[PATCH net-next v2 05/14] net: macb: allocate tieoff descriptor once across device lifetime

Théo Lebrun
2026-04-10T19:52:19Z

The tieoff descriptor is a RX DMA descriptor ring of size one. It gets
configured onto queues for Wake-on-LAN during system-wide suspend when
hardware does not support disabling individual queues
(MACB_CAPS_QUEUE_DISABLE).

MACB/GEM driver allocates it alongside the main RX ring
inside macb_alloc_consistent() at open. Free is done by
macb_free_consistent() at close.

Change to allocate once at probe and free on probe failure or device
removal. This makes the tieoff descriptor lifetime much longer,
avoiding repeating coherent buffer allocation on each open/close cycle.

Main benefit: we dissociate its lifetime from the main ring's lifetime.
That way there is less work to be doing on resources (re)alloc. This
currently happens on close/open, but will soon also happen on context
swap operations (set_ringparam, change_mtu, set_channels, etc).

Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
---
drivers/net/ethernet/cadence/macb_main.c | 75 +++++++++++++++++---------------
1 file changed, 41 insertions(+), 34 deletions(-)

diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
index c5d8e8f835ba..ec030801ed68 100644
--- a/drivers/net/ethernet/cadence/macb_main.c
+++ b/drivers/net/ethernet/cadence/macb_main.c
@@ -2653,12 +2653,6 @@ static void macb_free_consistent(struct macb *bp)
unsigned int q;
size_t size;

- if (bp->rx_ring_tieoff) {
- dma_free_coherent(dev, macb_dma_desc_get_size(bp),
- bp->rx_ring_tieoff, bp->rx_ring_tieoff_dma);
- bp->rx_ring_tieoff = NULL;
- }
-
bp->macbgem_ops.mog_free_rx_buffers(bp);

size = bp->num_queues * macb_tx_ring_size_per_queue(bp);
@@ -2756,16 +2750,6 @@ static int macb_alloc_consistent(struct macb *bp)
if (bp->macbgem_ops.mog_alloc_rx_buffers(bp))
goto out_err;

- /* Required for tie off descriptor for PM cases */
- if (!(bp->caps & MACB_CAPS_QUEUE_DISABLE)) {
- bp->rx_ring_tieoff = dma_alloc_coherent(&bp->pdev->dev,
- macb_dma_desc_get_size(bp),
- &bp->rx_ring_tieoff_dma,
- GFP_KERNEL);
- if (!bp->rx_ring_tieoff)
- goto out_err;
- }
-
return 0;

out_err:
@@ -2773,19 +2757,6 @@ static int macb_alloc_consistent(struct macb *bp)
return -ENOMEM;
}

-static void macb_init_tieoff(struct macb *bp)
-{
- struct macb_dma_desc *desc = bp->rx_ring_tieoff;
-
- if (bp->caps & MACB_CAPS_QUEUE_DISABLE)
- return;
- /* Setup a wrapping descriptor with no free slots
- * (WRAP and USED) to tie off/disable unused RX queues.
- */
- macb_set_addr(bp, desc, MACB_BIT(RX_WRAP) | MACB_BIT(RX_USED));
- desc->ctrl = 0;
-}
-
static void gem_init_rx_ring(struct macb_queue *queue)
{
queue->rx_tail = 0;
@@ -2813,8 +2784,6 @@ static void gem_init_rings(struct macb *bp)

gem_init_rx_ring(queue);
}
-
- macb_init_tieoff(bp);
}

static void macb_init_rings(struct macb *bp)
@@ -2832,8 +2801,6 @@ static void macb_init_rings(struct macb *bp)
bp->queues[0].tx_head = 0;
bp->queues[0].tx_tail = 0;
desc->ctrl |= MACB_BIT(TX_WRAP);
-
- macb_init_tieoff(bp);
}

static void macb_reset_hw(struct macb *bp)
@@ -5510,6 +5477,38 @@ static int eyeq5_init(struct platform_device *pdev)
return ret;
}

+static int macb_alloc_tieoff(struct macb *bp)
+{
+ /* Tieoff is a workaround in case HW cannot disable queues, for PM. */
+ if (bp->caps & MACB_CAPS_QUEUE_DISABLE)
+ return 0;
+
+ bp->rx_ring_tieoff = dma_alloc_coherent(&bp->pdev->dev,
+ macb_dma_desc_get_size(bp),
+ &bp->rx_ring_tieoff_dma,
+ GFP_KERNEL);
+ if (!bp->rx_ring_tieoff)
+ return -ENOMEM;
+
+ macb_set_addr(bp, bp->rx_ring_tieoff,
+ MACB_BIT(RX_WRAP) | MACB_BIT(RX_USED));
+
+ bp->rx_ring_tieoff->ctrl = 0;
+
+ return 0;
+}
+
+static void macb_free_tieoff(struct macb *bp)
+{
+ if (!bp->rx_ring_tieoff)
+ return;
+
+ dma_free_coherent(&bp->pdev->dev, macb_dma_desc_get_size(bp),
+ bp->rx_ring_tieoff,
+ bp->rx_ring_tieoff_dma);
+ bp->rx_ring_tieoff = NULL;
+}
+
static const struct macb_usrio_config mpfs_usrio = {
.tsu_source = 0,
};
@@ -5919,10 +5918,14 @@ static int macb_probe(struct platform_device *pdev)

netif_carrier_off(netdev);

+ err = macb_alloc_tieoff(bp);
+ if (err)
+ goto err_out_unregister_mdio;
+
err = register_netdev(netdev);
if (err) {
dev_err(&pdev->dev, "Cannot register net device, aborting.\n");
- goto err_out_unregister_mdio;
+ goto err_out_free_tieoff;
}

INIT_WORK(&bp->hresp_err_bh_work, macb_hresp_error_task);
@@ -5936,6 +5939,9 @@ static int macb_probe(struct platform_device *pdev)

return 0;

+err_out_free_tieoff:
+ macb_free_tieoff(bp);
+
err_out_unregister_mdio:
mdiobus_unregister(bp->mii_bus);
mdiobus_free(bp->mii_bus);
@@ -5965,6 +5971,7 @@ static void macb_remove(struct platform_device *pdev)
if (netdev) {
bp = netdev_priv(netdev);
unregister_netdev(netdev);
+ macb_free_tieoff(bp);
phy_exit(bp->phy);
mdiobus_unregister(bp->mii_bus);
mdiobus_free(bp->mii_bus);

--
2.53.0