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Thu, 19 Mar 2026 16:33:36 +0000 Received: from airavat.amd.com (10.180.168.240) by satlexmb07.amd.com (10.181.42.216) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.17; Thu, 19 Mar 2026 11:33:33 -0500 From: Raju Rangoju To: CC: , , , , , , "Raju Rangoju" Subject: [PATCH v3 net-next 3/3] amd-xgbe: add TX descriptor cleanup for link-down Date: Thu, 19 Mar 2026 22:02:51 +0530 Message-ID: <20260319163251.1808611-4-Raju.Rangoju@amd.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260319163251.1808611-1-Raju.Rangoju@amd.com> References: <20260319163251.1808611-1-Raju.Rangoju@amd.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: satlexmb07.amd.com (10.181.42.216) To satlexmb07.amd.com (10.181.42.216) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS2PEPF000061C6:EE_|SA1PR12MB9469:EE_ X-MS-Office365-Filtering-Correlation-Id: 4a1447bb-e6a7-4d6e-fd74-08de85d544bc X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|36860700016|82310400026|1800799024|22082099003|18002099003|56012099003; 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When the link goes down while TX packets are in-flight, the hardware stops processing descriptors with the OWN bit still set. The current driver waits indefinitely for these descriptors to complete, which never happens. This causes: - TX ring exhaustion (no descriptors available for new packets) - Memory leaks (skbs never freed) - DMA mapping leaks (mappings never unmapped) - Network stack backpressure buildup Add force-cleanup mechanism in xgbe_tx_poll() that detects link-down state and reclaims abandoned descriptors. The helper functions and DMA optimizations support efficient TX shutdown: - xgbe_wait_for_dma_tx_complete(): Wait for DMA completion with link-down optimization - Restructure xgbe_disable_tx() for proper shutdown sequence Implementation: 1. Check link state at the start of tx_poll 2. If link is down, set force_cleanup flag 3. For descriptors that hardware hasn't completed (!tx_complete): - If force_cleanup: treat as completed and reclaim resources - If link up: break and wait for hardware (normal behavior) The cleanup process: - Frees skbs that will never be transmitted - Unmaps DMA mappings - Resets descriptors for reuse - Does NOT count as successful transmission (correct statistics) Benefits: - Prevents TX ring starvation - Eliminates memory and DMA mapping leaks - Enables fast link recovery when link comes back up - Critical for link aggregation failover scenarios Signed-off-by: Raju Rangoju --- Changes since v2: - remove the stale function xgbe_reset_tx_queues(), otherwise it would result in undefined symbol during linking. drivers/net/ethernet/amd/xgbe/xgbe-common.h | 4 ++ drivers/net/ethernet/amd/xgbe/xgbe-dev.c | 77 ++++++++++++++++++--- drivers/net/ethernet/amd/xgbe/xgbe-drv.c | 43 ++++++++++-- 3 files changed, 108 insertions(+), 16 deletions(-) diff --git a/drivers/net/ethernet/amd/xgbe/xgbe-common.h b/drivers/net/ethernet/amd/xgbe/xgbe-common.h index c17900a49595..66807d67e984 100644 --- a/drivers/net/ethernet/amd/xgbe/xgbe-common.h +++ b/drivers/net/ethernet/amd/xgbe/xgbe-common.h @@ -330,6 +330,10 @@ #define MAC_ISR_SMI_WIDTH 1 #define MAC_ISR_TSIS_INDEX 12 #define MAC_ISR_TSIS_WIDTH 1 +#define MAC_ISR_LS_INDEX 24 +#define MAC_ISR_LS_WIDTH 2 +#define MAC_ISR_LSI_INDEX 0 +#define MAC_ISR_LSI_WIDTH 1 #define MAC_MACA1HR_AE_INDEX 31 #define MAC_MACA1HR_AE_WIDTH 1 #define MAC_MDIOIER_SNGLCOMPIE_INDEX 12 diff --git a/drivers/net/ethernet/amd/xgbe/xgbe-dev.c b/drivers/net/ethernet/amd/xgbe/xgbe-dev.c index b7bf74c6bb47..2de974213090 100644 --- a/drivers/net/ethernet/amd/xgbe/xgbe-dev.c +++ b/drivers/net/ethernet/amd/xgbe/xgbe-dev.c @@ -3276,28 +3276,83 @@ static void xgbe_enable_tx(struct xgbe_prv_data *pdata) XGMAC_IOWRITE_BITS(pdata, MAC_TCR, TE, 1); } -static void xgbe_disable_tx(struct xgbe_prv_data *pdata) +/** + * xgbe_wait_for_dma_tx_complete - Wait for DMA to complete pending TX + * @pdata: driver private data + * + * Wait for the DMA TX channels to complete all pending descriptors. + * This ensures no frames are in-flight before we disable the transmitter. + * If link is down, return immediately as TX will never complete. + * + * Return: 0 on success, -ETIMEDOUT on timeout + */ +static int xgbe_wait_for_dma_tx_complete(struct xgbe_prv_data *pdata) { + struct xgbe_channel *channel; + struct xgbe_ring *ring; + unsigned long timeout; unsigned int i; + bool complete; - /* Prepare for Tx DMA channel stop */ - for (i = 0; i < pdata->tx_q_count; i++) - xgbe_prepare_tx_stop(pdata, i); + /* If link is down, TX will never complete - skip waiting */ + if (!pdata->phy.link) + return 0; - /* Disable MAC Tx */ - XGMAC_IOWRITE_BITS(pdata, MAC_TCR, TE, 0); + timeout = jiffies + (XGBE_DMA_STOP_TIMEOUT * HZ); - /* Disable each Tx queue */ - for (i = 0; i < pdata->tx_q_count; i++) - XGMAC_MTL_IOWRITE_BITS(pdata, i, MTL_Q_TQOMR, TXQEN, 0); + do { + complete = true; - /* Disable each Tx DMA channel */ + for (i = 0; i < pdata->channel_count; i++) { + channel = pdata->channel[i]; + ring = channel->tx_ring; + if (!ring) + continue; + + /* Check if DMA has processed all descriptors */ + if (ring->dirty != ring->cur) { + complete = false; + break; + } + } + + if (complete) + return 0; + + usleep_range(100, 200); + } while (time_before(jiffies, timeout)); + + netif_warn(pdata, drv, pdata->netdev, + "timeout waiting for DMA TX to complete\n"); + return -ETIMEDOUT; +} + +static void xgbe_disable_tx(struct xgbe_prv_data *pdata) +{ + unsigned int i; + + /* Step 1: Wait for DMA to complete pending descriptors */ + xgbe_wait_for_dma_tx_complete(pdata); + + /* Step 2: Disable each Tx DMA channel to stop + * processing new descriptors + */ for (i = 0; i < pdata->channel_count; i++) { if (!pdata->channel[i]->tx_ring) break; - XGMAC_DMA_IOWRITE_BITS(pdata->channel[i], DMA_CH_TCR, ST, 0); } + + /* Step 3: Wait for MTL TX queues to drain */ + for (i = 0; i < pdata->tx_q_count; i++) + xgbe_prepare_tx_stop(pdata, i); + + /* Step 4: Disable MTL TX queues */ + for (i = 0; i < pdata->tx_q_count; i++) + XGMAC_MTL_IOWRITE_BITS(pdata, i, MTL_Q_TQOMR, TXQEN, 0); + + /* Step 5: Disable MAC TX last */ + XGMAC_IOWRITE_BITS(pdata, MAC_TCR, TE, 0); } static void xgbe_prepare_rx_stop(struct xgbe_prv_data *pdata, diff --git a/drivers/net/ethernet/amd/xgbe/xgbe-drv.c b/drivers/net/ethernet/amd/xgbe/xgbe-drv.c index 6886d3b33ffe..2d6d00e3689b 100644 --- a/drivers/net/ethernet/amd/xgbe/xgbe-drv.c +++ b/drivers/net/ethernet/amd/xgbe/xgbe-drv.c @@ -2169,6 +2169,7 @@ static int xgbe_tx_poll(struct xgbe_channel *channel) struct net_device *netdev = pdata->netdev; struct netdev_queue *txq; int processed = 0; + int force_cleanup; unsigned int tx_packets = 0, tx_bytes = 0; unsigned int cur; @@ -2185,13 +2186,41 @@ static int xgbe_tx_poll(struct xgbe_channel *channel) txq = netdev_get_tx_queue(netdev, channel->queue_index); + /* Smart descriptor cleanup during link-down conditions. + * + * When link is down, hardware stops processing TX descriptors (OWN bit + * remains set). Enable intelligent cleanup to reclaim these abandoned + * descriptors and maintain TX queue health. + * + * This cleanup mechanism enables: + * - Continuous TX queue availability for new packets when link recovers + * - Clean resource management (skbs, DMA mappings, descriptors) + * - Fast failover in link aggregation scenarios + */ + force_cleanup = !pdata->phy.link; + while ((processed < XGBE_TX_DESC_MAX_PROC) && (ring->dirty != cur)) { rdata = XGBE_GET_DESC_DATA(ring, ring->dirty); rdesc = rdata->rdesc; - if (!hw_if->tx_complete(rdesc)) - break; + if (!hw_if->tx_complete(rdesc)) { + if (!force_cleanup) + break; + /* Link-down descriptor cleanup: reclaim abandoned + * resources. + * + * Hardware has stopped processing this descriptor, so + * perform intelligent cleanup to free skbs and reclaim + * descriptors for future use when link recovers. + * + * These are not counted as successful transmissions + * since packets never reached the wire. + */ + netif_dbg(pdata, tx_err, netdev, + "force-freeing stuck TX desc %u (link down)\n", + ring->dirty); + } /* Make sure descriptor fields are read after reading the OWN * bit */ @@ -2200,9 +2229,13 @@ static int xgbe_tx_poll(struct xgbe_channel *channel) if (netif_msg_tx_done(pdata)) xgbe_dump_tx_desc(pdata, ring, ring->dirty, 1, 0); - if (hw_if->is_last_desc(rdesc)) { - tx_packets += rdata->tx.packets; - tx_bytes += rdata->tx.bytes; + /* Only count packets actually transmitted (not force-cleaned) + */ + if (!force_cleanup || hw_if->is_last_desc(rdesc)) { + if (hw_if->is_last_desc(rdesc)) { + tx_packets += rdata->tx.packets; + tx_bytes += rdata->tx.bytes; + } } /* Free the SKB and reset the descriptor for re-use */ -- 2.34.1