[libcamera-devel] [PATCH v4 1/8] libcamera: delayed_controls: Add helper for controls that applies with a delay
Niklas Söderlund
niklas.soderlund at ragnatech.se
Fri Jan 8 16:21:17 CET 2021
Hi Naushir,
Thanks for your comments.
On 2020-12-15 13:53:12 +0000, Naushir Patuck wrote:
> Hi Niklas,
>
> Thank you for your patch.
>
> On Tue, 15 Dec 2020 at 00:48, Niklas Söderlund <
> niklas.soderlund at ragnatech.se> wrote:
>
> > Some sensor controls take effect with a delay as the sensor needs time
> > to adjust, for example exposure. Add an optional helper DelayedControls
> > to help pipelines deal with such controls.
> >
> > The idea is to provide a queue of controls towards the V4L2 device and
> > apply individual controls with the specified delay with the aim to get
> > predictable and retrievable control values for any given frame. To do
> > this the queue of controls needs to be at least as deep as the control
> > with the largest delay.
> >
> > The DelayedControls needs to be informed of every start of exposure.
> > This can be emulated but the helper is designed to be used with this
> > event being provide by the kernel thru V4L2 events.
> >
> > This helper is based on StaggeredCtrl from the Raspberry Pi pipeline
> > handler but expands on its API. This helpers aims to replace the
> > Raspberry Pi implementations and mimics it behavior perfectly.
> >
> > Signed-off-by: Niklas Söderlund <niklas.soderlund at ragnatech.se>
> > ---
> > * Changes since v2
> > - Drop optional argument to reset().
> > - Update commit message.
> > - Remove usage of Mutex.
> > - Rename frameStart() to applyControls)_.
> > - Rename ControlInfo to Into.
> > - Rename ControlArray to ControlRingBuffer.
> > - Drop ControlsDelays and ControlsValues.
> > - Sort headers.
> > - Rename iterators.
> > - Simplify queueCount_ handeling in reset().
> > - Add more warnings.
> > - Update documentation.
> >
> > * Changes since v2
> > - Improve error logic in queue() as suggested by Jean-Michel Hautbois.
> > - s/fistSequence_/firstSequence_/
> >
> > * Changes since v1
> > - Correct copyright to reflect work is derived from Raspberry Pi
> > pipeline handler. This was always the intention and was wrong in v1.
> > - Rewrite large parts of the documentation.
> > - Join two loops to one in DelayedControls::DelayedControls()
> > ---
> > include/libcamera/internal/delayed_controls.h | 82 ++++++
> > src/libcamera/delayed_controls.cpp | 252 ++++++++++++++++++
> > src/libcamera/meson.build | 1 +
> > 3 files changed, 335 insertions(+)
> > create mode 100644 include/libcamera/internal/delayed_controls.h
> > create mode 100644 src/libcamera/delayed_controls.cpp
> >
> > diff --git a/include/libcamera/internal/delayed_controls.h
> > b/include/libcamera/internal/delayed_controls.h
> > new file mode 100644
> > index 0000000000000000..1292b484ec9f53e9
> > --- /dev/null
> > +++ b/include/libcamera/internal/delayed_controls.h
> > @@ -0,0 +1,82 @@
> > +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> > +/*
> > + * Copyright (C) 2020, Raspberry Pi (Trading) Ltd.
> > + *
> > + * delayed_controls.h - Helper to deal with controls that are applied
> > with a delay
> > + */
> > +#ifndef __LIBCAMERA_INTERNAL_DELAYED_CONTROLS_H__
> > +#define __LIBCAMERA_INTERNAL_DELAYED_CONTROLS_H__
> > +
> > +#include <stdint.h>
> > +#include <unordered_map>
> > +
> > +#include <libcamera/controls.h>
> > +
> > +namespace libcamera {
> > +
> > +class V4L2Device;
> > +
> > +class DelayedControls
> > +{
> > +public:
> > + DelayedControls(V4L2Device *device,
> > + const std::unordered_map<uint32_t, unsigned int>
> > &delays);
> > +
> > + void reset();
> > +
> > + bool push(const ControlList &controls);
> > + ControlList get(uint32_t sequence);
> > +
> > + void applyControls(uint32_t sequence);
> > +
> > +private:
> > + class Info
> > + {
> > + public:
> > + Info()
> > + : updated(false)
> > + {
> > + }
> > +
> > + Info(const ControlValue &v)
> > + : value(v), updated(true)
> > + {
> > + }
> > +
> > + ControlValue value;
> > + bool updated;
> > + };
> > +
> > + /* \todo: Make the listSize configurable at instance creation
> > time. */
> > + static constexpr int listSize = 16;
> > + class ControlRingBuffer : public std::array<Info, listSize>
> > + {
> > + public:
> > + Info &operator[](unsigned int index)
> > + {
> > + return std::array<Info,
> > listSize>::operator[](index % listSize);
> > + }
> > +
> > + const Info &operator[](unsigned int index) const
> > + {
> > + return std::array<Info,
> > listSize>::operator[](index % listSize);
> > + }
> > + };
> > +
> > + bool queue(const ControlList &controls);
> > +
> > + V4L2Device *device_;
> > + std::unordered_map<const ControlId *, unsigned int> delays_;
> > + unsigned int maxDelay_;
> > +
> > + bool running_;
> > + uint32_t firstSequence_;
> > +
> > + uint32_t queueCount_;
> > + uint32_t writeCount_;
> > + std::unordered_map<const ControlId *, ControlRingBuffer> values_;
> > +};
> >
>
> StaggeredCtrl has a mutex to protect access to state. I wasn't entirely
> sure that was needed. Presumably the SoF event calling applyControls() and
> all other public method access occur in the same thread context, so no
> protection is needed? Do you foresee this ever changing?
As Laurent already replied, the mutex is not needed in out current
design.
>
> +
> > +} /* namespace libcamera */
> > +
> > +#endif /* __LIBCAMERA_INTERNAL_DELAYED_CONTROLS_H__ */
> > diff --git a/src/libcamera/delayed_controls.cpp
> > b/src/libcamera/delayed_controls.cpp
> > new file mode 100644
> > index 0000000000000000..db2e51f8c93c4755
> > --- /dev/null
> > +++ b/src/libcamera/delayed_controls.cpp
> > @@ -0,0 +1,252 @@
> > +/* SPDX-License-Identifier: LGPL-2.1-or-later */
> > +/*
> > + * Copyright (C) 2020, Raspberry Pi (Trading) Ltd.
> > + *
> > + * delayed_controls.h - Helper to deal with controls that are applied
> > with a delay
> > + */
> > +
> > +#include "libcamera/internal/delayed_controls.h"
> > +
> > +#include <libcamera/controls.h>
> > +
> > +#include "libcamera/internal/log.h"
> > +#include "libcamera/internal/v4l2_device.h"
> > +
> > +/**
> > + * \file delayed_controls.h
> > + * \brief Helper to deal with controls that are applied with a delay
> > + */
> > +
> > +namespace libcamera {
> > +
> > +LOG_DEFINE_CATEGORY(DelayedControls)
> > +
> > +/**
> > + * \class DelayedControls
> > + * \brief Helper to deal with controls that take effect with a delay
> > + *
> > + * Some sensor controls take effect with a delay as the sensor needs time
> > to
> > + * adjust, for example exposure and focus. This is a helper class to deal
> > with
> > + * such controls and the intended users are pipeline handlers.
> > + *
> > + * The idea is to extend the concept of the buffer depth of a pipeline the
> > + * application needs to maintain to also cover controls. Just as with
> > buffer
> > + * depth if the application keeps the number of requests queued above the
> > + * control depth the controls are guaranteed to take effect for the
> > correct
> > + * request. The control depth is determined by the control with the
> > greatest
> > + * delay.
> > + */
> > +
> > +/**
> > + * \brief Construct a DelayedControls instance
> > + * \param[in] device The V4L2 device the controls have to be applied to
> > + * \param[in] delays Map of the numerical V4L2 control ids to their
> > associated
> > + * delays (in frames)
> > + *
> > + * Only controls specified in \a delays are handled. If it's desired to
> > mix
> > + * delayed controls and controls that take effect immediately the
> > immediate
> > + * controls must be listed in the \a delays map with a delay value of 0.
> > + */
> > +DelayedControls::DelayedControls(V4L2Device *device,
> > + const std::unordered_map<uint32_t,
> > unsigned int> &delays)
> > + : device_(device), maxDelay_(0)
> > +{
> > + const ControlInfoMap &controls = device_->controls();
> > +
> > + /*
> > + * Create a map of control ids to delays for controls exposed by
> > the
> > + * device.
> > + */
> > + for (auto const &delay : delays) {
> > + auto it = controls.find(delay.first);
> > + if (it == controls.end()) {
> > + LOG(DelayedControls, Error)
> > + << "Delay request for control id "
> > + << utils::hex(delay.first)
> > + << " but control is not exposed by device "
> > + << device_->deviceNode();
> > + continue;
> > + }
> > +
> > + const ControlId *id = it->first;
> > +
> > + delays_[id] = delay.second;
> > +
> > + LOG(DelayedControls, Debug)
> > + << "Set a delay of " << delays_[id]
> > + << " for " << id->name();
> > +
> > + maxDelay_ = std::max(maxDelay_, delays_[id]);
> > + }
> > +
> > + reset();
> > +}
> > +
> > +/**
> > + * \brief Reset state machine
> > + *
> > + * Resets the state machine to a starting position based on control values
> > + * retrieved from the device.
> > + */
> > +void DelayedControls::reset()
> > +{
> > + running_ = false;
> > + firstSequence_ = 0;
> > + queueCount_ = 1;
> > + writeCount_ = 0;
> > +
> > + /* Retrieve control as reported by the device. */
> > + std::vector<uint32_t> ids;
> > + for (auto const &delay : delays_)
> > + ids.push_back(delay.first->id());
> > +
> > + ControlList controls = device_->getControls(ids);
> > +
> > + /* Seed the control queue with the controls reported by the
> > device. */
> > + values_.clear();
> > + for (const auto &ctrl : controls) {
> > + const ControlId *id =
> > device_->controls().idmap().at(ctrl.first);
> > + values_[id][0] = Info(ctrl.second);
> > + }
> >
>
> I think this may have been mentioned in one of the earlier rounds - this
> may not be correct as all the controls available to the device may not be
> registered with DelayedControls. In those cases, the values_ map lookup
> would fail. You would need to validate that id is an available key in the
> map.
Is this not already done? The 'controls' that are iterated in this loop
is constructed from the IDs in delays_ which only contains the controls
with an associated delay.
>
>
> > +}
> > +
> > +/**
> > + * \brief Push a set of controls on the queue
> > + * \param[in] controls List of controls to add to the device queue
> > + *
> > + * Push a set of controls to the control queue. This increases the
> > control queue
> > + * depth by one.
> > + *
> > + * \returns true if \a controls are accepted, or false otherwise
> > + */
> > +bool DelayedControls::push(const ControlList &controls)
> > +{
> > + return queue(controls);
> > +}
> >
>
> Apologies, I may have missed something obvious, but why do we have the
> push() and queue() methods when one calls the other?
Good call! This is a leftover from when there was a mutex that needed to
be locked when called from the public API but not when the functionality
was used internally where the mutex was already locked. Will fold these
two together.
>
>
> > +
> > +bool DelayedControls::queue(const ControlList &controls)
> > +{
> > + /* Copy state from previous frame. */
> > + for (auto &ctrl : values_) {
> > + Info &info = ctrl.second[queueCount_];
> > + info.value = values_[ctrl.first][queueCount_ - 1].value;
> > + info.updated = false;
> > + }
> > +
> > + /* Update with new controls. */
> > + const ControlIdMap &idmap = device_->controls().idmap();
> > + for (const auto &control : controls) {
> > + const auto &it = idmap.find(control.first);
> > + if (it == idmap.end()) {
> > + LOG(DelayedControls, Warning)
> > + << "Unknown control " << control.first;
> > + return false;
> > + }
> > +
> > + const ControlId *id = it->second;
> > +
> > + if (delays_.find(id) == delays_.end())
> > + return false;
> > +
> > + Info &info = values_[id][queueCount_];
> > +
> > + info.value = control.second;
> > + info.updated = true;
> > +
> > + LOG(DelayedControls, Debug)
> > + << "Queuing " << id->name()
> > + << " to " << info.value.toString()
> > + << " at index " << queueCount_;
> > + }
> > +
> > + queueCount_++;
> > +
> > + return true;
> > +}
> > +
> > +/**
> > + * \brief Read back controls in effect at a sequence number
> > + * \param[in] sequence The sequence number to get controls for
> > + *
> > + * Read back what controls where in effect at a specific sequence number.
> > The
> > + * history is a ring buffer of 16 entries where new and old values
> > coexist. It's
> > + * the callers responsibility to not read too old sequence numbers that
> > have been
> > + * pushed out of the history.
> > + *
> > + * Historic values are evicted by pushing new values onto the queue using
> > + * push(). The max history from the current sequence number that yields
> > valid
> > + * values are thus 16 minus number of controls pushed.
> > + *
> > + * \return The controls at \a sequence number
> > + */
> > +ControlList DelayedControls::get(uint32_t sequence)
> > +{
> > + uint32_t adjustedSeq = sequence - firstSequence_ + 1;
> > + unsigned int index = std::max<int>(0, adjustedSeq - maxDelay_);
> > +
> > + ControlList out(device_->controls());
> > + for (const auto &ctrl : values_) {
> > + const ControlId *id = ctrl.first;
> > + const Info &info = ctrl.second[index];
> > +
> > + out.set(id->id(), info.value);
> > +
> > + LOG(DelayedControls, Debug)
> > + << "Reading " << id->name()
> > + << " to " << info.value.toString()
> > + << " at index " << index;
> > + }
> > +
> > + return out;
> > +}
> > +
> > +/**
> > + * \brief Inform DelayedControls of the start of a new frame
> > + * \param[in] sequence Sequence number of the frame that started
> > + *
> > + * Inform the state machine that a new frame has started and of its
> > sequence
> > + * number. Any user of these helpers is responsible to inform the helper
> > about
> > + * the start of any frame.This can be connected with ease to the start of
> > a
> > + * exposure (SOE) V4L2 event.
> > + */
> > +void DelayedControls::applyControls(uint32_t sequence)
> > +{
> > + LOG(DelayedControls, Debug) << "frame " << sequence << " started";
> > +
> > + if (!running_) {
> > + firstSequence_ = sequence;
> > + running_ = true;
> > + }
> > +
> > + /*
> > + * Create control list peaking ahead in the value queue to ensure
> > + * values are set in time to satisfy the sensor delay.
> > + */
> > + ControlList out(device_->controls());
> > + for (const auto &ctrl : values_) {
> > + const ControlId *id = ctrl.first;
> > + unsigned int delayDiff = maxDelay_ - delays_[id];
> > + unsigned int index = std::max<int>(0, writeCount_ -
> > delayDiff);
> > + const Info &info = ctrl.second[index];
> > +
> > + if (info.updated) {
> > + out.set(id->id(), info.value);
> > + LOG(DelayedControls, Debug)
> > + << "Setting " << id->name()
> > + << " to " << info.value.toString()
> > + << " at index " << index;
> > + }
> > + }
> > +
> > + writeCount_++;
> > +
> > + while (writeCount_ >= queueCount_) {
> > + LOG(DelayedControls, Debug)
> > + << "Queue is empty, auto queue no-op.";
> > + queue({});
> > + }
> > +
> > + device_->setControls(&out);
> >
>
> As mentioned previously, this will need to separate out controls that must
> be written immediately (e.g. VBLANK) instead of batched together, but that
> can be added at a later stage.
I agree this is just the first step and I'm sure we need to evolve and
rework parts of DelayedControls as we gain more capabilities.
>
> Regards,
> Naush
>
>
>
> > +}
> > +
> > +} /* namespace libcamera */
> > diff --git a/src/libcamera/meson.build b/src/libcamera/meson.build
> > index 387d5d88ecae11ad..5a4bf0d7ba4fd231 100644
> > --- a/src/libcamera/meson.build
> > +++ b/src/libcamera/meson.build
> > @@ -12,6 +12,7 @@ libcamera_sources = files([
> > 'controls.cpp',
> > 'control_serializer.cpp',
> > 'control_validator.cpp',
> > + 'delayed_controls.cpp',
> > 'device_enumerator.cpp',
> > 'device_enumerator_sysfs.cpp',
> > 'event_dispatcher.cpp',
> > --
> > 2.29.2
> >
> >
--
Regards,
Niklas Söderlund
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