[PATCH net-next 10/11] net: macb: use context swapping in .set_ringparam()

Théo Lebrun
2026-04-01T16:39:49Z

ethtool_ops.set_ringparam() is implemented using the primitive close /
update ring size / reopen sequence. Under memory pressure this does not
fly: we free our buffers at close and cannot reallocate new ones at
open. Also, it triggers a slow PHY reinit.

Instead, exploit the new context mechanism and improve our sequence to:
- 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 buffer pointers to the hardware
- start interface
- free old context.

The HW disable sequence is inspired by macb_reset_hw() but avoids
(1) setting NCR bit CLRSTAT and (2) clearing register PBUFRXCUT.

The HW re-enable sequence is inspired by macb_mac_link_up(), skipping
over register writes which would be redundant (because values have not
changed).

The generic context swapping parts are isolated into helper functions
macb_context_swap_start|end(), reusable by other operations (change_mtu,
set_channels, etc).

Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
---
drivers/net/ethernet/cadence/macb_main.c | 89 +++++++++++++++++++++++++++++---
1 file changed, 82 insertions(+), 7 deletions(-)

diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
index 42b19b969f3e..543356554c11 100644
--- a/drivers/net/ethernet/cadence/macb_main.c
+++ b/drivers/net/ethernet/cadence/macb_main.c
@@ -2905,6 +2905,76 @@ static struct macb_context *macb_context_alloc(struct macb *bp,
return ctx;
}

+static void macb_context_swap_start(struct macb *bp)
+{
+ struct macb_queue *queue;
+ unsigned int q;
+ u32 ctrl;
+
+ /* Disable software Tx, disable HW Tx/Rx and disable NAPI. */
+
+ netif_tx_disable(bp->netdev);
+
+ ctrl = macb_readl(bp, NCR);
+ macb_writel(bp, NCR, ctrl & ~(MACB_BIT(RE) | MACB_BIT(TE)));
+
+ macb_writel(bp, TSR, -1);
+ macb_writel(bp, RSR, -1);
+
+ for (q = 0, queue = bp->queues; q < bp->num_queues; ++q, ++queue) {
+ queue_writel(queue, IDR, -1);
+ queue_readl(queue, ISR);
+ if (bp->caps & MACB_CAPS_ISR_CLEAR_ON_WRITE)
+ queue_writel(queue, ISR, -1);
+ }
+
+ for (q = 0, queue = bp->queues; q < bp->num_queues; ++q, ++queue) {
+ napi_disable(&queue->napi_rx);
+ napi_disable(&queue->napi_tx);
+ }
+}
+
+static void macb_context_swap_end(struct macb *bp,
+ struct macb_context *new_ctx)
+{
+ struct macb_context *old_ctx;
+ struct macb_queue *queue;
+ unsigned int q;
+ u32 ctrl;
+
+ /* Swap contexts & give buffer pointers to HW. */
+
+ old_ctx = bp->ctx;
+ bp->ctx = new_ctx;
+ macb_init_buffers(bp);
+
+ /* Start NAPI, HW Tx/Rx and software Tx. */
+
+ for (q = 0, queue = bp->queues; q < bp->num_queues; ++q, ++queue) {
+ napi_enable(&queue->napi_rx);
+ napi_enable(&queue->napi_tx);
+ }
+
+ if (!(bp->caps & MACB_CAPS_MACB_IS_EMAC)) {
+ for (q = 0, queue = bp->queues; q < bp->num_queues;
+ ++q, ++queue) {
+ queue_writel(queue, IER,
+ bp->rx_intr_mask |
+ MACB_TX_INT_FLAGS |
+ MACB_BIT(HRESP));
+ }
+ }
+
+ ctrl = macb_readl(bp, NCR);
+ macb_writel(bp, NCR, ctrl | MACB_BIT(RE) | MACB_BIT(TE));
+
+ netif_tx_start_all_queues(bp->netdev);
+
+ /* Free old context. */
+
+ macb_free_consistent(old_ctx);
+}
+
static void gem_init_rx_ring(struct macb_context *ctx, unsigned int q)
{
struct macb_rxq *rxq = &ctx->rxq[q];
@@ -3819,9 +3889,10 @@ static int macb_set_ringparam(struct net_device *netdev,
struct kernel_ethtool_ringparam *kernel_ring,
struct netlink_ext_ack *extack)
{
+ unsigned int new_rx_size, new_tx_size;
struct macb *bp = netdev_priv(netdev);
- u32 new_rx_size, new_tx_size;
- unsigned int reset = 0;
+ bool running = netif_running(netdev);
+ struct macb_context *new_ctx;

if ((ring->rx_mini_pending) || (ring->rx_jumbo_pending))
return -EINVAL;
@@ -3840,16 +3911,20 @@ static int macb_set_ringparam(struct net_device *netdev,
return 0;
}

- if (netif_running(bp->netdev)) {
- reset = 1;
- macb_close(bp->netdev);
+ if (running) {
+ new_ctx = macb_context_alloc(bp, netdev->mtu,
+ new_rx_size, new_tx_size);
+ if (IS_ERR(new_ctx))
+ return PTR_ERR(new_ctx);
+
+ macb_context_swap_start(bp);
}

bp->configured_rx_ring_size = new_rx_size;
bp->configured_tx_ring_size = new_tx_size;

- if (reset)
- macb_open(bp->netdev);
+ if (running)
+ macb_context_swap_end(bp, new_ctx);

return 0;
}

--
2.53.0