[net-next,3/6] gve: Add initial gve_clock

Commit Message

Harshitha Ramamurthy April 18, 2025, 10:12 p.m. UTC

From: Kevin Yang <[e-mail]>

This initial version of the gve clock only performs one major function,
managing querying the nic clock and storing the results.

The timestamp delivered in descriptors has a wraparound time of ~4
seconds so 250ms is chosen as the sync cadence to provide a balance
between performance, and drift potential when we do start associating
host time and nic time.

A dedicated ordered workqueue has been setup to ensure a consistent
cadence for querying the nic clock.

Co-developed-by: John Fraker <[e-mail]>
Signed-off-by: John Fraker <[e-mail]>
Co-developed-by: Ziwei Xiao <[e-mail]>
Signed-off-by: Ziwei Xiao <[e-mail]>
Co-developed-by: Tim Hostetler <[e-mail]>
Signed-off-by: Tim Hostetler <[e-mail]>
Reviewed-by: Willem de Bruijn <[e-mail]>
Signed-off-by: Kevin Yang <[e-mail]>
Signed-off-by: Harshitha Ramamurthy <[e-mail]>
---
 drivers/net/ethernet/google/gve/Makefile    |   2 +-
 drivers/net/ethernet/google/gve/gve.h       |   8 ++
 drivers/net/ethernet/google/gve/gve_clock.c | 103 ++++++++++++++++++++
 3 files changed, 112 insertions(+), 1 deletion(-)
 create mode 100644 drivers/net/ethernet/google/gve/gve_clock.c

Patch

diff --git a/drivers/net/ethernet/google/gve/Makefile b/drivers/net/ethernet/google/gve/Makefile
index 4520f1c07a63..c8fae2c03f2b 100644
--- a/drivers/net/ethernet/google/gve/Makefile
+++ b/drivers/net/ethernet/google/gve/Makefile
@@ -2,4 +2,4 @@ 
 
 obj-$(CONFIG_GVE) += gve.o
 gve-objs := gve_main.o gve_tx.o gve_tx_dqo.o gve_rx.o gve_rx_dqo.o gve_ethtool.o gve_adminq.o gve_utils.o gve_flow_rule.o \
-	    gve_buffer_mgmt_dqo.o
+	    gve_buffer_mgmt_dqo.o gve_clock.o
diff --git a/drivers/net/ethernet/google/gve/gve.h b/drivers/net/ethernet/google/gve/gve.h
index cf6947731a9b..5a141a8735d6 100644
--- a/drivers/net/ethernet/google/gve/gve.h
+++ b/drivers/net/ethernet/google/gve/gve.h
@@ -873,7 +873,12 @@  struct gve_priv {
 	struct gve_rss_config rss_config;
 
 	/* True if the device supports reading the nic clock */
+	struct workqueue_struct *gve_ts_wq;
 	bool nic_timestamp_supported;
+	struct delayed_work nic_ts_sync_task;
+	struct gve_nic_ts_report *nic_ts_report;
+	dma_addr_t nic_ts_report_bus;
+	u64 last_sync_nic_counter; /* Clock counter from last NIC TS report */
 };
 
 enum gve_service_task_flags_bit {
@@ -1255,6 +1260,9 @@  int gve_flow_rules_reset(struct gve_priv *priv);
 int gve_init_rss_config(struct gve_priv *priv, u16 num_queues);
 /* report stats handling */
 void gve_handle_report_stats(struct gve_priv *priv);
+/* Timestamping */
+int gve_init_clock(struct gve_priv *priv);
+void gve_teardown_clock(struct gve_priv *priv);
 /* exported by ethtool.c */
 extern const struct ethtool_ops gve_ethtool_ops;
 /* needed by ethtool */
diff --git a/drivers/net/ethernet/google/gve/gve_clock.c b/drivers/net/ethernet/google/gve/gve_clock.c
new file mode 100644
index 000000000000..464ce9a6f4b6
--- /dev/null
+++ b/drivers/net/ethernet/google/gve/gve_clock.c
@@ -0,0 +1,103 @@ 
+// SPDX-License-Identifier: (GPL-2.0 OR MIT)
+/* Google virtual Ethernet (gve) driver
+ *
+ * Copyright (C) 2015-2025 Google LLC
+ */
+
+#include "gve.h"
+#include "gve_adminq.h"
+
+/* Interval to schedule a nic timestamp calibration, 250ms. */
+#define GVE_NIC_TS_SYNC_INTERVAL_MS 250
+
+/* Read the nic timestamp from hardware via the admin queue. */
+static int gve_clock_nic_ts_read(struct gve_priv *priv)
+{
+	u64 nic_raw;
+	int err;
+
+	err = gve_adminq_report_nic_ts(priv, priv->nic_ts_report_bus);
+	if (err)
+		return err;
+
+	nic_raw = be64_to_cpu(priv->nic_ts_report->nic_timestamp);
+	WRITE_ONCE(priv->last_sync_nic_counter, nic_raw);
+
+	return 0;
+}
+
+static void gve_nic_ts_sync_task(struct work_struct *work)
+{
+	struct gve_priv *priv = container_of(work, struct gve_priv,
+					     nic_ts_sync_task.work);
+	int err;
+
+	if (gve_get_reset_in_progress(priv) || !gve_get_admin_queue_ok(priv))
+		goto out;
+
+	err = gve_clock_nic_ts_read(priv);
+	if (err && net_ratelimit())
+		dev_err(&priv->pdev->dev,
+			"%s read err %d\n", __func__, err);
+
+out:
+	queue_delayed_work(priv->gve_wq, &priv->nic_ts_sync_task,
+			   msecs_to_jiffies(GVE_NIC_TS_SYNC_INTERVAL_MS));
+}
+
+int gve_init_clock(struct gve_priv *priv)
+{
+	int err;
+
+	if (!priv->nic_timestamp_supported)
+		return -EPERM;
+
+	priv->nic_ts_report =
+		dma_alloc_coherent(&priv->pdev->dev,
+				   sizeof(struct gve_nic_ts_report),
+				   &priv->nic_ts_report_bus,
+				   GFP_KERNEL);
+	if (!priv->nic_ts_report) {
+		dev_err(&priv->pdev->dev, "%s dma alloc error\n", __func__);
+		return -ENOMEM;
+	}
+
+	err = gve_clock_nic_ts_read(priv);
+	if (err) {
+		dev_err(&priv->pdev->dev, "%s read error %d\n", __func__, err);
+		goto free_nic_ts_report;
+	}
+
+	priv->gve_ts_wq = alloc_ordered_workqueue("gve-ts", 0);
+	if (!priv->gve_ts_wq) {
+		dev_err(&priv->pdev->dev, "%s Could not allocate workqueue\n",
+			__func__);
+		err = -ENOMEM;
+		goto free_nic_ts_report;
+	}
+	INIT_DELAYED_WORK(&priv->nic_ts_sync_task, gve_nic_ts_sync_task);
+	queue_delayed_work(priv->gve_ts_wq, &priv->nic_ts_sync_task,
+			   msecs_to_jiffies(GVE_NIC_TS_SYNC_INTERVAL_MS));
+
+	return 0;
+
+free_nic_ts_report:
+	dma_free_coherent(&priv->pdev->dev,
+			  sizeof(struct gve_nic_ts_report),
+			  priv->nic_ts_report, priv->nic_ts_report_bus);
+	priv->nic_ts_report = NULL;
+
+	return err;
+}
+
+void gve_teardown_clock(struct gve_priv *priv)
+{
+	if (priv->nic_ts_report) {
+		cancel_delayed_work_sync(&priv->nic_ts_sync_task);
+		destroy_workqueue(priv->gve_ts_wq);
+		dma_free_coherent(&priv->pdev->dev,
+				  sizeof(struct gve_nic_ts_report),
+				  priv->nic_ts_report, priv->nic_ts_report_bus);
+		priv->nic_ts_report = NULL;
+	}
+}