From patchwork Wed Nov 11 10:20:14 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Paul Elder X-Patchwork-Id: 10409 Return-Path: X-Original-To: parsemail@patchwork.libcamera.org Delivered-To: parsemail@patchwork.libcamera.org Received: from lancelot.ideasonboard.com (lancelot.ideasonboard.com [92.243.16.209]) by patchwork.libcamera.org (Postfix) with ESMTPS id 85242BDB89 for ; Wed, 11 Nov 2020 10:20:24 +0000 (UTC) Received: from lancelot.ideasonboard.com (localhost [IPv6:::1]) by lancelot.ideasonboard.com (Postfix) with ESMTP id 09B5D630BE; Wed, 11 Nov 2020 11:20:24 +0100 (CET) Authentication-Results: lancelot.ideasonboard.com; dkim=fail reason="signature verification failed" (1024-bit key; unprotected) header.d=ideasonboard.com header.i=@ideasonboard.com header.b="Qgdr/KgM"; dkim-atps=neutral Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [IPv6:2001:4b98:dc2:55:216:3eff:fef7:d647]) by lancelot.ideasonboard.com (Postfix) with ESMTPS id 8B9806033F for ; Wed, 11 Nov 2020 11:20:22 +0100 (CET) Received: from pyrite.rasen.tech (unknown [IPv6:2400:4051:61:600:2c71:1b79:d06d:5032]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 3E8CFA19 for ; Wed, 11 Nov 2020 11:20:20 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1605090022; bh=GR4GS9P2NvhFx/ObXUBi7Bd8uSphioDcsdrjgmb/T6I=; h=Date:From:To:Subject:References:In-Reply-To:From; b=Qgdr/KgMTD60Z3LuqyjFIZ1dPPutEe4Tj7h85/+HT/hOhCEkyGLkkKh1rtl+n6ymc ycJkOQAQWnHvPS7JHdp/1WEvZE+C+XS+Yxy2Ax4uPy0ljVrXCyuAApO3O3o0UUVdfI 5JaEsLROwJOyC8EhaJGjKa+n9j1cHhPhKNDdU4o4= Date: Wed, 11 Nov 2020 19:20:14 +0900 From: paul.elder@ideasonboard.com To: libcamera-devel@lists.libcamera.org Message-ID: <20201111102014.GA1811@pyrite.rasen.tech> References: <20201106103707.49660-1-paul.elder@ideasonboard.com> <20201106103707.49660-37-paul.elder@ideasonboard.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20201106103707.49660-37-paul.elder@ideasonboard.com> Subject: [libcamera-devel] [PATCH v4.1 36/37] Documentation: Add IPA writers guide X-BeenThere: libcamera-devel@lists.libcamera.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: libcamera-devel-bounces@lists.libcamera.org Sender: "libcamera-devel" Add a guide about writing IPAs. Signed-off-by: Paul Elder --- Changes in v4.1: - Add section on namespacing, custom data structures, compiling, and usage of the data structures and interface - Add examples to the main ipa interface and event ipa interface sections New in v4 --- Documentation/guides/ipa.rst | 456 +++++++++++++++++++++++++++++++++++ Documentation/index.rst | 1 + Documentation/meson.build | 1 + 3 files changed, 458 insertions(+) create mode 100644 Documentation/guides/ipa.rst diff --git a/Documentation/guides/ipa.rst b/Documentation/guides/ipa.rst new file mode 100644 index 00000000..575f3ca1 --- /dev/null +++ b/Documentation/guides/ipa.rst @@ -0,0 +1,456 @@ +.. SPDX-License-Identifier: CC-BY-SA-4.0 + +IPA Writers Guide +================= + +IPA are Image Processing Algorithm modules. They provide functionality that +the pipeline handler can use for image processing. + +This guide so far only covers definition the IPA interface, and how to plumb +the connection between the pipeline handler and the IPA. + +The IPA interface and protocol +------------------------------ + +The IPA interface defines the interface between the pipeline handler and the +IPA. Specifically, it defines the functions that the IPA exposes that the +pipeline handler can call, and the Signals that the pipeline handler can +connect to to receive data from the IPA asyncrhonously. In addition, it +contains any custom data structures that the pipeline handler and IPA may +pass to each other. + +The IPA protocol refers to the agreement between the pipeline handler and the +IPA regarding the expected response(s) from the IPA for given calls to the IPA. +This protocol doesn't need to be declared anywhere in code, but it would be +useful to document it, as there may be many different IPAs for one pipeline +handler. + +The IPA interface must be defined in a mojom file. The interface includes: +- the functions that the pipeline handler can call from the IPA +- Signals in the pipeline handler that the IPA can emit +- any data structures that are to be passed between the pipeline handler and + the IPA +All IPA of a given pipeline handler use the same IPA interface. The IPA +interface definition is thus likely to be written by the pipeline handler +author, based on how they imagine the pipeline handler will interact with +the IPA. + +The entire IPA interface, including the functions, Signals, and any custom +structs shall be defined in in a file named {pipeline_name}.mojom under +include/libcamera/ipa/ using the mojo interface definition language (IDL). This +will be covered in detail in the following sections. + +Namespacing +----------- + +It is recommended to use namespacing, to avoid potential collisions with +libcamera types. Use mojo's module directive for this. + +It must be the first meaningful line in the mojo data definition file, for +example (defining a raspberry pi IPA): + +.. code-block:: C++ + module ipa.rpi; + +This will become the ipa::rpi namespace in C++ code. + +Data containers +--------------- + +Since the data passed between the pipeline handler and the IPA must support +serialization, any custom data containers must be defined with the mojo IDL. + +The following list of libcamera objects are supported in the interface +definition, and may be used as function parameter types or struct field types: + +- CameraSensorInfo +- ControlInfoMap +- ControlList +- FileDescriptor +- IPABuffer +- IPASettings +- IPAStream + +To use them, core.mojom must be included in the mojo data definition file: + +.. code-block:: C++ + import "include/libcamera/ipa/core.mojom"; + +Other custom structs may be defined and used as well. There is no requirement +that they must be defined before usage. enums and structs are supported. + +The following is an example of a definition of an enum, for the purpose of +being used as flags: + +.. code-block:: C++ + enum ConfigParameters { + RPI_IPA_CONFIG_LS_TABLE = 0x01, + RPI_IPA_CONFIG_STAGGERED_WRITE = 0x02, + RPI_IPA_CONFIG_SENSOR = 0x04, + RPI_IPA_CONFIG_DROP_FRAMES = 0x08, + }; + +The following is an example of a definition of a struct: + +.. code-block:: C++ + struct ConfigInput { + uint32 op; + uint32 transform; + FileDescriptor lsTableHandle; + int32 lsTableHandleStatic = -1; + map streamConfig; + array buffers; + }; + +This example has some special things about it. First of all, it uses the +FileDescriptor data type. This type must be used to ensure that the file +descriptor that it contains is translated property across the IPC boundary +(when the IPA is in an isolated process). + +This does mean that if the file descriptor should be sent without being +translated (for example, for the IPA to tell the pipeline handler which +fd *that the pipeline handler holds* to act on), then it must be in a +regular int32 type. + +This example also illustrates that struct fields may have default values, as +is assigned to lsTableHandleStatic. This is the value that the field will +take when the struct is constructed with the default constructor. + +Arrays and maps are supported as well. They are translated to C++ vectors and +maps, respectively. The members of the arrays and maps are embedded, and cannot +be const. + +Note that nullable fields, static-length arrays, handles, and unions, which +are supported by mojo, are not supported by our code generator. + +TODO what about versioning, and numbered fields? + +The Main IPA interface +---------------------- + +The IPA interface is split in two parts, the Main IPA interface, which +describes the functions that the pipeline handler can call from the IPA, +and the Event IPA interface, which describes the Signals in the pipeline +handler that the IPA can emit. Both must be defined. This section focuses +on the Main IPA interface. + +The main interface must be named as IPA{pipeline_name}Interface. + +At minimum, the following three functions must be present (and implemented): +- init(IPASettings settings) => (int32 ret); +- start() => (int32 ret); +- stop(); + +All three of these functions are synchronous. + +All input parameters will become const references, except for arithmetic types, +which will be passed by value. Output parameters will become pointers, unless +there is only one primitive output parameter, in which case it will become a +a regular return value. + +const is not allowed inside of arrays and maps. mojo arrays will become C++ +std::vector<>. + +By default, all methods defined in the main interface are synchronous. This +means that in the case of IPC (ie. isolated IPA), the function call will not +return until the return value or output parameters are ready. To specify an +asynchronous function, the [async] attribute can be used. Asynchronous +methods must not have any return value or output parameters, since in the +case of IPC the call needs to return immediately. + +It is also possible that the IPA will not be run in isolation. In this case, +the IPA thread will not exist until start() is called. This means that in the +case of no isolation, asynchronous calls cannot be made before start(). Since +the IPA interface must be the same regardless of isolation, the same +restriction applies to the case of isolation, and any function that will be +called before start() must be synchronous. + +In addition, any call made after start() and before stop() must be +asynchronous. The motivation for this is to avoid damaging real time +performance of the pipeline handler. If the pipeline handler wants some data +from the IPA, the IPA should return the data asynchronously via an event +(see "The Event IPA interface"). + +In addition the following must be defined in {pipeline_name}.h in the +libcamera namespace: + +.. code-block:: C++ + static ControlInfoMap {pipeline_name}::controls; + +It may be empty. This will be the default ControlInfoMap used when +serializing and deserializing any ControlLists if it is not specified +in the ControlList. + +The following is an example of a main interface definition: + +.. code-block:: C++ + interface IPARPiInterface { + init(IPASettings settings) => (int32 ret); + start() => (int32 ret); + stop(); + + configure(CameraSensorInfo sensorInfo, + map streamConfig, + map entityControls, + ConfigInput ipaConfig) + => (ConfigOutput results); + + mapBuffers(array buffers); + unmapBuffers(array ids); + + [async] signalStatReady(uint32 bufferId); + [async] signalQueueRequest(ControlList controls); + [async] signalIspPrepare(IspPreparePayload data); + }; + + +The first three functions are the required functions. Functions do not need to +have return values, like stop(), mapBuffers(), and unmapBuffers(). In the case +of asynchronous functions, as explained before, they *must not* have return +values. + +The Event IPA interface +----------------------- + +The event IPA interface describes the Signals in the pipeline handler that the +IPA can emit. It must be defined. If there are no event functions, then it may +be empty. These emissions are meant to notify the pipeline handler of some +event, such as reqeust data is ready, and *must not* be used to drive the +camera pipeline from the IPA. + +The event interface must be named as IPA{pipeline_name}EventInterface. + +Methods defined in the event interface are implictly asynchronous. +They thus cannot return any value. Specifying the [async] tag is not +necessary. + +Methods defined in the event interface will become Signals in the IPA +interface. The IPA can emit signals, while the pipeline handler can connect +slots to them. + +The following is an example of an event interface definition: + +.. code-block:: C++ + interface IPARPiEventInterface { + statsMetadataComplete(uint32 bufferId, ControlList controls); + runIsp(uint32 bufferId); + embeddedComplete(uint32 bufferId); + setIsp(ControlList controls); + setStaggered(ControlList controls); + }; + +Compiling the IPA interface +--------------------------- + +After the IPA interface is defined in include/libcamera/ipa/{pipeline_name}.mojom, +and entry for it must be added in meson so that it can be compiled. The filename +must be added to the ipa_mojom_files object in include/libcamera/ipa/meson.build. + +For example, adding the raspberrypi.mojom file to meson: + +.. code-block:: meson + ipa_mojom_files = [ + 'raspberrypi.mojom', + ] + +This will cause the mojo data definition file to be compiled. Specifically, it +generated five files: +- a header describing the custom data structures, and the complete IPA interface +- a serializer implementing de/serialization for the custom data structures +- a proxy header describing a specialized IPA proxy +- a proxy source implementing the IPA proxy +- a proxy worker source implementing the other end of the IPA proxy + +The pipeline handler and the IPA only require the header and the proxy header. +The serializer is only used internally by the proxy. + +Using the custom data structures +-------------------------------- + +To use the custom data structures that are defined in the mojo data definition +file, the follow header must be included: + +.. code-block:: C++ + #include + +The POD types of the structs simply become their C++ counterparts, eg. uint32 +in mojo will become uint32_t in C++. mojo map becomes C++ std::map, and mojo +array becomes C++ std::vector. All members of maps and vectors are embedded, +and are not pointers. The members cannot be const. + +All fields of structs are the name as specified in the data definition file, +with an underscore at the end. For example, the following struct as defined +in the mojo file: + +.. code-block:: C++ + struct StaggeredWritePayload { + uint32 gainDelay = 1; + uint32 exposureDelay; + uint32 sensorMetadata; + }; + +Will become this in C++: + +.. code-block:: C++ + struct StaggeredWritePayload { + uint32_t gainDelay_; + uint32_t exposureDelay_; + uint32_t sensorMetadata_; + }; + +The generated structs will also have two constructors, a constructor that +fills all fields with the default values, and a second constructor that takes +a value for every field. The default value constructor will fill in the fields +with the specified default value, if it exists. In the above example, gainDelay_ +will be initialized to 1. If no default value is specified, then it will be +filled in as zero (or -1 for a FileDescriptor type). + +All fields and constructors/deconstructors in these generated structs are public. + +Using the IPA interface (pipeline handler) +----------------------------------------- + +The following headers are necessary to use an IPA in the pipeline handler +(with raspberrypi as an example): + +.. code-block:: C++ + #include + #include + +The first header includes definitions of the custom data structures, and +the definition of the complete IPA interface (including both the Main and +the Event IPA interfaces). The name of the header file is comes from the name +of the mojom file, which in this case was raspberrypi.mojom. + +The second header inclues the definition of the specialized IPA proxy. It +exposes the complete IPA interface. We will see how to use it in this section. + +In the pipeline handler, we first need to construct a specialized IPA proxy. +From the point of view of the pipeline hander, this is the object that is the +IPA. + +To do so, we invoke the IPAManager: + +.. code-block:: C++ + std::unique_ptr ipa_ = + IPAManager::createIPA(pipe_, 1, 1); + +The ipa::rpi namespace comes from the namespace that we defined in the mojo +data definition file, in the "Namespacing" section. The name of the proxy, +IPAProxyRPi, comes from the name given to the main IPA interface, +IPARPiInterface, in the "The Main IPA interface" section. + +The return value of IPAManager::createIPA shall be error-checked, to confirm +that the returned pointer is not a nullptr. + +After this, before initializing the IPA, slots should be connected to all of +the IPA's Signals, as defined in the Event IPA interface: + +.. code-block:: C++ + ipa_->statsMetadataComplete.connect(this, &RPiCameraData::statsMetadataComplete); + ipa_->runIsp.connect(this, &RPiCameraData::runIsp); + ipa_->embeddedComplete.connect(this, &RPiCameraData::embeddedComplete); + ipa_->setIsp.connect(this, &RPiCameraData::setIsp); + ipa_->setStaggered.connect(this, &RPiCameraData::setStaggered); + +The slot functions have a function signature based on the function definition +in the Event IPA interface. All plain old data (POD) types are as-is (with +their C++ versions, eg. uint32 -> uint32_t), and all structs are const references. + +For example, for the following entry in the Event IPA interface: + +.. code-block:: C++ + statsMetadataComplete(uint32 bufferId, ControlList controls); + +A function with the following function signature shall be connected to the +signal: + +.. code-block:: C++ + statsMetadataComplete(uint32_t bufferId, const ControlList &controls); + +After connecting the slots to the signals, the IPA should be initialized +(fill in settings accordingly): + +.. code-block:: C++ + IPASettings settings{}; + ipa_->init(settings); + +At this point, any IPA functions that were defined in the Main IPA interface +can be called as if they were regular member functions, for example: + +.. code-block:: C++ + ipa_->start(); + ipa_->configure(sensorInfo_, streamConfig, entityControls, ipaConfig, &result); + ipa_->signalStatReady(RPi::BufferMask::STATS | static_cast(index)); + +Remember that any functions designated as asynchronous *must not* be called +before start(). + +TODO anything special about start() and stop() ? + +Using the IPA interface (IPA) +----------------------------- + +The following header is necessary to implement an IPA (with raspberrypi as +an example): + +.. code-block:: C++ + #include + +This header includes definitions of the custom data structures, and +the definition of the complete IPA interface (including both the Main and +the Event IPA interfaces). The name of the header file is comes from the name +of the mojom file, which in this case was raspberrypi.mojom. + +The IPA must implement the IPA interface class that is defined in the header. +In the case of our example, that is ipa::rpi::IPARPiInterface. The ipa::rpi +namespace comes from the namespace that we defined in the mojo data definition +file, in the "Namespacing" section. The name of the interface is the same as +the name given to the Main IPA interface. + +The function signature rules are the same as for the slots in the pipeline +handler side; PODs are passed by value, and structs are passed by const +reference. For the Main IPA interface, output values are also allowed (only +for synchronous calls), so there may be output parameters as well. If the +output parameter is a single POD it will be returned by value, otherwise +(multiple PODs or struct(s)) it will be returned by output parameter pointers. + +For example, for the following function specification in the Main IPA interface +definition: + +.. code-block:: C++ + configure(CameraSensorInfo sensorInfo, + uint32 exampleNumber, + map streamConfig, + map entityControls, + ConfigInput ipaConfig) + => (ConfigOutput results); + +We will need to implement a function with the following function signature: + +.. code-block:: C++ + + void configure(const CameraSensorInfo &sensorInfo, + uint32_t exampleNumber, + const std::map &streamConfig, + const std::map &entityControls, + const ipa::rpi::ConfigInput &data, + ipa::rpi::ConfigOutput *response); + +The return value is void, because the output parameter is not a single POD. +Instead, it becomes an output parameter pointer. The non-POD input parameters +become const references, and the POD input parameter is passed by value. + +At any time (though usually only in response to an IPA call), the IPA may send +data to the pipeline handler by emitting signals. These signals are defined +in the C++ IPA interface class (which is in the generated and included header). + +For example, for the following function defined in the Event IPA interface: + +.. code-block:: C++ + statsMetadataComplete(uint32 bufferId, ControlList controls); + +We can emit a signal like so: + +.. code-block:: C++ + statsMetadataComplete.emit(bufferId & RPi::BufferMask::ID, libcameraMetadata_); diff --git a/Documentation/index.rst b/Documentation/index.rst index ff697d4f..8bc8922e 100644 --- a/Documentation/index.rst +++ b/Documentation/index.rst @@ -16,4 +16,5 @@ Developer Guide Application Writer's Guide Pipeline Handler Writer's Guide + IPA Writer's guide Tracing guide diff --git a/Documentation/meson.build b/Documentation/meson.build index 59107151..17f3b9d7 100644 --- a/Documentation/meson.build +++ b/Documentation/meson.build @@ -52,6 +52,7 @@ if sphinx.found() 'docs.rst', 'index.rst', 'guides/introduction.rst', + 'guides/ipa.rst', 'guides/application-developer.rst', 'guides/pipeline-handler.rst', 'guides/tracing.rst',