RE: [RFC PATCH v4 3/4] dpll: documentation on DPLL subsystem interface

Kubalewski, Arkadiusz
2023-01-12T13:45:17Z

>From: Paolo Abeni <pabeni@redhat.com>
>Sent: Monday, December 19, 2022 10:13 AM
>
>Hello,
>
>I have a just a few minor notes WRT the documentation - which was a
>very useful entry point for me to help understanding the subsystem.

Hi Paolo, many thanks for your feedback!

>
>On Wed, 2022-11-30 at 00:37 +0300, Vadim Fedorenko wrote:
>> From: Vadim Fedorenko <vadfed@fb.com>
>>
>> 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@fb.com>
>> ---
>> Documentation/networking/dpll.rst | 271 +++++++++++++++++++++++++++++
>> Documentation/networking/index.rst | 1 +
>> 2 files changed, 272 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..58401e2b70a7
>> --- /dev/null
>> +++ b/Documentation/networking/dpll.rst
>> @@ -0,0 +1,271 @@
>> +.. 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_SGINAL_TYPE, DPLL_PIN_TYPE,
>
>Likely typo above: DPLL_PIN_SIGNAL_TYPE

True, shall be fixed in next version.

>
>> +DPLL_PIN_STATE), 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.
>
>Side note: in the long run we could end-up with a virtual/dummy dpll
>driver for self-tests and/or reference's implementation sake.
>

True, seems a good idea.

>> +
>> +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
>> + ``NETIFINDEX`` attr dpll owner Linux netdevice index
>
>should we include also the cookie (or wuhatever will be used for
>persistent device identification) into the readable attributes list?
>

In next version cookie is replaced with clock_id and will be also available
for the userspace.

>> + ``DEVICE_SET`` userspace to set dpll device
>> + configuration
>> + ``ID`` attr internal dpll device index
>> + ``MODE`` attr selection mode to configure
>> + ``PIN_IDX`` attr index of source pin to select as
>> + active source
>
>It looks like the descrition for the above attribute ('PIN_IDX') and
>'SOURCE_PIN_IDX' has been swapped.

Good catch, for ``DEVICE_SET`` command, proper attribute is 'SOURCE_PIN_IDX',
will fix that.

>
>> + ``PIN_SET`` userspace to set pins configuration
>> + ``ID`` attr internal dpll device index
>> + ``PIN_IDX`` attr index of a pin to configure
>> + ``PIN_TYPE`` attr type configuration value for
>> + selected pin
>> + ``PIN_SIGNAL_TYPE`` attr signal type configuration value
>> + for selected pin
>> + ``PIN_CUSTOM_FREQ`` attr signal custom frequency to be set
>> + ``PIN_STATE`` attr pin state to be set
>> + ``PIN_PRIO`` attr pin priority to be set
>> +
>> +Netlink dump requests
>> +=====================
>> +The ``DEVICE_GET`` command is capable of dump type netlink requests.
>> +In such case the userspace shall provide ``DUMP_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.
>
>Should we explicitly document even the required permissions?

Sure, going to add a word about required netlink permission.

>
>> +
>> +Possible response message attributes for netlink requests depending on
>> +the value of ``DPLLA_DUMP_FILTER`` attribute:
>> +
>> + =============================== ====================================
>> + ``DPLL_DUMP_FILTER_PINS`` value of ``DUMP_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_TYPE_SUPPORTED`` attr value of supported 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_STATE`` attr value of pin state
>> + ``PIN_STATE_SUPPORTED`` attr value of supported pin state
>> + ``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_DUMP_FILTER_STATUS`` value of ``DUMP_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
>> + ``NETIFINDEX`` attr dpll owner Linux netdevice index
>> +
>> +
>> +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_STATE`` and ``PIN_STATE_SUPPORTED`` attributes:
>> +
>> +============================= ============================
>> + ``PIN_STATE_CONNECTED`` Pin connected to a dpll
>> + ``PIN_STATE_DISCONNECTED`` Pin disconnected from dpll
>> + ``PIN_STATE_SOURCE`` Source pin
>> + ``PIN_STATE_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 ise auto selected according to
>
>typo above 'ise' -> 'is'
>

Sure, will fix.

Thanks again!

BR,
Arkadiusz

>
>Cheers,
>
>Paolo