[PATCH 1/2] DmaBufAllocator: Add Dma Buffer synchronization function & helper class

[Cheng-Hao Yang]

Hi Milan,

On Tue, Nov 12, 2024 at 10:00 PM Milan Zamazal <mzamazal at redhat.com> wrote:
>
> Hi Harvey,
>
> thank you for the patch.
>
> Harvey Yang <chenghaoyang at chromium.org> writes:
>
> > To synchronize CPU access with mmap and hardware access on DMA buffers,
> > using `DMA_BUF_IOCTL_SYNC` is required. This patch adds a function and
> > a helper class to allow users to sync buffers more easily.
> >
> > Signed-off-by: Han-Lin Chen <hanlinchen at chromium.org>
> > Co-developed-by: Harvey Yang <chenghaoyang at chromium.org>
> > Signed-off-by: Harvey Yang <chenghaoyang at chromium.org>
> > ---
> >  .../libcamera/internal/dma_buf_allocator.h    | 33 +++++++
> >  src/libcamera/dma_buf_allocator.cpp           | 88 +++++++++++++++++++
> >  2 files changed, 121 insertions(+)
> >
> > diff --git a/include/libcamera/internal/dma_buf_allocator.h b/include/libcamera/internal/dma_buf_allocator.h
> > index d2a0a0d19..2b9b99678 100644
> > --- a/include/libcamera/internal/dma_buf_allocator.h
> > +++ b/include/libcamera/internal/dma_buf_allocator.h
> > @@ -23,6 +23,19 @@ public:
> >
> >       using DmaBufAllocatorFlags = Flags<DmaBufAllocatorFlag>;
> >
> > +     enum class SyncStep {
> > +             Start = 0,
> > +             End
> > +     };
> > +
> > +     enum class SyncType {
> > +             Read = 0,
> > +             Write,
> > +             ReadWrite,
> > +     };
> > +
> > +     static void sync(int fd, SyncStep step, SyncType type);
> > +
> >       DmaBufAllocator(DmaBufAllocatorFlags flags = DmaBufAllocatorFlag::CmaHeap);
> >       ~DmaBufAllocator();
> >       bool isValid() const { return providerHandle_.isValid(); }
> > @@ -35,6 +48,26 @@ private:
> >       DmaBufAllocatorFlag type_;
> >  };
> >
> > +class DmaSyncer final
> > +{
> > +public:
> > +     explicit DmaSyncer(int fd,
> > +                        DmaBufAllocator::SyncType type = DmaBufAllocator::SyncType::ReadWrite)
> > +             : fd_(fd), type_(type)
> > +     {
> > +             DmaBufAllocator::sync(fd_, DmaBufAllocator::SyncStep::Start, type_);
> > +     }
> > +
> > +     ~DmaSyncer()
> > +     {
> > +             DmaBufAllocator::sync(fd_, DmaBufAllocator::SyncStep::End, type_);
> > +     }
> > +
> > +private:
> > +     int fd_;
> > +     DmaBufAllocator::SyncType type_;
> > +};
> > +
> >  LIBCAMERA_FLAGS_ENABLE_OPERATORS(DmaBufAllocator::DmaBufAllocatorFlag)
> >
> >  } /* namespace libcamera */
> > diff --git a/src/libcamera/dma_buf_allocator.cpp b/src/libcamera/dma_buf_allocator.cpp
> > index be6efb89f..3ae98c168 100644
> > --- a/src/libcamera/dma_buf_allocator.cpp
> > +++ b/src/libcamera/dma_buf_allocator.cpp
> > @@ -78,6 +78,79 @@ LOG_DEFINE_CATEGORY(DmaBufAllocator)
> >   * \brief A bitwise combination of DmaBufAllocator::DmaBufAllocatorFlag values
> >   */
> >
> > +/**
> > + * \enum DmaBufAllocator::SyncStep
> > + * \brief Either start or end of the synchronization
> > + * \var DmaBufAllocator::Start
> > + * \brief Indicates the start of a map access session
> > + * \var DmaBufAllocator::End
> > + * \brief Indicates the end of a map access session
> > + */
> > +
> > +/**
> > + * \enum DmaBufAllocator::SyncType
> > + * \brief Read and/or write access via the CPU map
> > + * \var DmaBufAllocator::Read
> > + * \brief Indicates that the mapped dma-buf will be read by the client via the
> > + * CPU map
> > + * \var DmaBufAllocator::Write
> > + * \brief Indicates that the mapped dm-buf will be written by the client via the
> > + * CPU map
> > + * \var DmaBufAllocator::ReadWrite
> > + * \brief Indicates that the mapped dma-buf will be rad andd written by the
>
> s/rad andd/read and/

Done

>
> > + * client via the CPU map
> > + */
> > +
> > +/**
> > + * \brief Synchronize CPU access and hardware access
> > + * \param[in] fd The dma-buf's file descriptor to be synchronized
> > + * \param[in] step Either start or end of the synchronization
> > + * \param[in] type Read and/or write access during CPU mmap
> > + *
> > + * The client is expected to call this function with
> > + * DmaBufAllocator::SyncStep::Start and DmaBufAllocator::SyncStep::End at the
> > + * start and end of buffer access respectively.
> > + */
> > +void DmaBufAllocator::sync(int fd, DmaBufAllocator::SyncStep step, DmaBufAllocator::SyncType type)
> > +{
> > +     uint64_t flags = 0;
> > +     switch (step) {
> > +     case DmaBufAllocator::SyncStep::Start:
> > +             flags = DMA_BUF_SYNC_START;
> > +             break;
> > +     case DmaBufAllocator::SyncStep::End:
> > +             flags = DMA_BUF_SYNC_END;
> > +             break;
> > +     }
> > +
> > +     switch (type) {
> > +     case DmaBufAllocator::SyncType::Read:
> > +             flags = flags | DMA_BUF_SYNC_READ;
> > +             break;
> > +     case DmaBufAllocator::SyncType::Write:
> > +             flags = flags | DMA_BUF_SYNC_WRITE;
> > +             break;
> > +     case DmaBufAllocator::SyncType::ReadWrite:
> > +             flags = flags | DMA_BUF_SYNC_RW;
> > +             break;
> > +     }
> > +
> > +     struct dma_buf_sync sync = {
> > +             .flags = flags
> > +     };
> > +
> > +     int ret;
> > +     do {
> > +             ret = ioctl(fd, DMA_BUF_IOCTL_SYNC, &sync);
> > +     } while (!ret && (errno == EINTR || errno == EAGAIN));
>
> Shouldn't it be `ret' rather than `!ret'?

Ah right! Thanks for the catch!

>
> > +
> > +     if (ret) {
> > +             LOG(DmaBufAllocator, Error) << "Unable to sync dma fd: " << fd
> > +                                         << ", step: " << static_cast<int>(step)
> > +                                         << ", type: " << static_cast<int>(type);
>
> Wouldn't it be useful to log errno?

Done

BR,
Harvey


>
> > +     }
> > +}
> > +
> >  /**
> >   * \brief Construct a DmaBufAllocator of a given type
> >   * \param[in] type The type(s) of the dma-buf providers to allocate from
> > @@ -205,4 +278,19 @@ UniqueFD DmaBufAllocator::alloc(const char *name, std::size_t size)
> >               return allocFromHeap(name, size);
> >  }
> >
> > +/**
> > + * \class DmaSyncer
> > + * \brief Helper class for dma-buf's synchronization
> > + *
> > + * This class wraps a userspace dma-buf's synchronization process with an
> > + * object's lifetime.
> > + */
> > +
> > +/**
> > + * \fn DmaSyncer::DmaSyncer(int fd, DmaBufAllocator::SyncType type = DmaBufAllocator::SyncType::ReadWrite)
> > + * \brief Construct a DmaSyncer with a dma-buf's fd and the access type
> > + * \param[in] fd The dma-buf's file descriptor to synchronize
> > + * \param[in] type Read and/or write access via the CPU map
> > + */
> > +
> >  } /* namespace libcamera */
>