[libcamera-devel] [PATCH v1] v4l2_videodevice: Disable the watchdog timer when no buffers are queued

[Kieran Bingham]

Hi Naush,

Quoting Naushir Patuck via libcamera-devel (2022-05-05 09:48:24)
> Only enable/reset the watchdog timer when there are buffers queued in the V4L2
> device. Otherwise, we may trigger spurious warnings when the watchdog times out
> even if there are no buffers queued in the device.

aha yes - I can see how that was tripping up on python interactive
sessions or otherwise underflowing when it's not at all a fault of the
V4L2VideoDevice.


> 
> Signed-off-by: Naushir Patuck <naush at raspberrypi.com>
> ---
>  src/libcamera/v4l2_videodevice.cpp | 22 +++++++++++++++-------
>  1 file changed, 15 insertions(+), 7 deletions(-)
> 
> diff --git a/src/libcamera/v4l2_videodevice.cpp b/src/libcamera/v4l2_videodevice.cpp
> index 5b4637b1a39e..430715afd554 100644
> --- a/src/libcamera/v4l2_videodevice.cpp
> +++ b/src/libcamera/v4l2_videodevice.cpp
> @@ -1662,8 +1662,11 @@ int V4L2VideoDevice::queueBuffer(FrameBuffer *buffer)
>                 return ret;
>         }
>  
> -       if (queuedBuffers_.empty())
> +       if (queuedBuffers_.empty()) {
>                 fdBufferNotifier_->setEnabled(true);
> +               if (watchdogDuration_)
> +                       watchdog_.start(std::chrono::duration_cast<std::chrono::milliseconds>(watchdogDuration_));
> +       }

I guess this could also be set outside of the if (queuedBuffer_.empty())
- but it would artificially delay the watchdog every time a buffer was
queued. In the event that more than one buffer is required to be queued
(to satisfy internal requirements perhaps?) that might actually be
beneficial ... But I think either way is fine.

>  
>         queuedBuffers_[buf.index] = buffer;
>  
> @@ -1742,16 +1745,21 @@ FrameBuffer *V4L2VideoDevice::dequeueBuffer()
>                 return nullptr;
>         }
>  
> -       if (watchdogDuration_.count())
> -               watchdog_.start(std::chrono::duration_cast<std::chrono::milliseconds>(watchdogDuration_));
> -
>         cache_->put(buf.index);
>  
>         FrameBuffer *buffer = it->second;
>         queuedBuffers_.erase(it);
>  
> -       if (queuedBuffers_.empty())
> +       if (queuedBuffers_.empty()) {
>                 fdBufferNotifier_->setEnabled(false);
> +               watchdog_.stop();
> +       } else if (watchdogDuration_) {
> +               /*
> +                * Restart the watchdog timer if there are buffers still queued
> +                * in the device.
> +                */
> +               watchdog_.start(std::chrono::duration_cast<std::chrono::milliseconds>(watchdogDuration_));

Why do we need/have all these casts? Is either watchdogDuration_ not a
duration? or is watchdog_.start() not accepting a duration? Either of
those would remove a lot of casting surely?

watchdogDuration_ is a utils::Duration which stores std::nano, and I see
Timer start takes a std::chrono::milliseconds. I think it would make
sense to add a 'void start(std::chrono::duration)' to the timer class
and simplify these casts. But that doesn't have to be fixed in this
patch.

Would you like to do that as a patch on top? If you don't want to let me
know and I'll handle it after this patch is merged.


Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>


> +       }
>  
>         buffer->metadata_.status = buf.flags & V4L2_BUF_FLAG_ERROR
>                                  ? FrameMetadata::FrameError
> @@ -1847,7 +1855,7 @@ int V4L2VideoDevice::streamOn()
>         }
>  
>         state_ = State::Streaming;
> -       if (watchdogDuration_.count())
> +       if (watchdogDuration_ && !queuedBuffers_.empty())
>                 watchdog_.start(std::chrono::duration_cast<std::chrono::milliseconds>(watchdogDuration_));
>  
>         return 0;
> @@ -1924,7 +1932,7 @@ void V4L2VideoDevice::setDequeueTimeout(utils::Duration timeout)
>         watchdogDuration_ = timeout;
>  
>         watchdog_.stop();
> -       if (watchdogDuration_.count() && state_ == State::Streaming)
> +       if (watchdogDuration_ && state_ == State::Streaming && !queuedBuffers_.empty())
>                 watchdog_.start(std::chrono::duration_cast<std::chrono::milliseconds>(timeout));
>  }
>  
> -- 
> 2.25.1
>