[RFC PATCH v5 2/4] dpll: documentation on DPLL subsystem interface

Vadim Fedorenko
2023-01-17T18:02:55Z

Add documentation explaining common netlink interface to configure DPLL
devices and monitoring events. Common way to implement DPLL device in
a driver is also covered.

Co-developed-by: Arkadiusz Kubalewski <arkadiusz.kubalewski@intel.com>
Signed-off-by: Arkadiusz Kubalewski <arkadiusz.kubalewski@intel.com>
Signed-off-by: Vadim Fedorenko <vadfed@meta.com>
---
Documentation/networking/dpll.rst | 280 +++++++++++++++++++++++++++++
Documentation/networking/index.rst | 1 +
2 files changed, 281 insertions(+)
create mode 100644 Documentation/networking/dpll.rst

diff --git a/Documentation/networking/dpll.rst b/Documentation/networking/dpll.rst
new file mode 100644
index 000000000000..bd4d5f9f60ce
--- /dev/null
+++ b/Documentation/networking/dpll.rst
@@ -0,0 +1,280 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===============================
+The Linux kernel DPLL subsystem
+===============================
+
+
+The main purpose of DPLL subsystem is to provide general interface
+to configure devices that use any kind of Digital PLL and could use
+different sources of signal to synchronize to as well as different
+types of outputs.
+The main interface is NETLINK_GENERIC based protocol with an event
+monitoring multicast group defined.
+
+
+Pin object
+==========
+A pin is amorphic object which represents either input and output, it
+could be internal component of the device, as well as externaly
+connected.
+The number of pins per dpll vary, but usually multiple pins shall be
+provided for a single dpll device.
+Direction of a pin and it's capabilities are provided to the user in
+response for netlink dump request messages.
+Pin can be shared by multiple dpll devices. Where configuration on one
+pin can alter multiple dplls (i.e. DPLL_PIN_SIGNAL_TYPE, DPLL_PIN_MODE),
+or just one pin-dpll pair (i.e. DPLL_PIN_PRIO).
+Pin can be also a MUX type, where one or more pins are attached to
+a parent pin. The parent pin is the one directly connected to the dpll,
+which may be used by dplls in DPLL_MODE_AUTOMATIC selection mode, where
+only pins directly connected to the dpll are capable of automatic
+source pin selection. In such case, pins are dumped with
+DPLLA_PIN_PARENT_IDX, and are able to be selected by the userspace with
+netlink request.
+
+Configuration commands group
+============================
+
+Configuration commands are used to get or dump information about
+registered DPLL devices (and pins), as well as set configuration of
+device or pins. As DPLL device could not be abstract and reflects real
+hardware, there is no way to add new DPLL device via netlink from user
+space and each device should be registered by it's driver.
+
+All netlink commands require ``GENL_UNS_ADMIN_PERM``. This is to prevent
+any spamming/D.o.S. from unauthorized userspace applications.
+
+List of command with possible attributes
+========================================
+
+All constants identifying command types use ``DPLL_CMD_`` prefix and
+suffix according to command purpose. All attributes use ``DPLLA_``
+prefix and suffix according to attribute purpose:
+
+ ============================ =======================================
+ ``DEVICE_GET`` userspace to get device info
+ ``ID`` attr internal dpll device index
+ ``NAME`` attr dpll device name
+ ``MODE`` attr selection mode
+ ``MODE_SUPPORTED`` attr available selection modes
+ ``SOURCE_PIN_IDX`` attr index of currently selected source
+ ``LOCK_STATUS`` attr internal frequency-lock status
+ ``TEMP`` attr device temperature information
+ ``CLOCK_ID`` attr Unique Clock Identifier (EUI-64),
+ as defined by the IEEE 1588 standard
+ ``CLOCK_CLASS`` attr clock class, as defined in
+ recommendation ITU-T G.8273.2/Y.1368.2
+ ``FILTER`` attr for filtering dump or get requests
+ ``DEVICE_SET`` userspace to set dpll device
+ configuration
+ ``ID`` attr internal dpll device index
+ ``NAME`` attr dpll device name (not required if
+ dpll device index was provided)
+ ``MODE`` attr selection mode to configure
+ ``PIN_IDX`` attr index of source pin to select as
+ active source
+ ``PIN_SET`` userspace to set pins configuration
+ ``ID`` attr internal dpll device index
+ ``NAME`` attr dpll device name (not required if
+ dpll device index was provided)
+ ``PIN_IDX`` attr index of a pin to configure
+ ``PIN_SIGNAL_TYPE`` attr signal type configuration value
+ for selected pin
+ ``PIN_CUSTOM_FREQ`` attr signal custom frequency to be set
+ ``PIN_MODE`` attr pin mode to be set
+ ``PIN_PRIO`` attr pin priority to be set
+
+Netlink dump requests
+=====================
+All below attributes of dump requests use ``DPLLA_`` prefix.
+
+The ``DEVICE_GET`` command is capable of dump type netlink requests.
+In such case the userspace shall provide ``FILTER`` attribute
+value to filter the response as required.
+If filter is not provided only name and id of available dpll(s) is
+provided. If the request also contains ``ID`` attribute, only selected
+dpll device shall be dumped.
+
+Possible response message attributes for netlink requests depending on
+the value of ``FILTER`` attribute:
+
+ =============================== ====================================
+ ``DPLL_FILTER_PINS`` value of ``FILTER`` attribute
+ ``PIN`` attr nested type contain single pin
+ attributes
+ ``PIN_IDX`` attr index of dumped pin
+ ``PIN_DESCRIPTION`` description of a pin provided by
+ driver
+ ``PIN_TYPE`` attr value of pin type
+ ``PIN_SIGNAL_TYPE`` attr value of pin signal type
+ ``PIN_SIGNAL_TYPE_SUPPORTED`` attr value of supported pin signal
+ type
+ ``PIN_CUSTOM_FREQ`` attr value of pin custom frequency
+ ``PIN_MODE`` attr value of pin mode
+ ``PIN_MODE_SUPPORTED`` attr value of supported pin modes
+ ``PIN_PRIO`` attr value of pin prio
+ ``PIN_PARENT_IDX`` attr value of pin patent index
+ ``PIN_NETIFINDEX`` attr value of netdevice assocaiated
+ with the pin
+ ``DPLL_FILTER_STATUS`` value of ``FILTER`` attribute
+ ``ID`` attr internal dpll device index
+ ``NAME`` attr dpll device name
+ ``MODE`` attr selection mode
+ ``MODE_SUPPORTED`` attr available selection modes
+ ``SOURCE_PIN_IDX`` attr index of currently selected
+ source
+ ``LOCK_STATUS`` attr internal frequency-lock status
+ ``TEMP`` attr device temperature information
+ ``CLOCK_ID`` attr Unique Clock Identifier (EUI-64),
+ as defined by the IEEE 1588 standard
+ ``CLOCK_CLASS`` attr clock class, as defined in
+ recommendation ITU-T G.8273.2/Y.1368.2
+
+
+The pre-defined enums
+=====================
+
+All the enums use the ``DPLL_`` prefix.
+
+Values for ``PIN_TYPE`` and ``PIN_TYPE_SUPPORTED`` attributes:
+
+ ============================ ========================================
+ ``PIN_TYPE_MUX`` MUX type pin, connected pins shall
+ have their own types
+ ``PIN_TYPE_EXT`` External pin
+ ``PIN_TYPE_SYNCE_ETH_PORT`` SyncE on Ethernet port
+ ``PIN_TYPE_INT_OSCILLATOR`` Internal Oscillator (i.e. Holdover
+ with Atomic Clock as a Source)
+ ``PIN_TYPE_GNSS`` GNSS 1PPS source
+
+Values for ``PIN_SIGNAL_TYPE`` and ``PIN_SIGNAL_TYPE_SUPPORTED``
+attributes:
+
+ =============================== ===================================
+ ``PIN_SIGNAL_TYPE_1_PPS`` 1 Hz frequency
+ ``PIN_SIGNAL_TYPE_10_MHZ`` 10 MHz frequency
+ ``PIN_SIGNAL_TYPE_CUSTOM_FREQ`` Frequency value provided in attr
+ ``PIN_CUSTOM_FREQ``
+
+Values for ``LOCK_STATUS`` attribute:
+
+ ============================= ======================================
+ ``LOCK_STATUS_UNLOCKED`` DPLL is in freerun, not locked to any
+ source pin
+ ``LOCK_STATUS_CALIBRATING`` DPLL device calibrates to lock to the
+ source pin signal
+ ``LOCK_STATUS_LOCKED`` DPLL device is locked to the source
+ pin frequency
+ ``LOCK_STATUS_HOLDOVER`` DPLL device lost a lock, using its
+ frequency holdover capabilities
+
+Values for ``PIN_MODE`` and ``PIN_STATE_SUPPORTED`` attributes:
+
+============================= ============================
+ ``PIN_MODE_CONNECTED`` Pin connected to a dpll
+ ``PIN_MODE_DISCONNECTED`` Pin disconnected from dpll
+ ``PIN_MODE_SOURCE`` Source pin
+ ``PIN_MODE_OUTPUT`` Output pin
+
+Possible DPLL source selection mode values:
+
+ =================== ================================================
+ ``MODE_FORCED`` source pin is force-selected by
+ ``DPLL_CMD_DEVICE_SET`` with given value of
+ ``DPLLA_SOURCE_PIN_IDX`` attribute
+ ``MODE_AUTOMATIC`` source pin is auto selected according to
+ configured pin priorities and source signal
+ validity
+ ``MODE_HOLDOVER`` force holdover mode of DPLL
+ ``MODE_FREERUN`` DPLL is driven by supplied system clock without
+ holdover capabilities
+ ``MODE_NCO`` similar to FREERUN, with possibility to
+ numerically control frequency offset
+
+Notifications
+================
+
+DPLL device can provide notifications regarding status changes of the
+device, i.e. lock status changes, source/output type changes or alarms.
+This is the multicast group that is used to notify user-space apps via
+netlink socket:
+
+Notifications messages:
+
+ ========================= ==========================================
+ ``EVENT_DEVICE_CREATE`` event value new DPLL device was created
+ ``ID`` attr dpll device index
+ ``NAME`` attr dpll device name
+ ``EVENT_DEVICE_DELETE`` event value DPLL device was deleted
+ ``ID`` attr dpll device index
+ ``EVENT_DEVICE_CHANGE`` event value DPLL device attribute has changed
+ ``ID`` attr dpll device index
+ ``CHANGE_TYPE`` attr the reason for change with values of
+ ``enum dpll_event_change``
+
+Device change event reasons, values of ``CHANGE_TYPE`` attribute:
+
+ =========================== =========================================
+ ``CHANGE_MODE`` DPLL selection mode has changed
+ ``CHANGE_LOCK_STATUS`` DPLL lock status has changed
+ ``CHANGE_SOURCE_PIN`` DPLL source pin has changed
+ ``CHANGE_TEMP`` DPLL temperature has changed
+ ``CHANGE_PIN_ADD`` pin added to DPLL
+ ``CHANGE_PIN_DEL`` pin removed from DPLL
+ ``CHANGE_PIN_SIGNAL_TYPE`` pin signal type has changed
+ ``CHANGE_PIN_CUSTOM_FREQ`` pin custom frequency value has changed
+ ``CHANGE_PIN_MODE`` pin mode has changed
+ ``CHANGE_PIN_PRIO`` pin prio has changed
+
+
+Device driver implementation
+============================
+
+For device to operate as DPLL subsystem device, it should implement
+set of operations and register device via ``dpll_device_alloc``,
+provide the operations set, unique device clock_id, class of a clock,
+type of dpll (PPS/EEC), pointer to parent device and pointer to its
+private data, that can be used in callback ops.
+
+The pins are allocated separately with ``dpll_pin_alloc``, which
+requires providing pin description and its type.
+
+Once DPLL device is created, allocated pin can be registered with it
+with 2 different methods, always providing implemented pin callbacks,
+and private data pointer for calling them:
+``dpll_pin_register`` - simple registration with a dpll device.
+``dpll_muxed_pin_register`` - register pin with another MUX type pin.
+
+It is also possible to register pin already registered with different
+DPLL device by calling ``dpll_shared_pin_register`` - in this case
+changes requested on a single pin would affect all DPLLs which were
+registered with that pin.
+
+For different instances of a device driver requiring to find already
+registered DPLL (i.e. to connect its pins to id)
+use ``dpll_device_get_by_clock_id`` providing the same clock_id, type of
+dpll and index of the DPLL device of such type, same as given on
+original device allocation.
+
+The name od DPLL device is generated based on registerer device struct
+pointer, DPLL type and an index received from registerer device driver.
+Name is in format: ``dpll_%s_%d_%d`` witch arguments:
+``dev_name(parent)`` - syscall on parent device
+``type`` - DPLL type converted to string
+``dev_driver_idx`` - registerer given index
+
+Notifications of adding or removing DPLL devices are created within
+subsystem itself.
+Notifications about registering/deregistering pins are also invoked by
+the subsystem.
+Any other change notifications shall be requested by device driver with
+``dpll_device_notify`` or ``dpll_pin_notify`` and corresponding reason.
+Change reason enums ``dpll_event_change`` are defined in
+``<linux/dpll.h>``, constants and enums are placed in
+``<uapi/linux/dpll.h>`` to be consistent with user-space.
+
+There is no strict requirement to implement all the operations for
+each device, every operation handler is checked for existence and
+ENOTSUPP is returned in case of absence of specific handler.
+
diff --git a/Documentation/networking/index.rst b/Documentation/networking/index.rst
index 4f2d1f682a18..d50d98939942 100644
--- a/Documentation/networking/index.rst
+++ b/Documentation/networking/index.rst
@@ -16,6 +16,7 @@ Contents:
device_drivers/index
dsa/index
devlink/index
+ dpll
caif/index
ethtool-netlink
ieee802154
--
2.30.2