205 lines
7.9 KiB
ReStructuredText
205 lines
7.9 KiB
ReStructuredText
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.. SPDX-License-Identifier: GPL-2.0+
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.. |ssam_cdev_request| replace:: :c:type:`struct ssam_cdev_request <ssam_cdev_request>`
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.. |ssam_cdev_request_flags| replace:: :c:type:`enum ssam_cdev_request_flags <ssam_cdev_request_flags>`
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.. |ssam_cdev_event| replace:: :c:type:`struct ssam_cdev_event <ssam_cdev_event>`
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==============================
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User-Space EC Interface (cdev)
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==============================
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The ``surface_aggregator_cdev`` module provides a misc-device for the SSAM
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controller to allow for a (more or less) direct connection from user-space to
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the SAM EC. It is intended to be used for development and debugging, and
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therefore should not be used or relied upon in any other way. Note that this
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module is not loaded automatically, but instead must be loaded manually.
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The provided interface is accessible through the ``/dev/surface/aggregator``
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device-file. All functionality of this interface is provided via IOCTLs.
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These IOCTLs and their respective input/output parameter structs are defined in
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``include/uapi/linux/surface_aggregator/cdev.h``.
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A small python library and scripts for accessing this interface can be found
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at https://github.com/linux-surface/surface-aggregator-module/tree/master/scripts/ssam.
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.. contents::
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Receiving Events
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================
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Events can be received by reading from the device-file. The are represented by
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the |ssam_cdev_event| datatype.
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Before events are available to be read, however, the desired notifiers must be
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registered via the ``SSAM_CDEV_NOTIF_REGISTER`` IOCTL. Notifiers are, in
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essence, callbacks, called when the EC sends an event. They are, in this
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interface, associated with a specific target category and device-file-instance.
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They forward any event of this category to the buffer of the corresponding
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instance, from which it can then be read.
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Notifiers themselves do not enable events on the EC. Thus, it may additionally
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be necessary to enable events via the ``SSAM_CDEV_EVENT_ENABLE`` IOCTL. While
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notifiers work per-client (i.e. per-device-file-instance), events are enabled
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globally, for the EC and all of its clients (regardless of userspace or
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non-userspace). The ``SSAM_CDEV_EVENT_ENABLE`` and ``SSAM_CDEV_EVENT_DISABLE``
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IOCTLs take care of reference counting the events, such that an event is
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enabled as long as there is a client that has requested it.
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Note that enabled events are not automatically disabled once the client
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instance is closed. Therefore any client process (or group of processes) should
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balance their event enable calls with the corresponding event disable calls. It
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is, however, perfectly valid to enable and disable events on different client
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instances. For example, it is valid to set up notifiers and read events on
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client instance ``A``, enable those events on instance ``B`` (note that these
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will also be received by A since events are enabled/disabled globally), and
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after no more events are desired, disable the previously enabled events via
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instance ``C``.
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Controller IOCTLs
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=================
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The following IOCTLs are provided:
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.. flat-table:: Controller IOCTLs
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:widths: 1 1 1 1 4
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:header-rows: 1
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* - Type
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- Number
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- Direction
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- Name
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- Description
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* - ``0xA5``
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- ``1``
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- ``WR``
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- ``REQUEST``
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- Perform synchronous SAM request.
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* - ``0xA5``
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- ``2``
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- ``W``
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- ``NOTIF_REGISTER``
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- Register event notifier.
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* - ``0xA5``
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- ``3``
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- ``W``
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- ``NOTIF_UNREGISTER``
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- Unregister event notifier.
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* - ``0xA5``
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- ``4``
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- ``W``
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- ``EVENT_ENABLE``
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- Enable event source.
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* - ``0xA5``
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- ``5``
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- ``W``
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- ``EVENT_DISABLE``
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- Disable event source.
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``SSAM_CDEV_REQUEST``
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---------------------
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Defined as ``_IOWR(0xA5, 1, struct ssam_cdev_request)``.
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Executes a synchronous SAM request. The request specification is passed in
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as argument of type |ssam_cdev_request|, which is then written to/modified
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by the IOCTL to return status and result of the request.
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Request payload data must be allocated separately and is passed in via the
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``payload.data`` and ``payload.length`` members. If a response is required,
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the response buffer must be allocated by the caller and passed in via the
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``response.data`` member. The ``response.length`` member must be set to the
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capacity of this buffer, or if no response is required, zero. Upon
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completion of the request, the call will write the response to the response
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buffer (if its capacity allows it) and overwrite the length field with the
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actual size of the response, in bytes.
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Additionally, if the request has a response, this must be indicated via the
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request flags, as is done with in-kernel requests. Request flags can be set
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via the ``flags`` member and the values correspond to the values found in
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|ssam_cdev_request_flags|.
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Finally, the status of the request itself is returned in the ``status``
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member (a negative errno value indicating failure). Note that failure
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indication of the IOCTL is separated from failure indication of the request:
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The IOCTL returns a negative status code if anything failed during setup of
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the request (``-EFAULT``) or if the provided argument or any of its fields
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are invalid (``-EINVAL``). In this case, the status value of the request
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argument may be set, providing more detail on what went wrong (e.g.
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``-ENOMEM`` for out-of-memory), but this value may also be zero. The IOCTL
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will return with a zero status code in case the request has been set up,
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submitted, and completed (i.e. handed back to user-space) successfully from
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inside the IOCTL, but the request ``status`` member may still be negative in
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case the actual execution of the request failed after it has been submitted.
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A full definition of the argument struct is provided below.
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``SSAM_CDEV_NOTIF_REGISTER``
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----------------------------
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Defined as ``_IOW(0xA5, 2, struct ssam_cdev_notifier_desc)``.
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Register a notifier for the event target category specified in the given
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notifier description with the specified priority. Notifiers registration is
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required to receive events, but does not enable events themselves. After a
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notifier for a specific target category has been registered, all events of that
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category will be forwarded to the userspace client and can then be read from
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the device file instance. Note that events may have to be enabled, e.g. via the
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``SSAM_CDEV_EVENT_ENABLE`` IOCTL, before the EC will send them.
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Only one notifier can be registered per target category and client instance. If
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a notifier has already been registered, this IOCTL will fail with ``-EEXIST``.
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Notifiers will automatically be removed when the device file instance is
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closed.
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``SSAM_CDEV_NOTIF_UNREGISTER``
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------------------------------
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Defined as ``_IOW(0xA5, 3, struct ssam_cdev_notifier_desc)``.
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Unregisters the notifier associated with the specified target category. The
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priority field will be ignored by this IOCTL. If no notifier has been
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registered for this client instance and the given category, this IOCTL will
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fail with ``-ENOENT``.
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``SSAM_CDEV_EVENT_ENABLE``
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--------------------------
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Defined as ``_IOW(0xA5, 4, struct ssam_cdev_event_desc)``.
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Enable the event associated with the given event descriptor.
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Note that this call will not register a notifier itself, it will only enable
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events on the controller. If you want to receive events by reading from the
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device file, you will need to register the corresponding notifier(s) on that
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instance.
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Events are not automatically disabled when the device file is closed. This must
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be done manually, via a call to the ``SSAM_CDEV_EVENT_DISABLE`` IOCTL.
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``SSAM_CDEV_EVENT_DISABLE``
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---------------------------
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Defined as ``_IOW(0xA5, 5, struct ssam_cdev_event_desc)``.
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Disable the event associated with the given event descriptor.
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Note that this will not unregister any notifiers. Events may still be received
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and forwarded to user-space after this call. The only safe way of stopping
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events from being received is unregistering all previously registered
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notifiers.
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Structures and Enums
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====================
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.. kernel-doc:: include/uapi/linux/surface_aggregator/cdev.h
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