[PATCH v4] libcamera: debayer_cpu: Sync DMABUFs

[Kieran Bingham]

Quoting Robert Mader (2024-09-16 17:12:31)
> 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 v4:
>  - Fixed errno handling
>  - Added sync flags to error message
>  - Wrapped syncBufferForCPU() and timeDiff() into an anonymous namespace
> 
> 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 | 30 ++++++++++++++++++++++
>  1 file changed, 30 insertions(+)
> 
> diff --git a/src/libcamera/software_isp/debayer_cpu.cpp b/src/libcamera/software_isp/debayer_cpu.cpp
> index 077f7f4b..96cf2c71 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"
> @@ -718,12 +721,33 @@ void DebayerCpu::process4(const uint8_t *src, uint8_t *dst)
>         }
>  }
>  
> +namespace {
> +
> +static void syncBufferForCPU(FrameBuffer *buffer, uint64_t syncFlags)

Now these are in an annoymous namespace, they don't need to be static -
but that can be fixed while applying perhaps or ignored for now if no
further version is required otherwise.

I'm happy to merge, but under software_isp/* I think we should have an
Acked-by/Reviewed-by by one of the SoftISP developers.

Milan, Hans ? Are you happy with this patch? Is there any impact with
the Intel devices for instance?

--
Kieran




> +{
> +       for (const FrameBuffer::Plane &plane : buffer->planes()) {
> +               const int fd = plane.fd.get();
> +               struct dma_buf_sync sync = { syncFlags };
> +               int ret;
> +
> +               ret = ioctl(fd, DMA_BUF_IOCTL_SYNC, &sync);
> +               if (ret < 0) {
> +                       ret = errno;
> +                       LOG(Debayer, Error)
> +                               << "Syncing buffer FD " << fd << " with flags "
> +                               << syncFlags << " failed: " << strerror(-ret);
> +               }
> +       }
> +}
> +
>  static inline int64_t timeDiff(timespec &after, timespec &before)
>  {
>         return (after.tv_sec - before.tv_sec) * 1000000000LL +
>                (int64_t)after.tv_nsec - (int64_t)before.tv_nsec;
>  }
>  
> +} /* namespace */
> +
>  void DebayerCpu::process(FrameBuffer *input, FrameBuffer *output, DebayerParams params)
>  {
>         timespec frameStartTime;
> @@ -733,6 +757,9 @@ 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 +787,9 @@ 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
>