ipa: libipa: Introduce Algorithm class template

The algorithms are using the same function names with specialized
parameters. Instead of duplicating code, introduce a libipa Algorithm
class which implements a base class with template parameters in libipa,
and use it in each IPA.

As we now won't need an algorithm class for each IPA, move the
documentation to libipa, and make it agnostic of the IPA used. While at
it, fix the IPU3::Algorithm::Awb documentation.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Jean-Michel Hautbois <jeanmichel.hautbois@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Reviewed-by: Umang Jain <umang.jain@ideasonboard.com>

3 files changed, 134 insertions, 0 deletions

diff --git a/src/ipa/libipa/algorithm.cpp b/src/ipa/libipa/algorithm.cpp
new file mode 100644
index 00000000..398d5372
--- /dev/null
+++ b/src/ipa/libipa/algorithm.cpp
@@ -0,0 +1,95 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2021, Ideas On Board
+ *
+ * algorithm.cpp - IPA control algorithm interface
+ */
+
+#include "algorithm.h"
+
+/**
+ * \file algorithm.h
+ * \brief Algorithm common interface
+ */
+
+namespace libcamera {
+
+namespace ipa {
+
+/**
+ * \class Algorithm
+ * \brief The base class for all IPA algorithms
+ * \tparam Context The type of shared IPA context
+ * \tparam Config The type of the IPA configuration data
+ * \tparam Params The type of the ISP specific parameters
+ * \tparam Stats The type of the IPA statistics and ISP results
+ *
+ * The Algorithm class defines a standard interface for IPA algorithms. By
+ * abstracting algorithms, it makes possible the implementation of generic code
+ * to manage algorithms regardless of their specific type.
+ */
+
+/**
+ * \fn Algorithm::configure()
+ * \brief Configure the Algorithm given an IPAConfigInfo
+ * \param[in] context The shared IPA context
+ * \param[in] configInfo The IPA configuration data, received from the pipeline
+ * handler
+ *
+ * Algorithms may implement a configure operation to pre-calculate
+ * parameters prior to commencing streaming.
+ *
+ * Configuration state may be stored in the IPASessionConfiguration structure of
+ * the IPAContext.
+ *
+ * \return 0 if successful, an error code otherwise
+ */
+
+/**
+ * \fn Algorithm::prepare()
+ * \brief Fill the \a params buffer with ISP processing parameters for a frame
+ * \param[in] context The shared IPA context
+ * \param[out] params The ISP specific parameters.
+ *
+ * This function is called for every frame when the camera is running before it
+ * is processed by the ISP to prepare the ISP processing parameters for that
+ * frame.
+ *
+ * Algorithms shall fill in the parameter structure fields appropriately to
+ * configure the ISP processing blocks that they are responsible for. This
+ * includes setting fields and flags that enable those processing blocks.
+ */
+
+/**
+ * \fn Algorithm::process()
+ * \brief Process ISP statistics, and run algorithm operations
+ * \param[in] context The shared IPA context
+ * \param[in] stats The IPA statistics and ISP results
+ *
+ * This function is called while camera is running for every frame processed by
+ * the ISP, to process statistics generated from that frame by the ISP.
+ * Algorithms shall use this data to run calculations and update their state
+ * accordingly.
+ *
+ * Processing shall not take an undue amount of time, and any extended or
+ * computationally expensive calculations or operations must be handled
+ * asynchronously in a separate thread.
+ *
+ * Algorithms can store state in their respective IPAFrameContext structures,
+ * and reference state from the IPAFrameContext of other algorithms.
+ *
+ * \todo Historical data may be required as part of the processing.
+ * Either the previous frame, or the IPAFrameContext state of the frame
+ * that generated the statistics for this operation may be required for
+ * some advanced algorithms to prevent oscillations or support control
+ * loops correctly. Only a single IPAFrameContext is available currently,
+ * and so any data stored may represent the results of the previously
+ * completed operations.
+ *
+ * Care shall be taken to ensure the ordering of access to the information
+ * such that the algorithms use up to date state as required.
+ */
+
+} /* namespace ipa */
+
+} /* namespace libcamera */
diff --git a/src/ipa/libipa/algorithm.h b/src/ipa/libipa/algorithm.h
new file mode 100644
index 00000000..766aee5d
--- /dev/null
+++ b/src/ipa/libipa/algorithm.h
@@ -0,0 +1,38 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2021, Ideas On Board
+ *
+ * algorithm.h - ISP control algorithm interface
+ */
+#pragma once
+
+namespace libcamera {
+
+namespace ipa {
+
+template<typename Context, typename Config, typename Params, typename Stats>
+class Algorithm
+{
+public:
+	virtual ~Algorithm() {}
+
+	virtual int configure([[maybe_unused]] Context &context,
+			      [[maybe_unused]] const Config &configInfo)
+	{
+		return 0;
+	}
+
+	virtual void prepare([[maybe_unused]] Context &context,
+			     [[maybe_unused]] Params *params)
+	{
+	}
+
+	virtual void process([[maybe_unused]] Context &context,
+			     [[maybe_unused]] const Stats *stats)
+	{
+	}
+};
+
+} /* namespace ipa */
+
+} /* namespace libcamera */
diff --git a/src/ipa/libipa/meson.build b/src/ipa/libipa/meson.build
index 4d073a03..161cc5a1 100644
--- a/src/ipa/libipa/meson.build
+++ b/src/ipa/libipa/meson.build
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: CC0-1.0
 
 libipa_headers = files([
+    'algorithm.h',
     'camera_sensor_helper.h',
     'histogram.h'
 ])