[PATCH v4] libcamera: debayer_cpu: Sync DMABUFs

[Kieran Bingham]

Quoting Milan Zamazal (2024-09-18 10:55:47)
> Kieran Bingham <kieran.bingham at ideasonboard.com> writes:
> 
> > 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?
> 
> I'm fine with the patch (with the exception below) and it works fine on
> Debix (with only ~0,5% performance penalty).  It would be nice if Hans
> tested it on Intel.
> 
> > --
> > 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);
> 
> I think `ret' and not `-ret' should be used here.  And I would drop
> `ret = errno' above and use errno here directly.  I'm not sure why
> Kieran suggested exactly this -- using strerror is right but changing
> the sign seems wrong (tested in my environment).

This is a pattern we've used throughout libcamera. It's not advised to
use errno directly in a stream operation ( << ) because other parts of
the stream or calls, or even the construction of the LOG() class could
do something that also sets errno.

So we take a copy of errno as soon as the error is detected.

Yes - I'm wrong on the -ret in that instance. Sorry - I got confused
because we would only return a negative error value - but in this
instance we are in a void function that doesn't return anything.
(there's no point I think).

But yes I inverted the value - sorry. As long as 'errno' is not directly
used in the LOG() << errno; statements it's fine.

--
Kieran

> 
> >> +               }
> >> +       }
> >> +}
> >> +
> >>  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
> >>
>