[libcamera-devel] [PATCH v2 1/2] android: Post-pone fences reset in capture result

[Laurent Pinchart]

Hi Jacopo,

Thank you for the patch.

On Mon, Sep 27, 2021 at 11:36:59PM +0200, Jacopo Mondi wrote:
> When a request has been completed and a new capture_result is created
> we assumed all fences had been waited on, hence we set both

Maybe "we assumed we have waited for all the fences to be signalled" ?

> the release and acquisition fences to -1.

s/acquisition/acquire/

same below

> As no buffer is queued to libcamera::Camera for streams of type Mapped,
> their acquisition fences went ignored. Prepare to fix that by
> by moving fences resetting after post-processing, that will be
> instrumented to handle fences in the next patch.
> 
> Also correct the release_fence handling for failed captures, as the
> framework requires the release fences to be set to the acquire fence
> value if the acquire fence has not been waited on.
> 
> Signed-off-by: Jacopo Mondi <jacopo at jmondi.org>
> Reviewed-by: Hirokazu Honda <hiroh at chromium.org>
> ---
>  src/android/camera_device.cpp | 44 ++++++++++++++++++++++++-----------
>  1 file changed, 31 insertions(+), 13 deletions(-)
> 
> diff --git a/src/android/camera_device.cpp b/src/android/camera_device.cpp
> index 21844e5114a9..3c9609d74402 100644
> --- a/src/android/camera_device.cpp
> +++ b/src/android/camera_device.cpp
> @@ -1098,22 +1098,10 @@ void CameraDevice::requestComplete(Request *request)
>  	}
>  	Camera3RequestDescriptor &descriptor = node.mapped();
>  
> -	/*
> -	 * Prepare the capture result for the Android camera stack.
> -	 *
> -	 * The buffer status is set to OK and later changed to ERROR if
> -	 * post-processing/compression fails.
> -	 */
>  	camera3_capture_result_t captureResult = {};
>  	captureResult.frame_number = descriptor.frameNumber_;
>  	captureResult.num_output_buffers = descriptor.buffers_.size();
> -	for (camera3_stream_buffer_t &buffer : descriptor.buffers_) {
> -		buffer.acquire_fence = -1;
> -		buffer.release_fence = -1;
> -		buffer.status = CAMERA3_BUFFER_STATUS_OK;
> -	}
>  	captureResult.output_buffers = descriptor.buffers_.data();
> -	captureResult.partial_result = 1;
>  
>  	/*
>  	 * If the Request has failed, abort the request by notifying the error
> @@ -1128,8 +1116,27 @@ void CameraDevice::requestComplete(Request *request)
>  			    CAMERA3_MSG_ERROR_REQUEST);
>  
>  		captureResult.partial_result = 0;
> -		for (camera3_stream_buffer_t &buffer : descriptor.buffers_)
> +		for (camera3_stream_buffer_t &buffer : descriptor.buffers_) {
> +			CameraStream *cameraStream =
> +				static_cast<CameraStream *>(buffer.stream->priv);
> +
> +			/*
> +			 * Streams of type Direct have been queued to the
> +			 * libcamera::Camera and their acquisition fences has

s/has/have/

> +			 * already been waited on by the CameraWorker.
> +			 *
> +			 * For other stream types signal to the framework the
> +			 * acquisition fence has not been waited on, by setting
> +			 * the release fence to its value.
> +			 */
> +			if (cameraStream->type() == CameraStream::Type::Direct)
> +				buffer.release_fence = -1;
> +			else
> +				buffer.release_fence = buffer.acquire_fence;
> +
> +			buffer.acquire_fence = -1;
>  			buffer.status = CAMERA3_BUFFER_STATUS_ERROR;
> +		}

Blank line here.

>  		callbacks_->process_capture_result(callbacks_, &captureResult);
>  
>  		return;
> @@ -1196,6 +1203,17 @@ void CameraDevice::requestComplete(Request *request)
>  		}
>  	}
>  
> +	/*
> +	 * Finalize the capture result by setting fences and buffer status
> +	 * before executing the callback.
> +	 */
> +	for (camera3_stream_buffer_t &buffer : descriptor.buffers_) {
> +		buffer.acquire_fence = -1;

Ideally, it would be nice to set the acquire_fence to -1 in
CameraWorker::Worker::waitFence(), just after closing the fence fd.
That's not possible yet, as the CameraWorker doesn't have access to the
descriptor. This will be fixed by Umang's work, but I don't think we
should wait until it gets merged. A \todo comment here would be good
though.

If we could set acquire_fence to -1 right after waiting, the above code
would also be simplified, you could write

			buffer.release_fence = buffer.acquire_fence;

regardless of the stream type.

> +		buffer.release_fence = -1;
> +		buffer.status = CAMERA3_BUFFER_STATUS_OK;

This will override the buffer status set to CAMERA3_BUFFER_STATUS_ERROR
in case post-processing fails. I think it would be easier to keep
setting buffer.status to CAMERA3_BUFFER_STATUS_OK at the beginning of
this function to avoid this problem. And if you keep the loop, you could
as well set release_fence to -1 there too, but that's up to you.

> +	}
> +	captureResult.partial_result = 1;
> +
>  	captureResult.result = resultMetadata->get();
>  	callbacks_->process_capture_result(callbacks_, &captureResult);
>  }

-- 
Regards,

Laurent Pinchart