[PATCH 14/16] libcamera: software_isp: Track statistics buffers

[Milan Zamazal]

As a preparation for passing the shared statistics buffers to IPA, this
patch introduces tracking statistics buffer ids.

SofwareIsp::availableStats_ is a queue of ids of the buffers available
for use.  When a fresh statistics buffer is needed, its id is retrieved
from there and once the buffer is no longer needed, it's put back there,
in a method invoked by a signal.  This is similar to what the hardware
pipelines do.

We use buffers' file descriptors as buffer ids.  The statistics buffers
will be shared with the IPA, SwIspStats and debayering and we need their
common identification everywhere.  The buffer file descriptors are
shared unchanged so they can be used for the purpose, avoiding a need to
pass a special mapping to the IPA and debayering on initialization.

Note that the statistics buffer id is still actually unused, this will
be changed once the buffers are shared with the IPA.

Signed-off-by: Milan Zamazal <mzamazal at redhat.com>
---
 .../libcamera/internal/software_isp/software_isp.h  |  1 +
 src/libcamera/software_isp/software_isp.cpp         | 13 +++++++++++--
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/include/libcamera/internal/software_isp/software_isp.h b/include/libcamera/internal/software_isp/software_isp.h
index a6ba4a07..5959e86e 100644
--- a/include/libcamera/internal/software_isp/software_isp.h
+++ b/include/libcamera/internal/software_isp/software_isp.h
@@ -102,6 +102,7 @@ private:
 	DebayerParams debayerParams_;
 	std::queue<uint32_t> availableParams_;
 	bool allocateParamsBuffers(const unsigned int bufferCount);
+	std::queue<uint32_t> availableStats_;
 	std::unique_ptr<SwStatsCpu> allocateStatsBuffers(
 		std::vector<SharedFD> &fdStats,
 		const unsigned int bufferCount);
diff --git a/src/libcamera/software_isp/software_isp.cpp b/src/libcamera/software_isp/software_isp.cpp
index 1e224b6f..c4ad22be 100644
--- a/src/libcamera/software_isp/software_isp.cpp
+++ b/src/libcamera/software_isp/software_isp.cpp
@@ -191,6 +191,7 @@ std::unique_ptr<SwStatsCpu> SoftwareIsp::allocateStatsBuffers(
 		unsigned int bufferId = shared.fd().get();
 		fdStats.emplace_back(shared.fd());
 		sharedStats->emplace(bufferId, std::move(shared));
+		availableStats_.push(bufferId);
 	}
 
 	auto stats = std::make_unique<SwStatsCpu>(std::move(sharedStats));
@@ -413,11 +414,18 @@ void SoftwareIsp::process(uint32_t frame, FrameBuffer *input, FrameBuffer *outpu
 		while (availableParams_.empty())
 			;
 	}
+	if (availableStats_.empty()) {
+		LOG(SoftwareIsp, Error) << "Statistics buffer underrun";
+		/* Well, busy loop, but this situation shouldn't normally happen. */
+		while (availableStats_.empty())
+			;
+	}
 
 	const uint32_t paramsBufferId = availableParams_.front();
 	availableParams_.pop();
+	const uint32_t statsBufferId = availableStats_.front();
+	availableStats_.pop();
 	ipa_->prepare(frame, paramsBufferId);
-	const uint32_t statsBufferId = 0;
 	debayer_->invokeMethod(&DebayerCpu::process,
 			       ConnectionTypeQueued, frame,
 			       statsBufferId, paramsBufferId, input, output);
@@ -443,8 +451,9 @@ void SoftwareIsp::statsReady(uint32_t frame, const uint32_t statsBufferId)
 	ispStatsReady.emit(frame, statsBufferId);
 }
 
-void SoftwareIsp::statsProcessed([[maybe_unused]] const uint32_t statsBufferId)
+void SoftwareIsp::statsProcessed(const uint32_t statsBufferId)
 {
+	availableStats_.push(statsBufferId);
 }
 
 void SoftwareIsp::inputReady(FrameBuffer *input)
-- 
2.44.1