[dpdk-dev] [PATCH v4 1/3] rte_ethdev: Add API function to read dev clock

[Tom Barbette <barbette@kth.se>]

Add rte_eth_read_clock to read the raw clock of a device.

The main use is to get the device clock conversion co-efficients to be
able to translate the raw clock of the timestamp field of the pkt mbuf
to a local synced time value.

This function was missing to allow users to convert the Rx timestamp field
to real time without the complexity of the rte_timesync* facility. One can
derivate the clock frequency by calling twice read_clock and then keep a
common time base.

Signed-off-by: Tom Barbette <barbette@kth.se>
---
 doc/guides/nics/features.rst             |  1 +
 lib/librte_ethdev/rte_ethdev.c           | 12 ++++++
 lib/librte_ethdev/rte_ethdev.h           | 47 ++++++++++++++++++++++++
 lib/librte_ethdev/rte_ethdev_core.h      |  6 +++
 lib/librte_ethdev/rte_ethdev_version.map |  1 +
 lib/librte_mbuf/rte_mbuf.h               |  2 +
 6 files changed, 69 insertions(+)

diff --git a/doc/guides/nics/features.rst b/doc/guides/nics/features.rst
index c5bf32222..025b7f812 100644
--- a/doc/guides/nics/features.rst
+++ b/doc/guides/nics/features.rst
@@ -602,6 +602,7 @@ Supports Timestamp.
 * **[provides] mbuf**: ``mbuf.ol_flags:PKT_RX_TIMESTAMP``.
 * **[provides] mbuf**: ``mbuf.timestamp``.
 * **[provides] rte_eth_dev_info**: ``rx_offload_capa,rx_queue_offload_capa: DEV_RX_OFFLOAD_TIMESTAMP``.
+* **[related] eth_dev_ops**: ``read_clock``.
 
 .. _nic_features_macsec_offload:
 
diff --git a/lib/librte_ethdev/rte_ethdev.c b/lib/librte_ethdev/rte_ethdev.c
index d7cfa3d53..9507a985f 100644
--- a/lib/librte_ethdev/rte_ethdev.c
+++ b/lib/librte_ethdev/rte_ethdev.c
@@ -4170,6 +4170,18 @@ rte_eth_timesync_write_time(uint16_t port_id, const struct timespec *timestamp)
 								timestamp));
 }
 
+int
+rte_eth_read_clock(uint16_t port_id, uint64_t *clock)
+{
+	struct rte_eth_dev *dev;
+
+	RTE_ETH_VALID_PORTID_OR_ERR_RET(port_id, -ENODEV);
+	dev = &rte_eth_devices[port_id];
+
+	RTE_FUNC_PTR_OR_ERR_RET(*dev->dev_ops->read_clock, -ENOTSUP);
+	return eth_err(port_id, (*dev->dev_ops->read_clock)(dev, clock));
+}
+
 int
 rte_eth_dev_get_reg_info(uint16_t port_id, struct rte_dev_reg_info *info)
 {
diff --git a/lib/librte_ethdev/rte_ethdev.h b/lib/librte_ethdev/rte_ethdev.h
index b8d19c69f..7dd1f8ae7 100644
--- a/lib/librte_ethdev/rte_ethdev.h
+++ b/lib/librte_ethdev/rte_ethdev.h
@@ -3793,6 +3793,53 @@ int rte_eth_timesync_read_time(uint16_t port_id, struct timespec *time);
  */
 int rte_eth_timesync_write_time(uint16_t port_id, const struct timespec *time);
 
+/**
+ * @warning
+ * @b EXPERIMENTAL: this API may change without prior notice.
+ *
+ * Read the current clock counter of an Ethernet device
+ *
+ * This returns the current raw clock value of an Ethernet device. It is
+ * a raw amount of ticks, with no given time reference.
+ * The value returned here is from the same clock than the one
+ * filling timestamp field of Rx packets when using hardware timestamp
+ * offload. Therefore it can be used to compute a precise conversion of
+ * the device clock to the real time.
+ *
+ * E.g, a simple heuristic to derivate the frequency would be:
+ * uint64_t start, end;
+ * rte_eth_read_clock(port, start);
+ * rte_delay_ms(100);
+ * rte_eth_read_clock(port, end);
+ * double freq = (end - start) * 10;
+ *
+ * Compute a common reference with:
+ * uint64_t base_time_sec = current_time();
+ * uint64_t base_clock;
+ * rte_eth_read_clock(port, base_clock);
+ *
+ * Then, convert the raw mbuf timestamp with:
+ * base_time_sec + (double)(mbuf->timestamp - base_clock) / freq;
+ *
+ * This simple example will not provide a very good accuracy. One must
+ * at least measure multiple times the frequency and do a regression.
+ * To avoid deviation from the system time, the common reference can
+ * be repeated from time to time. The integer division can also be
+ * converted by a multiplication and a shift for better performance.
+ *
+ * @param port_id
+ *   The port identifier of the Ethernet device.
+ * @param time
+ *   Pointer to the uint64_t that holds the raw clock value.
+ *
+ * @return
+ *   - 0: Success.
+ *   - -ENODEV: The port ID is invalid.
+ *   - -ENOTSUP: The function is not supported by the Ethernet driver.
+ */
+int __rte_experimental
+rte_eth_read_clock(uint16_t port_id, uint64_t *clock);
+
 /**
  * Config l2 tunnel ether type of an Ethernet device for filtering specific
  * tunnel packets by ether type.
diff --git a/lib/librte_ethdev/rte_ethdev_core.h b/lib/librte_ethdev/rte_ethdev_core.h
index 8f03f83f6..86806b3eb 100644
--- a/lib/librte_ethdev/rte_ethdev_core.h
+++ b/lib/librte_ethdev/rte_ethdev_core.h
@@ -322,6 +322,10 @@ typedef int (*eth_timesync_write_time)(struct rte_eth_dev *dev,
 				       const struct timespec *timestamp);
 /**< @internal Function used to get time from the device clock */
 
+typedef int (*eth_read_clock)(struct rte_eth_dev *dev,
+				      uint64_t *timestamp);
+/**< @internal Function used to get the current value of the device clock. */
+
 typedef int (*eth_get_reg_t)(struct rte_eth_dev *dev,
 				struct rte_dev_reg_info *info);
 /**< @internal Retrieve registers  */
@@ -496,6 +500,8 @@ struct eth_dev_ops {
 	eth_timesync_read_time     timesync_read_time; /** Get the device clock time. */
 	eth_timesync_write_time    timesync_write_time; /** Set the device clock time. */
 
+	eth_read_clock             read_clock;
+
 	eth_xstats_get_by_id_t     xstats_get_by_id;
 	/**< Get extended device statistic values by ID. */
 	eth_xstats_get_names_by_id_t xstats_get_names_by_id;
diff --git a/lib/librte_ethdev/rte_ethdev_version.map b/lib/librte_ethdev/rte_ethdev_version.map
index afcd25599..df9141825 100644
--- a/lib/librte_ethdev/rte_ethdev_version.map
+++ b/lib/librte_ethdev/rte_ethdev_version.map
@@ -253,6 +253,7 @@ EXPERIMENTAL {
 	rte_eth_dev_rx_intr_ctl_q_get_fd;
 	rte_eth_find_next_of;
 	rte_eth_find_next_sibling;
+	rte_eth_read_clock;
 	rte_eth_switch_domain_alloc;
 	rte_eth_switch_domain_free;
 	rte_flow_conv;
diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
index 68415af02..e530a96c5 100644
--- a/lib/librte_mbuf/rte_mbuf.h
+++ b/lib/librte_mbuf/rte_mbuf.h
@@ -668,6 +668,8 @@ struct rte_mbuf {
 
 	/** Valid if PKT_RX_TIMESTAMP is set. The unit and time reference
 	 * are not normalized but are always the same for a given port.
+	 * Some devices allow to query rte_eth_read_clock that will return the
+	 * current device timestamp.
 	 */
 	uint64_t timestamp;
 
-- 
2.17.1