1.. SPDX-License-Identifier: GPL-2.0+ 2 3.. |ssam_cdev_request| replace:: :c:type:`struct ssam_cdev_request <ssam_cdev_request>` 4.. |ssam_cdev_request_flags| replace:: :c:type:`enum ssam_cdev_request_flags <ssam_cdev_request_flags>` 5.. |ssam_cdev_event| replace:: :c:type:`struct ssam_cdev_event <ssam_cdev_event>` 6 7============================== 8User-Space EC Interface (cdev) 9============================== 10 11The ``surface_aggregator_cdev`` module provides a misc-device for the SSAM 12controller to allow for a (more or less) direct connection from user-space to 13the SAM EC. It is intended to be used for development and debugging, and 14therefore should not be used or relied upon in any other way. Note that this 15module is not loaded automatically, but instead must be loaded manually. 16 17The provided interface is accessible through the ``/dev/surface/aggregator`` 18device-file. All functionality of this interface is provided via IOCTLs. 19These IOCTLs and their respective input/output parameter structs are defined in 20``include/uapi/linux/surface_aggregator/cdev.h``. 21 22A small python library and scripts for accessing this interface can be found 23at https://github.com/linux-surface/surface-aggregator-module/tree/master/scripts/ssam. 24 25.. contents:: 26 27 28Receiving Events 29================ 30 31Events can be received by reading from the device-file. The are represented by 32the |ssam_cdev_event| datatype. 33 34Before events are available to be read, however, the desired notifiers must be 35registered via the ``SSAM_CDEV_NOTIF_REGISTER`` IOCTL. Notifiers are, in 36essence, callbacks, called when the EC sends an event. They are, in this 37interface, associated with a specific target category and device-file-instance. 38They forward any event of this category to the buffer of the corresponding 39instance, from which it can then be read. 40 41Notifiers themselves do not enable events on the EC. Thus, it may additionally 42be necessary to enable events via the ``SSAM_CDEV_EVENT_ENABLE`` IOCTL. While 43notifiers work per-client (i.e. per-device-file-instance), events are enabled 44globally, for the EC and all of its clients (regardless of userspace or 45non-userspace). The ``SSAM_CDEV_EVENT_ENABLE`` and ``SSAM_CDEV_EVENT_DISABLE`` 46IOCTLs take care of reference counting the events, such that an event is 47enabled as long as there is a client that has requested it. 48 49Note that enabled events are not automatically disabled once the client 50instance is closed. Therefore any client process (or group of processes) should 51balance their event enable calls with the corresponding event disable calls. It 52is, however, perfectly valid to enable and disable events on different client 53instances. For example, it is valid to set up notifiers and read events on 54client instance ``A``, enable those events on instance ``B`` (note that these 55will also be received by A since events are enabled/disabled globally), and 56after no more events are desired, disable the previously enabled events via 57instance ``C``. 58 59 60Controller IOCTLs 61================= 62 63The following IOCTLs are provided: 64 65.. flat-table:: Controller IOCTLs 66 :widths: 1 1 1 1 4 67 :header-rows: 1 68 69 * - Type 70 - Number 71 - Direction 72 - Name 73 - Description 74 75 * - ``0xA5`` 76 - ``1`` 77 - ``WR`` 78 - ``REQUEST`` 79 - Perform synchronous SAM request. 80 81 * - ``0xA5`` 82 - ``2`` 83 - ``W`` 84 - ``NOTIF_REGISTER`` 85 - Register event notifier. 86 87 * - ``0xA5`` 88 - ``3`` 89 - ``W`` 90 - ``NOTIF_UNREGISTER`` 91 - Unregister event notifier. 92 93 * - ``0xA5`` 94 - ``4`` 95 - ``W`` 96 - ``EVENT_ENABLE`` 97 - Enable event source. 98 99 * - ``0xA5`` 100 - ``5`` 101 - ``W`` 102 - ``EVENT_DISABLE`` 103 - Disable event source. 104 105 106``SSAM_CDEV_REQUEST`` 107--------------------- 108 109Defined as ``_IOWR(0xA5, 1, struct ssam_cdev_request)``. 110 111Executes a synchronous SAM request. The request specification is passed in 112as argument of type |ssam_cdev_request|, which is then written to/modified 113by the IOCTL to return status and result of the request. 114 115Request payload data must be allocated separately and is passed in via the 116``payload.data`` and ``payload.length`` members. If a response is required, 117the response buffer must be allocated by the caller and passed in via the 118``response.data`` member. The ``response.length`` member must be set to the 119capacity of this buffer, or if no response is required, zero. Upon 120completion of the request, the call will write the response to the response 121buffer (if its capacity allows it) and overwrite the length field with the 122actual size of the response, in bytes. 123 124Additionally, if the request has a response, this must be indicated via the 125request flags, as is done with in-kernel requests. Request flags can be set 126via the ``flags`` member and the values correspond to the values found in 127|ssam_cdev_request_flags|. 128 129Finally, the status of the request itself is returned in the ``status`` 130member (a negative errno value indicating failure). Note that failure 131indication of the IOCTL is separated from failure indication of the request: 132The IOCTL returns a negative status code if anything failed during setup of 133the request (``-EFAULT``) or if the provided argument or any of its fields 134are invalid (``-EINVAL``). In this case, the status value of the request 135argument may be set, providing more detail on what went wrong (e.g. 136``-ENOMEM`` for out-of-memory), but this value may also be zero. The IOCTL 137will return with a zero status code in case the request has been set up, 138submitted, and completed (i.e. handed back to user-space) successfully from 139inside the IOCTL, but the request ``status`` member may still be negative in 140case the actual execution of the request failed after it has been submitted. 141 142A full definition of the argument struct is provided below. 143 144``SSAM_CDEV_NOTIF_REGISTER`` 145---------------------------- 146 147Defined as ``_IOW(0xA5, 2, struct ssam_cdev_notifier_desc)``. 148 149Register a notifier for the event target category specified in the given 150notifier description with the specified priority. Notifiers registration is 151required to receive events, but does not enable events themselves. After a 152notifier for a specific target category has been registered, all events of that 153category will be forwarded to the userspace client and can then be read from 154the device file instance. Note that events may have to be enabled, e.g. via the 155``SSAM_CDEV_EVENT_ENABLE`` IOCTL, before the EC will send them. 156 157Only one notifier can be registered per target category and client instance. If 158a notifier has already been registered, this IOCTL will fail with ``-EEXIST``. 159 160Notifiers will automatically be removed when the device file instance is 161closed. 162 163``SSAM_CDEV_NOTIF_UNREGISTER`` 164------------------------------ 165 166Defined as ``_IOW(0xA5, 3, struct ssam_cdev_notifier_desc)``. 167 168Unregisters the notifier associated with the specified target category. The 169priority field will be ignored by this IOCTL. If no notifier has been 170registered for this client instance and the given category, this IOCTL will 171fail with ``-ENOENT``. 172 173``SSAM_CDEV_EVENT_ENABLE`` 174-------------------------- 175 176Defined as ``_IOW(0xA5, 4, struct ssam_cdev_event_desc)``. 177 178Enable the event associated with the given event descriptor. 179 180Note that this call will not register a notifier itself, it will only enable 181events on the controller. If you want to receive events by reading from the 182device file, you will need to register the corresponding notifier(s) on that 183instance. 184 185Events are not automatically disabled when the device file is closed. This must 186be done manually, via a call to the ``SSAM_CDEV_EVENT_DISABLE`` IOCTL. 187 188``SSAM_CDEV_EVENT_DISABLE`` 189--------------------------- 190 191Defined as ``_IOW(0xA5, 5, struct ssam_cdev_event_desc)``. 192 193Disable the event associated with the given event descriptor. 194 195Note that this will not unregister any notifiers. Events may still be received 196and forwarded to user-space after this call. The only safe way of stopping 197events from being received is unregistering all previously registered 198notifiers. 199 200 201Structures and Enums 202==================== 203 204.. kernel-doc:: include/uapi/linux/surface_aggregator/cdev.h 205