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net: ena: Add PHC documentation

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Provide the relevant information and guidelines
about the feature support in the ENA driver.

Signed-off-by: Amit Bernstein <amitbern@amazon.com>
Signed-off-by: David Arinzon <darinzon@amazon.com>
Link: https://patch.msgid.link/20250617110545.5659-10-darinzon@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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David Arinzon 2025-06-17 14:05:45 +03:00 committed by Jakub Kicinski
parent e14521e97b
commit c922302143
1 changed files with 93 additions and 0 deletions
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Documentation/networking/device_drivers/ethernet/amazon/ena.rst
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@ -224,6 +224,99 @@ descriptor it was received on would be recycled. When a packet smaller
than RX copybreak bytes is received, it is copied into a new memory
buffer and the RX descriptor is returned to HW.
.. _`PHC`:
PTP Hardware Clock (PHC)
========================
.. _`ptp-userspace-api`: https://docs.kernel.org/driver-api/ptp.html#ptp-hardware-clock-user-space-api
.. _`testptp`: https://elixir.bootlin.com/linux/latest/source/tools/testing/selftests/ptp/testptp.c
ENA Linux driver supports PTP hardware clock providing timestamp reference to achieve nanosecond resolution.
**PHC support**
PHC depends on the PTP module, which needs to be either loaded as a module or compiled into the kernel.
Verify if the PTP module is present:
.. code-block:: shell
grep -w '^CONFIG_PTP_1588_CLOCK=[ym]' /boot/config-`uname -r`
- If no output is provided, the ENA driver cannot be loaded with PHC support.
**PHC activation**
The feature is turned off by default, in order to turn the feature on, the ENA driver
can be loaded in the following way:
- devlink:
.. code-block:: shell
sudo devlink dev param set pci/<domain:bus:slot.function> name enable_phc value true cmode driverinit
sudo devlink dev reload pci/<domain:bus:slot.function>
# for example:
sudo devlink dev param set pci/0000:00:06.0 name enable_phc value true cmode driverinit
sudo devlink dev reload pci/0000:00:06.0
All available PTP clock sources can be tracked here:
.. code-block:: shell
ls /sys/class/ptp
PHC support and capabilities can be verified using ethtool:
.. code-block:: shell
ethtool -T <interface>
**PHC timestamp**
To retrieve PHC timestamp, use `ptp-userspace-api`_, usage example using `testptp`_:
.. code-block:: shell
testptp -d /dev/ptp$(ethtool -T <interface> | awk '/PTP Hardware Clock:/ {print $NF}') -k 1
PHC get time requests should be within reasonable bounds,
avoid excessive utilization to ensure optimal performance and efficiency.
The ENA device restricts the frequency of PHC get time requests to a maximum
of 125 requests per second. If this limit is surpassed, the get time request
will fail, leading to an increment in the phc_err_ts statistic.
**PHC statistics**
PHC can be monitored using debugfs (if mounted):
.. code-block:: shell
sudo cat /sys/kernel/debug/<domain:bus:slot.function>/phc_stats
# for example:
sudo cat /sys/kernel/debug/0000:00:06.0/phc_stats
PHC errors must remain below 1% of all PHC requests to maintain the desired level of accuracy and reliability
================= ======================================================
**phc_cnt** | Number of successful retrieved timestamps (below expire timeout).
**phc_exp** | Number of expired retrieved timestamps (above expire timeout).
**phc_skp** | Number of skipped get time attempts (during block period).
**phc_err_dv** | Number of failed get time attempts due to device errors (entering into block state).
**phc_err_ts** | Number of failed get time attempts due to timestamp errors (entering into block state),
| This occurs if driver exceeded the request limit or device received an invalid timestamp.
================= ======================================================
PHC timeouts:
================= ======================================================
**expire** | Max time for a valid timestamp retrieval, passing this threshold will fail
| the get time request and block new requests until block timeout.
**block** | Blocking period starts once get time request expires or fails,
| all get time requests during block period will be skipped.
================= ======================================================
Statistics
==========