[PATCH] libcamera: debayer_cpu: Sync output buffer

[Robert Mader]

Using `DMA_BUF_IOCTL_SYNC` is required for dmabufs in order to ensure
correct results. Not doing so currently results in occasional tearing
and/or backlashes in GL/VK clients that use the buffers directly for
rendering.

Signed-off-by: Robert Mader <robert.mader at collabora.com>
---
 src/libcamera/software_isp/debayer_cpu.cpp | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/src/libcamera/software_isp/debayer_cpu.cpp b/src/libcamera/software_isp/debayer_cpu.cpp
index 077f7f4b..6c953b03 100644
--- a/src/libcamera/software_isp/debayer_cpu.cpp
+++ b/src/libcamera/software_isp/debayer_cpu.cpp
@@ -11,7 +11,9 @@
 
 #include "debayer_cpu.h"
 
+#include <linux/dma-buf.h>
 #include <stdlib.h>
+#include <sys/ioctl.h>
 #include <time.h>
 
 #include <libcamera/formats.h>
@@ -733,6 +735,16 @@ void DebayerCpu::process(FrameBuffer *input, FrameBuffer *output, DebayerParams
 		clock_gettime(CLOCK_MONOTONIC_RAW, &frameStartTime);
 	}
 
+	for (const FrameBuffer::Plane &plane : output->planes()) {
+		const int fd = plane.fd.get();
+		struct dma_buf_sync sync = { DMA_BUF_SYNC_START };
+
+		sync.flags |= DMA_BUF_SYNC_WRITE;
+
+		if (ioctl (fd, DMA_BUF_IOCTL_SYNC, &sync) < 0)
+			LOG(Debayer, Error) << "Syncing buffer FD " << fd << "failed: " << errno;
+	}
+
 	green_ = params.green;
 	red_ = swapRedBlueGains_ ? params.blue : params.red;
 	blue_ = swapRedBlueGains_ ? params.red : params.blue;
@@ -760,6 +772,16 @@ void DebayerCpu::process(FrameBuffer *input, FrameBuffer *output, DebayerParams
 
 	metadata.planes()[0].bytesused = out.planes()[0].size();
 
+	for (const FrameBuffer::Plane &plane : output->planes()) {
+		const int fd = plane.fd.get();
+		struct dma_buf_sync sync = { DMA_BUF_SYNC_END };
+
+		sync.flags |= DMA_BUF_SYNC_WRITE;
+
+		if (ioctl (fd, DMA_BUF_IOCTL_SYNC, &sync) < 0)
+			LOG(Debayer, Error) << "Syncing buffer FD " << fd << "failed: " << errno;
+	}
+
 	/* Measure before emitting signals */
 	if (measuredFrames_ < DebayerCpu::kLastFrameToMeasure &&
 	    ++measuredFrames_ > DebayerCpu::kFramesToSkip) {
-- 
2.46.0