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

["Théo Lebrun" <theo.lebrun@bootlin.com>]

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