[PATCH 04/16] libcamera: software_isp: Track unused parameters buffers

[Milan Zamazal]

As a preparation for introducing a ring of parameters buffers, this
patch introduces tracking of parameters buffers available for use.

SofwareIsp::availableParams_ is a queue of ids of the buffers available
for use.  When a fresh parameter 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.

If a parameters buffer is requested but there is no free available, it
is an erroneous situation.  To recover from it, we have currently no
better mechanism than to wait for an available buffer.  Simply returning
from the processing would mean the finishing signals are not called,
resulting in e.g. the input buffer not being returned.  This is
different from the hardware pipelines, which are structured somewhat
differently.

We use buffers' file descriptors as buffer ids.  The parameters buffers
will be shared with the IPA 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 id->buffer mapping to the IPA and debayering on initialization.

Note that the parameters buffer id is still actually unused and the only
buffer currently used is still copied when passed to debayering.  This
patch is just preparation for followup patches that will introduce
multiple buffers.

Signed-off-by: Milan Zamazal <mzamazal at redhat.com>
---
 .../internal/software_isp/software_isp.h       |  2 ++
 src/libcamera/software_isp/software_isp.cpp    | 18 +++++++++++++++---
 2 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/include/libcamera/internal/software_isp/software_isp.h b/include/libcamera/internal/software_isp/software_isp.h
index fc9200dd..74f5b952 100644
--- a/include/libcamera/internal/software_isp/software_isp.h
+++ b/include/libcamera/internal/software_isp/software_isp.h
@@ -10,6 +10,7 @@
 #include <functional>
 #include <map>
 #include <memory>
+#include <queue>
 #include <stdint.h>
 #include <string>
 #include <tuple>
@@ -95,6 +96,7 @@ private:
 	Thread ispWorkerThread_;
 	SharedMemObject<DebayerParams> sharedParams_;
 	DebayerParams debayerParams_;
+	std::queue<uint32_t> availableParams_;
 	bool allocateParamsBuffers();
 	DmaBufAllocator dmaHeap_;
 
diff --git a/src/libcamera/software_isp/software_isp.cpp b/src/libcamera/software_isp/software_isp.cpp
index 3f41b71d..a9865398 100644
--- a/src/libcamera/software_isp/software_isp.cpp
+++ b/src/libcamera/software_isp/software_isp.cpp
@@ -149,6 +149,10 @@ bool SoftwareIsp::allocateParamsBuffers()
 		return false;
 	}
 
+	ASSERT(sharedParams_.fd().get() >= 0);
+	const uint32_t bufferId = sharedParams_.fd().get();
+	availableParams_.push(bufferId);
+
 	return true;
 }
 
@@ -360,8 +364,15 @@ void SoftwareIsp::stop()
  */
 void SoftwareIsp::process(uint32_t frame, FrameBuffer *input, FrameBuffer *output)
 {
-	/* \todo Provide a real value */
-	constexpr uint32_t paramsBufferId = 0;
+	if (availableParams_.empty()) {
+		LOG(SoftwareIsp, Error) << "Parameters buffer underrun";
+		/* Well, busy loop, but this situation shouldn't normally happen. */
+		while (availableParams_.empty())
+			;
+	}
+
+	const uint32_t paramsBufferId = availableParams_.front();
+	availableParams_.pop();
 	ipa_->prepare(frame, paramsBufferId);
 	debayer_->invokeMethod(&DebayerCpu::process,
 			       ConnectionTypeQueued, frame, paramsBufferId, input, output, debayerParams_);
@@ -372,8 +383,9 @@ void SoftwareIsp::saveIspParams([[maybe_unused]] uint32_t paramsBufferId)
 	debayerParams_ = *sharedParams_;
 }
 
-void SoftwareIsp::releaseIspParams([[maybe_unused]] uint32_t paramsBufferId)
+void SoftwareIsp::releaseIspParams(uint32_t paramsBufferId)
 {
+	availableParams_.push(paramsBufferId);
 }
 
 void SoftwareIsp::setSensorCtrls(const ControlList &sensorControls)
-- 
2.44.1