diff --git a/Documentation/components/drivers/special/ptp.rst b/Documentation/components/drivers/special/ptp.rst
index 0bacee1f2e4..5e592ef9196 100644
--- a/Documentation/components/drivers/special/ptp.rst
+++ b/Documentation/components/drivers/special/ptp.rst
@@ -496,6 +496,24 @@ that embeds a ``struct ptp_lowerhalf_s`` and provides the operations of
      return ptp_clock_register(&priv->base, 500000, 0);
    }
 
+Existing Implementations
+========================
+
+The following lower-half drivers are available in the tree:
+
+- ``drivers/timers/ptp_clock_dummy.c`` - The dummy driver described above,
+  enabled with ``CONFIG_PTP_CLOCK_DUMMY``. It is registered as ``/dev/ptp0``
+  at start-up.
+- ``arch/arm/src/common/stm32/stm32_eth_m3m4_v1.c`` - The Ethernet MAC of the
+  STM32 (the legacy driver), registered with ``CONFIG_PTP_CLOCK`` and
+  ``CONFIG_STM32_ETH_PTP`` as ``/dev/ptpN``, where N is the number of the
+  Ethernet interface. The clock is the PTP counter of the MAC. It is also the
+  time base of the hardware timestamps of the received packets, so those are
+  not values of ``CLOCK_REALTIME``.
+
+Both use the device number 0 by default, so they cannot be registered at the
+same time.
+
 Integration with PTP Daemon
 ===========================