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diff --git a/Documentation/driver-api/dpll.rst b/Documentation/driver-api/dpll.rst new file mode 100644 index 0000000000..e3d593841a --- /dev/null +++ b/Documentation/driver-api/dpll.rst @@ -0,0 +1,551 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=============================== +The Linux kernel dpll subsystem +=============================== + +DPLL +==== + +PLL - Phase Locked Loop is an electronic circuit which syntonizes clock +signal of a device with an external clock signal. Effectively enabling +device to run on the same clock signal beat as provided on a PLL input. + +DPLL - Digital Phase Locked Loop is an integrated circuit which in +addition to plain PLL behavior incorporates a digital phase detector +and may have digital divider in the loop. As a result, the frequency on +DPLL's input and output may be configurable. + +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 input 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. + +Device object +============= + +Single dpll device object means single Digital PLL circuit and bunch of +connected pins. +It reports the supported modes of operation and current status to the +user in response to the `do` request of netlink command +``DPLL_CMD_DEVICE_GET`` and list of dplls registered in the subsystem +with `dump` netlink request of the same command. +Changing the configuration of dpll device is done with `do` request of +netlink ``DPLL_CMD_DEVICE_SET`` command. +A device handle is ``DPLL_A_ID``, it shall be provided to get or set +configuration of particular device in the system. It can be obtained +with a ``DPLL_CMD_DEVICE_GET`` `dump` request or +a ``DPLL_CMD_DEVICE_ID_GET`` `do` request, where the one must provide +attributes that result in single device match. + +Pin object +========== + +A pin is amorphic object which represents either input or output, it +could be internal component of the device, as well as externally +connected. +The number of pins per dpll vary, but usually multiple pins shall be +provided for a single dpll device. +Pin's properties, capabilities and status is provided to the user in +response to `do` request of netlink ``DPLL_CMD_PIN_GET`` command. +It is also possible to list all the pins that were registered in the +system with `dump` request of ``DPLL_CMD_PIN_GET`` command. +Configuration of a pin can be changed by `do` request of netlink +``DPLL_CMD_PIN_SET`` command. +Pin handle is a ``DPLL_A_PIN_ID``, it shall be provided to get or set +configuration of particular pin in the system. It can be obtained with +``DPLL_CMD_PIN_GET`` `dump` request or ``DPLL_CMD_PIN_ID_GET`` `do` +request, where user provides attributes that result in single pin match. + +Pin selection +============= + +In general, selected pin (the one which signal is driving the dpll +device) can be obtained from ``DPLL_A_PIN_STATE`` attribute, and only +one pin shall be in ``DPLL_PIN_STATE_CONNECTED`` state for any dpll +device. + +Pin selection can be done either manually or automatically, depending +on hardware capabilities and active dpll device work mode +(``DPLL_A_MODE`` attribute). The consequence is that there are +differences for each mode in terms of available pin states, as well as +for the states the user can request for a dpll device. + +In manual mode (``DPLL_MODE_MANUAL``) the user can request or receive +one of following pin states: + +- ``DPLL_PIN_STATE_CONNECTED`` - the pin is used to drive dpll device +- ``DPLL_PIN_STATE_DISCONNECTED`` - the pin is not used to drive dpll + device + +In automatic mode (``DPLL_MODE_AUTOMATIC``) the user can request or +receive one of following pin states: + +- ``DPLL_PIN_STATE_SELECTABLE`` - the pin shall be considered as valid + input for automatic selection algorithm +- ``DPLL_PIN_STATE_DISCONNECTED`` - the pin shall be not considered as + a valid input for automatic selection algorithm + +In automatic mode (``DPLL_MODE_AUTOMATIC``) the user can only receive +pin state ``DPLL_PIN_STATE_CONNECTED`` once automatic selection +algorithm locks a dpll device with one of the inputs. + +Shared pins +=========== + +A single pin object can be attached to multiple dpll devices. +Then there are two groups of configuration knobs: + +1) Set on a pin - the configuration affects all dpll devices pin is + registered to (i.e., ``DPLL_A_PIN_FREQUENCY``), +2) Set on a pin-dpll tuple - the configuration affects only selected + dpll device (i.e., ``DPLL_A_PIN_PRIO``, ``DPLL_A_PIN_STATE``, + ``DPLL_A_PIN_DIRECTION``). + +MUX-type pins +============= + +A pin can be MUX-type, it aggregates child pins and serves as a pin +multiplexer. One or more pins are registered with MUX-type instead of +being directly registered to a dpll device. +Pins registered with a MUX-type pin provide user with additional nested +attribute ``DPLL_A_PIN_PARENT_PIN`` for each parent they were registered +with. +If a pin was registered with multiple parent pins, they behave like a +multiple output multiplexer. In this case output of a +``DPLL_CMD_PIN_GET`` would contain multiple pin-parent nested +attributes with current state related to each parent, like:: + + 'pin': [{{ + 'clock-id': 282574471561216, + 'module-name': 'ice', + 'capabilities': 4, + 'id': 13, + 'parent-pin': [ + {'parent-id': 2, 'state': 'connected'}, + {'parent-id': 3, 'state': 'disconnected'} + ], + 'type': 'synce-eth-port' + }}] + +Only one child pin can provide its signal to the parent MUX-type pin at +a time, the selection is done by requesting change of a child pin state +on desired parent, with the use of ``DPLL_A_PIN_PARENT`` nested +attribute. Example of netlink `set state on parent pin` message format: + + ========================== ============================================= + ``DPLL_A_PIN_ID`` child pin id + ``DPLL_A_PIN_PARENT_PIN`` nested attribute for requesting configuration + related to parent pin + ``DPLL_A_PIN_PARENT_ID`` parent pin id + ``DPLL_A_PIN_STATE`` requested pin state on parent + ========================== ============================================= + +Pin priority +============ + +Some devices might offer a capability of automatic pin selection mode +(enum value ``DPLL_MODE_AUTOMATIC`` of ``DPLL_A_MODE`` attribute). +Usually, automatic selection is performed on the hardware level, which +means only pins directly connected to the dpll can be used for automatic +input pin selection. +In automatic selection mode, the user cannot manually select a input +pin for the device, instead the user shall provide all directly +connected pins with a priority ``DPLL_A_PIN_PRIO``, the device would +pick a highest priority valid signal and use it to control the DPLL +device. Example of netlink `set priority on parent pin` message format: + + ============================ ============================================= + ``DPLL_A_PIN_ID`` configured pin id + ``DPLL_A_PIN_PARENT_DEVICE`` nested attribute for requesting configuration + related to parent dpll device + ``DPLL_A_PIN_PARENT_ID`` parent dpll device id + ``DPLL_A_PIN_PRIO`` requested pin prio on parent dpll + ============================ ============================================= + +Child pin of MUX-type pin is not capable of automatic input pin selection, +in order to configure active input of a MUX-type pin, the user needs to +request desired pin state of the child pin on the parent pin, +as described in the ``MUX-type pins`` chapter. + +Phase offset measurement and adjustment +======================================== + +Device may provide ability to measure a phase difference between signals +on a pin and its parent dpll device. If pin-dpll phase offset measurement +is supported, it shall be provided with ``DPLL_A_PIN_PHASE_OFFSET`` +attribute for each parent dpll device. + +Device may also provide ability to adjust a signal phase on a pin. +If pin phase adjustment is supported, minimal and maximal values that pin +handle shall be provide to the user on ``DPLL_CMD_PIN_GET`` respond +with ``DPLL_A_PIN_PHASE_ADJUST_MIN`` and ``DPLL_A_PIN_PHASE_ADJUST_MAX`` +attributes. Configured phase adjust value is provided with +``DPLL_A_PIN_PHASE_ADJUST`` attribute of a pin, and value change can be +requested with the same attribute with ``DPLL_CMD_PIN_SET`` command. + + =============================== ====================================== + ``DPLL_A_PIN_ID`` configured pin id + ``DPLL_A_PIN_PHASE_ADJUST_MIN`` attr minimum value of phase adjustment + ``DPLL_A_PIN_PHASE_ADJUST_MAX`` attr maximum value of phase adjustment + ``DPLL_A_PIN_PHASE_ADJUST`` attr configured value of phase + adjustment on parent dpll device + ``DPLL_A_PIN_PARENT_DEVICE`` nested attribute for requesting + configuration on given parent dpll + device + ``DPLL_A_PIN_PARENT_ID`` parent dpll device id + ``DPLL_A_PIN_PHASE_OFFSET`` attr measured phase difference + between a pin and parent dpll device + =============================== ====================================== + +All phase related values are provided in pico seconds, which represents +time difference between signals phase. The negative value means that +phase of signal on pin is earlier in time than dpll's signal. Positive +value means that phase of signal on pin is later in time than signal of +a dpll. + +Phase adjust (also min and max) values are integers, but measured phase +offset values are fractional with 3-digit decimal places and shell be +divided with ``DPLL_PIN_PHASE_OFFSET_DIVIDER`` to get integer part and +modulo divided to get fractional part. + +Configuration commands group +============================ + +Configuration commands are used to get information about registered +dpll devices (and pins), as well as set configuration of device or pins. +As dpll devices must be abstracted and reflect real hardware, +there is no way to add new dpll device via netlink from user space and +each device should be registered by its driver. + +All netlink commands require ``GENL_ADMIN_PERM``. This is to prevent +any spamming/DoS from unauthorized userspace applications. + +List of netlink commands with possible attributes +================================================= + +Constants identifying command types for dpll device uses a +``DPLL_CMD_`` prefix and suffix according to command purpose. +The dpll device related attributes use a ``DPLL_A_`` prefix and +suffix according to attribute purpose. + + ==================================== ================================= + ``DPLL_CMD_DEVICE_ID_GET`` command to get device ID + ``DPLL_A_MODULE_NAME`` attr module name of registerer + ``DPLL_A_CLOCK_ID`` attr Unique Clock Identifier + (EUI-64), as defined by the + IEEE 1588 standard + ``DPLL_A_TYPE`` attr type of dpll device + ==================================== ================================= + + ==================================== ================================= + ``DPLL_CMD_DEVICE_GET`` command to get device info or + dump list of available devices + ``DPLL_A_ID`` attr unique dpll device ID + ``DPLL_A_MODULE_NAME`` attr module name of registerer + ``DPLL_A_CLOCK_ID`` attr Unique Clock Identifier + (EUI-64), as defined by the + IEEE 1588 standard + ``DPLL_A_MODE`` attr selection mode + ``DPLL_A_MODE_SUPPORTED`` attr available selection modes + ``DPLL_A_LOCK_STATUS`` attr dpll device lock status + ``DPLL_A_TEMP`` attr device temperature info + ``DPLL_A_TYPE`` attr type of dpll device + ==================================== ================================= + + ==================================== ================================= + ``DPLL_CMD_DEVICE_SET`` command to set dpll device config + ``DPLL_A_ID`` attr internal dpll device index + ``DPLL_A_MODE`` attr selection mode to configure + ==================================== ================================= + +Constants identifying command types for pins uses a +``DPLL_CMD_PIN_`` prefix and suffix according to command purpose. +The pin related attributes use a ``DPLL_A_PIN_`` prefix and suffix +according to attribute purpose. + + ==================================== ================================= + ``DPLL_CMD_PIN_ID_GET`` command to get pin ID + ``DPLL_A_PIN_MODULE_NAME`` attr module name of registerer + ``DPLL_A_PIN_CLOCK_ID`` attr Unique Clock Identifier + (EUI-64), as defined by the + IEEE 1588 standard + ``DPLL_A_PIN_BOARD_LABEL`` attr pin board label provided + by registerer + ``DPLL_A_PIN_PANEL_LABEL`` attr pin panel label provided + by registerer + ``DPLL_A_PIN_PACKAGE_LABEL`` attr pin package label provided + by registerer + ``DPLL_A_PIN_TYPE`` attr type of a pin + ==================================== ================================= + + ==================================== ================================== + ``DPLL_CMD_PIN_GET`` command to get pin info or dump + list of available pins + ``DPLL_A_PIN_ID`` attr unique a pin ID + ``DPLL_A_PIN_MODULE_NAME`` attr module name of registerer + ``DPLL_A_PIN_CLOCK_ID`` attr Unique Clock Identifier + (EUI-64), as defined by the + IEEE 1588 standard + ``DPLL_A_PIN_BOARD_LABEL`` attr pin board label provided + by registerer + ``DPLL_A_PIN_PANEL_LABEL`` attr pin panel label provided + by registerer + ``DPLL_A_PIN_PACKAGE_LABEL`` attr pin package label provided + by registerer + ``DPLL_A_PIN_TYPE`` attr type of a pin + ``DPLL_A_PIN_FREQUENCY`` attr current frequency of a pin + ``DPLL_A_PIN_FREQUENCY_SUPPORTED`` nested attr provides supported + frequencies + ``DPLL_A_PIN_ANY_FREQUENCY_MIN`` attr minimum value of frequency + ``DPLL_A_PIN_ANY_FREQUENCY_MAX`` attr maximum value of frequency + ``DPLL_A_PIN_PHASE_ADJUST_MIN`` attr minimum value of phase + adjustment + ``DPLL_A_PIN_PHASE_ADJUST_MAX`` attr maximum value of phase + adjustment + ``DPLL_A_PIN_PHASE_ADJUST`` attr configured value of phase + adjustment on parent device + ``DPLL_A_PIN_PARENT_DEVICE`` nested attr for each parent device + the pin is connected with + ``DPLL_A_PIN_PARENT_ID`` attr parent dpll device id + ``DPLL_A_PIN_PRIO`` attr priority of pin on the + dpll device + ``DPLL_A_PIN_STATE`` attr state of pin on the parent + dpll device + ``DPLL_A_PIN_DIRECTION`` attr direction of a pin on the + parent dpll device + ``DPLL_A_PIN_PHASE_OFFSET`` attr measured phase difference + between a pin and parent dpll + ``DPLL_A_PIN_PARENT_PIN`` nested attr for each parent pin + the pin is connected with + ``DPLL_A_PIN_PARENT_ID`` attr parent pin id + ``DPLL_A_PIN_STATE`` attr state of pin on the parent + pin + ``DPLL_A_PIN_CAPABILITIES`` attr bitmask of pin capabilities + ==================================== ================================== + + ==================================== ================================= + ``DPLL_CMD_PIN_SET`` command to set pins configuration + ``DPLL_A_PIN_ID`` attr unique a pin ID + ``DPLL_A_PIN_FREQUENCY`` attr requested frequency of a pin + ``DPLL_A_PIN_PHASE_ADJUST`` attr requested value of phase + adjustment on parent device + ``DPLL_A_PIN_PARENT_DEVICE`` nested attr for each parent dpll + device configuration request + ``DPLL_A_PIN_PARENT_ID`` attr parent dpll device id + ``DPLL_A_PIN_DIRECTION`` attr requested direction of a pin + ``DPLL_A_PIN_PRIO`` attr requested priority of pin on + the dpll device + ``DPLL_A_PIN_STATE`` attr requested state of pin on + the dpll device + ``DPLL_A_PIN_PARENT_PIN`` nested attr for each parent pin + configuration request + ``DPLL_A_PIN_PARENT_ID`` attr parent pin id + ``DPLL_A_PIN_STATE`` attr requested state of pin on + parent pin + ==================================== ================================= + +Netlink dump requests +===================== + +The ``DPLL_CMD_DEVICE_GET`` and ``DPLL_CMD_PIN_GET`` commands are +capable of dump type netlink requests, in which case the response is in +the same format as for their ``do`` request, but every device or pin +registered in the system is returned. + +SET commands format +=================== + +``DPLL_CMD_DEVICE_SET`` - to target a dpll device, the user provides +``DPLL_A_ID``, which is unique identifier of dpll device in the system, +as well as parameter being configured (``DPLL_A_MODE``). + +``DPLL_CMD_PIN_SET`` - to target a pin user must provide a +``DPLL_A_PIN_ID``, which is unique identifier of a pin in the system. +Also configured pin parameters must be added. +If ``DPLL_A_PIN_FREQUENCY`` is configured, this affects all the dpll +devices that are connected with the pin, that is why frequency attribute +shall not be enclosed in ``DPLL_A_PIN_PARENT_DEVICE``. +Other attributes: ``DPLL_A_PIN_PRIO``, ``DPLL_A_PIN_STATE`` or +``DPLL_A_PIN_DIRECTION`` must be enclosed in +``DPLL_A_PIN_PARENT_DEVICE`` as their configuration relates to only one +of parent dplls, targeted by ``DPLL_A_PIN_PARENT_ID`` attribute which is +also required inside that nest. +For MUX-type pins the ``DPLL_A_PIN_STATE`` attribute is configured in +similar way, by enclosing required state in ``DPLL_A_PIN_PARENT_PIN`` +nested attribute and targeted parent pin id in ``DPLL_A_PIN_PARENT_ID``. + +In general, it is possible to configure multiple parameters at once, but +internally each parameter change will be invoked separately, where order +of configuration is not guaranteed by any means. + +Configuration pre-defined enums +=============================== + +.. kernel-doc:: include/uapi/linux/dpll.h + +Notifications +============= + +dpll device can provide notifications regarding status changes of the +device, i.e. lock status changes, input/output changes or other alarms. +There is one multicast group that is used to notify user-space apps via +netlink socket: ``DPLL_MCGRP_MONITOR`` + +Notifications messages: + + ============================== ===================================== + ``DPLL_CMD_DEVICE_CREATE_NTF`` dpll device was created + ``DPLL_CMD_DEVICE_DELETE_NTF`` dpll device was deleted + ``DPLL_CMD_DEVICE_CHANGE_NTF`` dpll device has changed + ``DPLL_CMD_PIN_CREATE_NTF`` dpll pin was created + ``DPLL_CMD_PIN_DELETE_NTF`` dpll pin was deleted + ``DPLL_CMD_PIN_CHANGE_NTF`` dpll pin has changed + ============================== ===================================== + +Events format is the same as for the corresponding get command. +Format of ``DPLL_CMD_DEVICE_`` events is the same as response of +``DPLL_CMD_DEVICE_GET``. +Format of ``DPLL_CMD_PIN_`` events is same as response of +``DPLL_CMD_PIN_GET``. + +Device driver implementation +============================ + +Device is allocated by dpll_device_get() call. Second call with the +same arguments will not create new object but provides pointer to +previously created device for given arguments, it also increases +refcount of that object. +Device is deallocated by dpll_device_put() call, which first +decreases the refcount, once refcount is cleared the object is +destroyed. + +Device should implement set of operations and register device via +dpll_device_register() at which point it becomes available to the +users. Multiple driver instances can obtain reference to it with +dpll_device_get(), as well as register dpll device with their own +ops and priv. + +The pins are allocated separately with dpll_pin_get(), it works +similarly to dpll_device_get(). Function first creates object and then +for each call with the same arguments only the object refcount +increases. Also dpll_pin_put() works similarly to dpll_device_put(). + +A pin can be registered with parent dpll device or parent pin, depending +on hardware needs. Each registration requires registerer to provide set +of pin callbacks, and private data pointer for calling them: + +- dpll_pin_register() - register pin with a dpll device, +- dpll_pin_on_pin_register() - register pin with another MUX type pin. + +Notifications of adding or removing dpll devices are created within +subsystem itself. +Notifications about registering/deregistering pins are also invoked by +the subsystem. +Notifications about status changes either of dpll device or a pin are +invoked in two ways: + +- after successful change was requested on dpll subsystem, the subsystem + calls corresponding notification, +- requested by device driver with dpll_device_change_ntf() or + dpll_pin_change_ntf() when driver informs about the status change. + +The device driver using dpll interface is not required to implement all +the callback operation. Nevertheless, there are few required to be +implemented. +Required dpll device level callback operations: + +- ``.mode_get``, +- ``.lock_status_get``. + +Required pin level callback operations: + +- ``.state_on_dpll_get`` (pins registered with dpll device), +- ``.state_on_pin_get`` (pins registered with parent pin), +- ``.direction_get``. + +Every other operation handler is checked for existence and +``-EOPNOTSUPP`` is returned in case of absence of specific handler. + +The simplest implementation is in the OCP TimeCard driver. The ops +structures are defined like this: + +.. code-block:: c + + static const struct dpll_device_ops dpll_ops = { + .lock_status_get = ptp_ocp_dpll_lock_status_get, + .mode_get = ptp_ocp_dpll_mode_get, + .mode_supported = ptp_ocp_dpll_mode_supported, + }; + + static const struct dpll_pin_ops dpll_pins_ops = { + .frequency_get = ptp_ocp_dpll_frequency_get, + .frequency_set = ptp_ocp_dpll_frequency_set, + .direction_get = ptp_ocp_dpll_direction_get, + .direction_set = ptp_ocp_dpll_direction_set, + .state_on_dpll_get = ptp_ocp_dpll_state_get, + }; + +The registration part is then looks like this part: + +.. code-block:: c + + clkid = pci_get_dsn(pdev); + bp->dpll = dpll_device_get(clkid, 0, THIS_MODULE); + if (IS_ERR(bp->dpll)) { + err = PTR_ERR(bp->dpll); + dev_err(&pdev->dev, "dpll_device_alloc failed\n"); + goto out; + } + + err = dpll_device_register(bp->dpll, DPLL_TYPE_PPS, &dpll_ops, bp); + if (err) + goto out; + + for (i = 0; i < OCP_SMA_NUM; i++) { + bp->sma[i].dpll_pin = dpll_pin_get(clkid, i, THIS_MODULE, &bp->sma[i].dpll_prop); + if (IS_ERR(bp->sma[i].dpll_pin)) { + err = PTR_ERR(bp->dpll); + goto out_dpll; + } + + err = dpll_pin_register(bp->dpll, bp->sma[i].dpll_pin, &dpll_pins_ops, + &bp->sma[i]); + if (err) { + dpll_pin_put(bp->sma[i].dpll_pin); + goto out_dpll; + } + } + +In the error path we have to rewind every allocation in the reverse order: + +.. code-block:: c + + while (i) { + --i; + dpll_pin_unregister(bp->dpll, bp->sma[i].dpll_pin, &dpll_pins_ops, &bp->sma[i]); + dpll_pin_put(bp->sma[i].dpll_pin); + } + dpll_device_put(bp->dpll); + +More complex example can be found in Intel's ICE driver or nVidia's mlx5 driver. + +SyncE enablement +================ +For SyncE enablement it is required to allow control over dpll device +for a software application which monitors and configures the inputs of +dpll device in response to current state of a dpll device and its +inputs. +In such scenario, dpll device input signal shall be also configurable +to drive dpll with signal recovered from the PHY netdevice. +This is done by exposing a pin to the netdevice - attaching pin to the +netdevice itself with +``netdev_dpll_pin_set(struct net_device *dev, struct dpll_pin *dpll_pin)``. +Exposed pin id handle ``DPLL_A_PIN_ID`` is then identifiable by the user +as it is attached to rtnetlink respond to get ``RTM_NEWLINK`` command in +nested attribute ``IFLA_DPLL_PIN``. |