[PATCH v3] libcamera: debayer_cpu: Sync DMABUFs

[Kieran Bingham]

Quoting Robert Mader (2024-09-16 15:11:25)
> Using `DMA_BUF_IOCTL_SYNC` is required for DMABUFs in order to ensure
> correct output. Not doing so currently results in occasional tearing
> and/or backlashes in GL/VK clients that use the buffers directly for
> rendering.
> 
> An alternative approach to have the sync code in `MappedFrameBuffer` was
> considered but rejected for now, in order to allow clients more
> flexibility.
> 
> Signed-off-by: Robert Mader <robert.mader at collabora.com>
> 
> ---
> 
> Changes in v3:
>  - add syncBufferForCPU() helper function
> 
> Changes in v2:
>  - sync input buffer as well
>  - update commit title accordingly
>  - small changes to the commit message
>  - linting fixes, should pass now
> ---
>  src/libcamera/software_isp/debayer_cpu.cpp | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/src/libcamera/software_isp/debayer_cpu.cpp b/src/libcamera/software_isp/debayer_cpu.cpp
> index 077f7f4b..3748bd7c 100644
> --- a/src/libcamera/software_isp/debayer_cpu.cpp
> +++ b/src/libcamera/software_isp/debayer_cpu.cpp
> @@ -12,8 +12,11 @@
>  #include "debayer_cpu.h"
>  
>  #include <stdlib.h>
> +#include <sys/ioctl.h>
>  #include <time.h>
>  
> +#include <linux/dma-buf.h>
> +
>  #include <libcamera/formats.h>
>  
>  #include "libcamera/internal/bayer_format.h"
> @@ -718,6 +721,17 @@ void DebayerCpu::process4(const uint8_t *src, uint8_t *dst)
>         }
>  }
>  
> +static void syncBufferForCPU(FrameBuffer *buffer, uint64_t syncFlags)

I think these functions (including timeDiff below) should be wrapped in
an annoymous namespace for the libcamera code style.

But as the timeDiff is already in this form - they can both be converted
after. (or before if you want to do the fix up)

> +{
> +       for (const FrameBuffer::Plane &plane : buffer->planes()) {
> +               const int fd = plane.fd.get();
> +               struct dma_buf_sync sync = { syncFlags };
> +
> +               if (ioctl(fd, DMA_BUF_IOCTL_SYNC, &sync) < 0)
> +                       LOG(Debayer, Error) << "Syncing buffer FD " << fd << "failed: " << errno;

This could be rewrapped easily

			LOG(Debayer, Error)
				<< "Syncing buffer FD " << fd << "failed: " << errno;

But we can't reference errno directly from LOG() either, as mentioned in
the previous version:

Easiest cleanup is probably:

		int ret;

		ret = ioctl(fd, DMA_BUF_IOCTL_SYNC, &sync);
		if (ret < 0) {
			ret = errno;
			LOG(Debayer, Error)
				<< "Syncing buffer FD " << fd << "failed: "
				<< strerror(-ret);

		}

Could also print the sync flags too to know which one has failed?

With that handled:

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

> +       }
> +}
> +
>  static inline int64_t timeDiff(timespec &after, timespec &before)
>  {
>         return (after.tv_sec - before.tv_sec) * 1000000000LL +
> @@ -733,6 +747,9 @@ void DebayerCpu::process(FrameBuffer *input, FrameBuffer *output, DebayerParams
>                 clock_gettime(CLOCK_MONOTONIC_RAW, &frameStartTime);
>         }
>  
> +       syncBufferForCPU(input, DMA_BUF_SYNC_START | DMA_BUF_SYNC_READ);
> +       syncBufferForCPU(output, DMA_BUF_SYNC_START | DMA_BUF_SYNC_WRITE);
> +
>         green_ = params.green;
>         red_ = swapRedBlueGains_ ? params.blue : params.red;
>         blue_ = swapRedBlueGains_ ? params.red : params.blue;
> @@ -760,6 +777,9 @@ void DebayerCpu::process(FrameBuffer *input, FrameBuffer *output, DebayerParams
>  
>         metadata.planes()[0].bytesused = out.planes()[0].size();
>  
> +       syncBufferForCPU(output, DMA_BUF_SYNC_END | DMA_BUF_SYNC_WRITE);
> +       syncBufferForCPU(input, DMA_BUF_SYNC_END | DMA_BUF_SYNC_READ);
> +
>         /* Measure before emitting signals */
>         if (measuredFrames_ < DebayerCpu::kLastFrameToMeasure &&
>             ++measuredFrames_ > DebayerCpu::kFramesToSkip) {
> -- 
> 2.46.0
>