[PATCH v4] net: mvneta_bm: add suspend/resume support to prevent crash after resume

[Yun Zhou <yun.zhou@windriver.com>]

The mvneta driver uses the hardware Buffer Manager (BM) for RX buffer
allocation. During suspend, mvneta disables its clock, causing BM to
lose all buffer address state. On resume, mvneta_bm_port_init() re-
attaches the BM pool to the NIC, but BM hardware returns stale/garbage
buffer addresses. When NAPI poll processes these buffers, DMA cache
sync hits an invalid virtual address causing a kernel panic:

 Unable to handle kernel paging request at virtual address b0000080
 PC is at v7_dma_inv_range
 Call trace:
  v7_dma_inv_range from arch_sync_dma_for_cpu+0x94/0x158
  arch_sync_dma_for_cpu from __dma_sync_single_for_cpu+0xc4/0x15c
  __dma_sync_single_for_cpu from mvneta_rx_swbm+0x6c8/0xf48
  mvneta_rx_swbm from mvneta_poll+0x6fc/0x70c
  mvneta_poll from __napi_poll.constprop.0+0x2c/0x1e0
  __napi_poll.constprop.0 from net_rx_action+0x160/0x2c4
  net_rx_action from handle_softirqs+0xd8/0x2b8
  handle_softirqs from run_ksoftirqd+0x30/0x94
  run_ksoftirqd from smpboot_thread_fn+0x100/0x204
  smpboot_thread_fn from kthread+0xf4/0x110
  kthread from ret_from_fork+0x14/0x28

Fix by adding suspend/resume callbacks to the BM driver:

- suspend: drain all buffers (with DMA unmapping), free the BPPE
  regions, and reset pool state to FREE before stopping BM and gating
  the clock.

- resume: enable the clock, reinitialize BM defaults, and restore pool
  read/write pointers and size registers. Pool allocation and buffer
  refill are handled by mvneta_resume() through the normal
  mvneta_bm_port_init() path, which sees pools as FREE and performs
  full initialization identical to probe.

Add a device_link (DL_FLAG_AUTOREMOVE_CONSUMER) in mvneta_probe to
guarantee BM resumes before mvneta and suspends after mvneta. If the
link cannot be created, fall back to SW buffer management to avoid a
potential crash on resume due to unordered PM transitions.

Signed-off-by: Yun Zhou <yun.zhou@windriver.com>
---
v4:
  - On device_link_add() failure, fall back to SW buffer management
    (destroy pools, put BM reference, clear bm_priv) instead of merely
    emitting a warning. Without the link, suspend/resume ordering is
    not guaranteed and the original crash can still occur.

v3:
  - Restore per-pool POOL_SIZE_REG, POOL_READ_PTR_REG, and
    POOL_WRITE_PTR_REG in resume, since clock gating loses all BM
    register state.
  - Check device_link_add() return value and emit dev_warn on failure.
  - Replace SIMPLE_DEV_PM_OPS (deprecated) with
    DEFINE_SIMPLE_DEV_PM_OPS and pm_sleep_ptr(), removing the
    #ifdef CONFIG_PM_SLEEP guard.
  - Add dev_warn in suspend if not all buffers could be freed.

v2:
  - Drain buffers via mvneta_bm_bufs_free() in suspend instead of only
    stopping BM and gating the clock. This ensures proper DMA unmapping
    and avoids buffer leaks.
  - Free the BPPE DMA-coherent region in suspend so that resume takes
    the full probe-time initialization path (alloc + fill), eliminating
    the need to modify mvneta_bm_pool_create().
  - Reset pool type to MVNETA_BM_FREE in suspend so mvneta_bm_pool_use()
    correctly re-creates and refills pools on resume.
  - Check clk_prepare_enable() return value in resume.
  - Add device_link between mvneta (consumer) and mvneta_bm (supplier)
    to guarantee correct suspend/resume ordering.

 drivers/net/ethernet/marvell/mvneta.c    | 18 ++++++++
 drivers/net/ethernet/marvell/mvneta_bm.c | 58 ++++++++++++++++++++++++
 2 files changed, 76 insertions(+)

diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
index 744d6585a949..543e566425c1 100644
--- a/drivers/net/ethernet/marvell/mvneta.c
+++ b/drivers/net/ethernet/marvell/mvneta.c
@@ -5678,6 +5678,24 @@ static int mvneta_probe(struct platform_device *pdev)
 					 "use SW buffer management\n");
 				mvneta_bm_put(pp->bm_priv);
 				pp->bm_priv = NULL;
+			} else if (!device_link_add(&pdev->dev,
+						    &pp->bm_priv->pdev->dev,
+						    DL_FLAG_AUTOREMOVE_CONSUMER)) {
+				/*
+				 * Link guarantees BM resumes before mvneta.
+				 * Without it, BM may not be ready when
+				 * mvneta_bm_port_init() runs on resume,
+				 * causing stale buffer addresses and a crash.
+				 * Fall back to SW management to be safe.
+				 */
+				dev_warn(&pdev->dev,
+					 "failed to link to BM, use SW buffer management\n");
+				mvneta_bm_pool_destroy(pp->bm_priv,
+						       pp->pool_long, 1 << pp->id);
+				mvneta_bm_pool_destroy(pp->bm_priv,
+						       pp->pool_short, 1 << pp->id);
+				mvneta_bm_put(pp->bm_priv);
+				pp->bm_priv = NULL;
 			}
 		}
 		/* Set RX packet offset correction for platforms, whose
diff --git a/drivers/net/ethernet/marvell/mvneta_bm.c b/drivers/net/ethernet/marvell/mvneta_bm.c
index 6bb380494919..85162a43eaf6 100644
--- a/drivers/net/ethernet/marvell/mvneta_bm.c
+++ b/drivers/net/ethernet/marvell/mvneta_bm.c
@@ -477,6 +477,63 @@ static void mvneta_bm_remove(struct platform_device *pdev)
 	clk_disable_unprepare(priv->clk);
 }
 
+static int mvneta_bm_suspend(struct device *dev)
+{
+	struct mvneta_bm *priv = dev_get_drvdata(dev);
+	int i;
+
+	/* Drain buffers and free pool resources while BM is still clocked */
+	for (i = 0; i < MVNETA_BM_POOLS_NUM; i++) {
+		struct mvneta_bm_pool *bm_pool = &priv->bm_pools[i];
+		int size_bytes;
+
+		if (bm_pool->type == MVNETA_BM_FREE)
+			continue;
+
+		mvneta_bm_bufs_free(priv, bm_pool, bm_pool->port_map);
+		if (bm_pool->hwbm_pool.buf_num)
+			dev_warn(&priv->pdev->dev,
+				 "pool %d: %d buffers not freed\n",
+				 bm_pool->id, bm_pool->hwbm_pool.buf_num);
+
+		size_bytes = sizeof(u32) * bm_pool->hwbm_pool.size;
+		dma_free_coherent(&priv->pdev->dev, size_bytes,
+				  bm_pool->virt_addr, bm_pool->phys_addr);
+		bm_pool->virt_addr = NULL;
+		bm_pool->type = MVNETA_BM_FREE;
+	}
+
+	mvneta_bm_write(priv, MVNETA_BM_COMMAND_REG, MVNETA_BM_STOP_MASK);
+	clk_disable_unprepare(priv->clk);
+	return 0;
+}
+
+static int mvneta_bm_resume(struct device *dev)
+{
+	struct mvneta_bm *priv = dev_get_drvdata(dev);
+	int i, err;
+
+	err = clk_prepare_enable(priv->clk);
+	if (err)
+		return err;
+
+	/* Reinitialize BM hardware; pools are refilled by mvneta_resume() */
+	mvneta_bm_default_set(priv);
+
+	/* Restore pool registers lost during clock gating */
+	for (i = 0; i < MVNETA_BM_POOLS_NUM; i++) {
+		mvneta_bm_write(priv, MVNETA_BM_POOL_READ_PTR_REG(i), 0);
+		mvneta_bm_write(priv, MVNETA_BM_POOL_WRITE_PTR_REG(i), 0);
+		mvneta_bm_write(priv, MVNETA_BM_POOL_SIZE_REG(i),
+				priv->bm_pools[i].hwbm_pool.size);
+	}
+
+	mvneta_bm_write(priv, MVNETA_BM_COMMAND_REG, MVNETA_BM_START_MASK);
+	return 0;
+}
+
+static DEFINE_SIMPLE_DEV_PM_OPS(mvneta_bm_pm_ops, mvneta_bm_suspend, mvneta_bm_resume);
+
 static const struct of_device_id mvneta_bm_match[] = {
 	{ .compatible = "marvell,armada-380-neta-bm" },
 	{ }
@@ -489,6 +546,7 @@ static struct platform_driver mvneta_bm_driver = {
 	.driver = {
 		.name = MVNETA_BM_DRIVER_NAME,
 		.of_match_table = mvneta_bm_match,
+		.pm = pm_sleep_ptr(&mvneta_bm_pm_ops),
 	},
 };
 
-- 
2.43.0