[libcamera-devel] [PATCH v3 1/3] libcamera: v4l2_videodevice: Add a dequeue timer

[Laurent Pinchart]

Hi Naush,

On Tue, Apr 05, 2022 at 03:19:29PM +0100, Naushir Patuck wrote:
> On Tue, 5 Apr 2022 at 14:56, Umang Jain wrote:
> > On 3/29/22 16:59, Naushir Patuck via libcamera-devel wrote:
> > > Add a timer that gets reset on every buffer dequeue event. If the timeout
> > > expires, optionally call a slot in the pipeline handler to handle this
> > > condition. This may be useful in detecting and handling stalls in either the
> > > hardware or device driver.
> > >
> > > Signed-off-by: Naushir Patuck <naush at raspberrypi.com>
> > > ---
> > >   include/libcamera/internal/v4l2_videodevice.h | 10 ++++
> > >   src/libcamera/v4l2_videodevice.cpp            | 54 +++++++++++++++++++
> > >   2 files changed, 64 insertions(+)
> > >
> > > diff --git a/include/libcamera/internal/v4l2_videodevice.h b/include/libcamera/internal/v4l2_videodevice.h
> > > index cfeae7bd6c52..2a9ba1fe5c71 100644
> > > --- a/include/libcamera/internal/v4l2_videodevice.h
> > > +++ b/include/libcamera/internal/v4l2_videodevice.h
> > > @@ -9,6 +9,7 @@
> > >
> > >   #include <array>
> > >   #include <atomic>
> > > +#include <chrono>
> > >   #include <memory>
> > >   #include <optional>
> > >   #include <stdint.h>
> > > @@ -20,6 +21,7 @@
> > >   #include <libcamera/base/class.h>
> > >   #include <libcamera/base/log.h>
> > >   #include <libcamera/base/signal.h>
> > > +#include <libcamera/base/timer.h>
> > >   #include <libcamera/base/unique_fd.h>
> > >
> > >   #include <libcamera/color_space.h>
> > > @@ -217,6 +219,9 @@ public:
> > >       int streamOn();
> > >       int streamOff();
> > >
> > > +     void setDequeueTimeout(std::chrono::milliseconds msec);
> > > +     Signal<> dequeueTimeout;
> > > +
> > >       static std::unique_ptr<V4L2VideoDevice>
> > >       fromEntityName(const MediaDevice *media, const std::string &entity);
> > >
> > > @@ -253,6 +258,8 @@ private:
> > >       void bufferAvailable();
> > >       FrameBuffer *dequeueBuffer();
> > >
> > > +     void watchdogExpired();
> > > +
> > >       V4L2Capability caps_;
> > >       V4L2DeviceFormat format_;
> > >       const PixelFormatInfo *formatInfo_;
> > > @@ -266,6 +273,9 @@ private:
> > >       EventNotifier *fdBufferNotifier_;
> > >
> > >       State state_;
> > > +
> > > +     Timer watchdog_;
> > > +     std::chrono::milliseconds watchdogDuration_;
> >
> > Any particular reason this is std::chrono::miiliseconds instead of using
> > utils::Duration ?
> 
> In the previous revision, I did use the utils::Duration type for this variable.
> However, Laurent suggested that we might want to avoid that as he intends to
> move utils::Duration to the "public" API, and would not be available to use
> in this case.  So I switched to std::chrono::milliseconds.

That was about usage of utils::Duration in the libcamera-base layer
itself (in the Timer class if I recall correctly). You can use it in
here if desired, types defined in the libcamera API are accessible to
libcamera internals.

> > >   };
> > >
> > >   class V4L2M2MDevice
> > > diff --git a/src/libcamera/v4l2_videodevice.cpp b/src/libcamera/v4l2_videodevice.cpp
> > > index 009f6d55610f..22191cb9de4d 100644
> > > --- a/src/libcamera/v4l2_videodevice.cpp
> > > +++ b/src/libcamera/v4l2_videodevice.cpp
> > > @@ -539,6 +539,7 @@ V4L2VideoDevice::V4L2VideoDevice(const std::string &deviceNode)
> > >   V4L2VideoDevice::V4L2VideoDevice(const MediaEntity *entity)
> > >       : V4L2VideoDevice(entity->deviceNode())
> > >   {
> > > +     watchdog_.timeout.connect(this, &V4L2VideoDevice::watchdogExpired);
> > >   }
> > >
> > >   V4L2VideoDevice::~V4L2VideoDevice()
> > > @@ -1723,6 +1724,9 @@ FrameBuffer *V4L2VideoDevice::dequeueBuffer()
> > >               return nullptr;
> > >       }
> > >
> > > +     if (watchdogDuration_.count())
> > > +             watchdog_.start(watchdogDuration_);
> > > +
> > >       cache_->put(buf.index);
> > >
> > >       FrameBuffer *buffer = it->second;
> > > @@ -1825,6 +1829,8 @@ int V4L2VideoDevice::streamOn()
> > >       }
> > >
> > >       state_ = State::Streaming;
> > > +     if (watchdogDuration_.count())
> > > +             watchdog_.start(watchdogDuration_);
> > >
> > >       return 0;
> > >   }
> > > @@ -1849,6 +1855,9 @@ int V4L2VideoDevice::streamOff()
> > >       if (state_ != State::Streaming && queuedBuffers_.empty())
> > >               return 0;
> > >
> > > +     if (watchdogDuration_.count())
> > > +             watchdog_.stop();
> > > +
> > >       ret = ioctl(VIDIOC_STREAMOFF, &bufferType_);
> > >       if (ret < 0) {
> > >               LOG(V4L2, Error)
> > > @@ -1876,6 +1885,51 @@ int V4L2VideoDevice::streamOff()
> > >       return 0;
> > >   }
> > >
> > > +/**
> > > + * \brief Set the dequeue timeout value
> > > + * \param[in] msec The timeout value to be used

I'd call the parameter timeout instead of msec, the units are specified
by the chrono type.

> > > + *
> > > + * Sets a timeout value, given by \a msec, that will be used by a watchdog timer
> > > + * to ensure buffer dequeue events are periodically occurring when the device is
> > > + * streaming. The watchdog timer is only active when the device is streaming, so
> > > + * it is not necessary to disable it when the device stops streaming. The timeout
> > > + * value can be safely updated at any time.
> > > + *
> > > + * If the timer expires, the \ref V4L2VideoDevice::dequeueTimeout signal is
> > > + * emitted. This can typically be used by pipeline handlers to be notified of
> > > + * stalled devices.
> > > + *
> > > + * Set \a msec to 0 to disable the watchdog timer.
> > > + */
> > > +void V4L2VideoDevice::setDequeueTimeout(std::chrono::milliseconds msec)
> >
> > Same here as well. I guess you take in a `utils::Duration msec` and
> > assign to watchdogDuration_ below (given you have utils::Duration
> > watchdogDuration_ too).
> >
> > > +{
> > > +     watchdogDuration_ = msec;
> > > +
> > > +     watchdog_.stop();
> > > +     if (watchdogDuration_.count() && state_ == State::Streaming)
> > > +             watchdog_.start(msec);
> > > +}
> > > +
> > > +/**
> > > + * \var V4L2VideoDevice::dequeueTimeout
> > > + * \brief A Signal emitted when the dequeue watchdog timer expires
> > > + */
> > > +
> > > +/**
> > > + * \brief Slot to handle an expired dequeue timer.

s/.$//

> > > + *
> > > + * When this slot is called, the time between successive dequeue events is over
> > > + * the required timeout. Emit the \ref V4L2VideoDevice::dequeueTimeout signal.
> > > + */
> > > +void V4L2VideoDevice::watchdogExpired()
> > > +{
> > > +     LOG(V4L2, Warning)
> > > +             << "Dequeue timer of " << watchdogDuration_.count()
> > > +             << " ms has expired!";

If watchdogDuration_ was stored as a utils::Duration, you could write

             << "Dequeue timer of " << watchdogDuration_ << " has expired!";

Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

Would you like to submit a new version with utils::Duration here, or
keep std::chrono::milliseconds ?

> > > +
> > > +     dequeueTimeout.emit();
> > > +}
> > > +
> > >   /**
> > >    * \brief Create a new video device instance from \a entity in media device
> > >    * \a media

-- 
Regards,

Laurent Pinchart