Quanyang observed that when using an NFS rootfs on an AMD ZynqMp board, the rootfs may take an extended time to recover after a suspend. Upon investigation, it was determined that the issue originates from a problem in the macb driver. According to the Zynq UltraScale TRM [1], when transmit is disabled, the transmit buffer queue pointer resets to point to the address specified by the transmit buffer queue base address register. In the current implementation, the code merely resets `queue->tx_head` and `queue->tx_tail` to '0'. This approach presents several issues: - Packets already queued in the tx ring are silently lost, leading to memory leaks since the associated skbs cannot be released. - Concurrent write access to `queue->tx_head` and `queue->tx_tail` may occur from `macb_tx_poll()` or `macb_start_xmit()` when these values are reset to '0'. - The transmission may become stuck on a packet that has already been sent out, with its 'TX_USED' bit set, but has not yet been processed. However, due to the manipulation of 'queue->tx_head' and 'queue->tx_tail', `macb_tx_poll()` incorrectly assumes there are no packets to handle because `queue->tx_head == queue->tx_tail`. This issue is only resolved when a new packet is placed at this position. This is the root cause of the prolonged recovery time observed for the NFS root filesystem. To resolve this issue, shuffle the tx ring and tx skb array so that the first unsent packet is positioned at the start of the tx ring. Additionally, ensure that updates to `queue->tx_head` and `queue->tx_tail` are properly protected with the appropriate lock. [1] https://docs.amd.com/v/u/en-US/ug1085-zynq-ultrascale-trm Fixes: bf9cf80cab81 ("net: macb: Fix tx/rx malfunction after phy link down and up") Reported-by: Quanyang Wang Signed-off-by: Kevin Hao Cc: stable@vger.kernel.org --- Cc: Nicolas Ferre Cc: Claudiu Beznea Cc: Andrew Lunn Cc: "David S. Miller" Cc: Eric Dumazet Cc: Jakub Kicinski Cc: Paolo Abeni Cc: Russell King --- drivers/net/ethernet/cadence/macb_main.c | 89 ++++++++++++++++++++++++++++++-- 1 file changed, 86 insertions(+), 3 deletions(-) diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c index 17f0ad3d7a0924a7dc2fc0a13505aff7d2499ffa..fce144a1830823da9821ad3245784e62fed97e33 100644 --- a/drivers/net/ethernet/cadence/macb_main.c +++ b/drivers/net/ethernet/cadence/macb_main.c @@ -36,6 +36,7 @@ #include #include #include +#include #include #include "macb.h" @@ -684,6 +685,88 @@ static void macb_mac_link_down(struct phylink_config *config, unsigned int mode, netif_tx_stop_all_queues(ndev); } +/* Use juggling algorithm to left rotate tx ring and tx skb array */ +static void gem_shuffle_tx_one_ring(struct macb_queue *queue) +{ + unsigned int i, head, tail, count, size, cycles, shift, curr, next; + struct macb_dma_desc desc, *desc_curr, *desc_next; + struct macb_tx_skb tx_skb, *skb_curr, *skb_next; + struct macb *bp = queue->bp; + unsigned long flags; + + spin_lock_irqsave(&queue->tx_ptr_lock, flags); + head = queue->tx_head; + tail = queue->tx_tail; + size = bp->tx_ring_size; + count = CIRC_CNT(head, tail, size); + + if (!(tail % size)) + goto unlock; + + if (!count) { + queue->tx_head = 0; + queue->tx_tail = 0; + goto unlock; + } + + shift = tail % size; + cycles = gcd(size, shift); + + for (i = 0; i < cycles; i++) { + memcpy(&desc, macb_tx_desc(queue, i), sizeof(struct macb_dma_desc)); + memcpy(&tx_skb, macb_tx_skb(queue, i), sizeof(struct macb_tx_skb)); + + curr = i; + next = (curr + shift) % size; + + while (next != i) { + desc_curr = macb_tx_desc(queue, curr); + desc_next = macb_tx_desc(queue, next); + + memcpy(desc_curr, desc_next, sizeof(struct macb_dma_desc)); + + if (next == bp->tx_ring_size - 1) + desc_curr->ctrl &= ~MACB_BIT(TX_WRAP); + if (curr == bp->tx_ring_size - 1) + desc_curr->ctrl |= MACB_BIT(TX_WRAP); + + skb_curr = macb_tx_skb(queue, curr); + skb_next = macb_tx_skb(queue, next); + memcpy(skb_curr, skb_next, sizeof(struct macb_tx_skb)); + + curr = next; + next = (curr + shift) % size; + } + + desc_curr = macb_tx_desc(queue, curr); + memcpy(desc_curr, &desc, sizeof(struct macb_dma_desc)); + if (i == bp->tx_ring_size - 1) + desc_curr->ctrl &= ~MACB_BIT(TX_WRAP); + if (curr == bp->tx_ring_size - 1) + desc_curr->ctrl |= MACB_BIT(TX_WRAP); + memcpy(macb_tx_skb(queue, curr), &tx_skb, sizeof(struct macb_tx_skb)); + } + + queue->tx_head = count; + queue->tx_tail = 0; + + /* Make descriptor updates visible to hardware */ + wmb(); + +unlock: + spin_unlock_irqrestore(&queue->tx_ptr_lock, flags); +} + +/* Rotate the queue so that the tail is at index 0 */ +static void gem_shuffle_tx_rings(struct macb *bp) +{ + struct macb_queue *queue; + int q; + + for (q = 0, queue = bp->queues; q < bp->num_queues; q++, queue++) + gem_shuffle_tx_one_ring(queue); +} + static void macb_mac_link_up(struct phylink_config *config, struct phy_device *phy, unsigned int mode, phy_interface_t interface, @@ -722,8 +805,6 @@ static void macb_mac_link_up(struct phylink_config *config, ctrl |= MACB_BIT(PAE); for (q = 0, queue = bp->queues; q < bp->num_queues; ++q, ++queue) { - queue->tx_head = 0; - queue->tx_tail = 0; queue_writel(queue, IER, bp->rx_intr_mask | MACB_TX_INT_FLAGS | MACB_BIT(HRESP)); } @@ -737,8 +818,10 @@ static void macb_mac_link_up(struct phylink_config *config, spin_unlock_irqrestore(&bp->lock, flags); - if (!(bp->caps & MACB_CAPS_MACB_IS_EMAC)) + if (!(bp->caps & MACB_CAPS_MACB_IS_EMAC)) { macb_set_tx_clk(bp, speed); + gem_shuffle_tx_rings(bp); + } /* Enable Rx and Tx; Enable PTP unicast */ ctrl = macb_readl(bp, NCR); --- base-commit: fc7b1a72c6cd5cbbd989c6c32a6486e3e4e3594d change-id: 20260214-zynqmp-74d35f3862f8 Best regards, -- Kevin Hao