexts in parallel, because all functions access bp->ctx
(the currently active context) directly.

Steps:

 - Introduce `struct macb_context` and its children `struct macb_rxq`
   and `struct macb_txq`. Context fields are stolen from `struct macb`
   and rxq/txq fields are from `struct macb_queue`.

   Making it two separate structs per queue simplifies accesses: we 
grab
   a txq/rxq local variable and access fields like txq->head instead of
   queue->tx_head. It also anecdotally improves data locality.

 - macb_init_dflt() / macb_get_ringparam() do not access
   bp->ctx->{rx,tx}_ring_size as they will/might run while interface is
   offline and ctx is not NULL. Instead, introduce
   bp->configured_{rx,tx}_ring_size which get updated on user requests.

nit: In the commit message: "ctx is not NULL" should be "ctx is NULL".

 - macb_open() starts by allocating bp->ctx. It gets freed in the
   open error codepath or by macb_close().

 - Guided by compile errors, update all codepaths. Most diff is 
changing
   `queue->tx_*` to `txq->*` and `queue->rx_*` to `rxq->*`, with a new
   local variable. Also rx_buffer_size / rx_ring_size / tx_ring_size
   move from bp to bp->ctx.

   Introduce two helpers macb_txq|rxq() functions to convert macb_queue
   pointers.

 - macb_get_regs() is tweaked to support being ran while interface is
   offline (and context is NULL). Use default values at zero and
   override them only if context is present.

Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
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[...]

Reviewed-by: Nicolai Buchwitz <redacted>

Thanks,
Nicolai