[PATCH v3 1/2] DmaBufAllocator: Add Dma Buffer synchronization function & helper class

[Laurent Pinchart]

On Thu, Nov 21, 2024 at 05:51:31AM +0000, Harvey Yang wrote:
> 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    | 21 ++++++
>  src/libcamera/dma_buf_allocator.cpp           | 75 +++++++++++++++++++
>  2 files changed, 96 insertions(+)
> 
> diff --git a/include/libcamera/internal/dma_buf_allocator.h b/include/libcamera/internal/dma_buf_allocator.h
> index d2a0a0d19..e4073f668 100644
> --- a/include/libcamera/internal/dma_buf_allocator.h
> +++ b/include/libcamera/internal/dma_buf_allocator.h
> @@ -8,6 +8,7 @@
>  #pragma once
>  
>  #include <libcamera/base/flags.h>
> +#include <libcamera/base/shared_fd.h>
>  #include <libcamera/base/unique_fd.h>
>  
>  namespace libcamera {
> @@ -35,6 +36,26 @@ private:
>  	DmaBufAllocatorFlag type_;
>  };
>  
> +class DmaSyncer final
> +{
> +public:
> +	enum class SyncType {
> +		Read = 0,
> +		Write,
> +		ReadWrite,
> +	};
> +
> +	explicit DmaSyncer(SharedFD fd, SyncType type = SyncType::ReadWrite);

Why is this calss copyable ?

> +
> +	~DmaSyncer();
> +
> +private:
> +	void sync(uint64_t step);
> +
> +	SharedFD fd_;
> +	uint64_t flags_ = 0;
> +};
> +
>  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..c1c2103d6 100644
> --- a/src/libcamera/dma_buf_allocator.cpp
> +++ b/src/libcamera/dma_buf_allocator.cpp
> @@ -205,4 +205,79 @@ 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.
> + *
> + * It's used when the user needs to access a dma-buf with CPU, mostly mapped
> + * with MappedFrameBuffer, so that the buffer is synchronized between CPU and
> + * ISP.
> + */
> +
> +/**
> + * \enum DmaSyncer::SyncType
> + * \brief Read and/or write access via the CPU map
> + * \var DmaSyncer::Read
> + * \brief Indicates that the mapped dma-buf will be read by the client via the
> + * CPU map
> + * \var DmaSyncer::Write
> + * \brief Indicates that the mapped dm-buf will be written by the client via the
> + * CPU map
> + * \var DmaSyncer::ReadWrite
> + * \brief Indicates that the mapped dma-buf will be read and written by the
> + * client via the CPU map
> + */
> +
> +/**
> + * \fn DmaSyncer::DmaSyncer(SharedFD fd, SyncType type = 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
> + */
> +DmaSyncer::DmaSyncer(SharedFD fd, SyncType type)
> +	: fd_(fd)
> +{
> +	switch (type) {
> +	case SyncType::Read:
> +		flags_ = DMA_BUF_SYNC_READ;
> +		break;
> +	case SyncType::Write:
> +		flags_ = DMA_BUF_SYNC_WRITE;
> +		break;
> +	case SyncType::ReadWrite:
> +		flags_ = DMA_BUF_SYNC_RW;
> +		break;
> +	}
> +
> +	sync(DMA_BUF_SYNC_START);
> +}
> +
> +DmaSyncer::~DmaSyncer()
> +{
> +	sync(DMA_BUF_SYNC_END);
> +}
> +
> +void DmaSyncer::sync(uint64_t step)
> +{
> +	struct dma_buf_sync sync = {
> +		.flags = flags_ | step
> +	};
> +
> +	int ret;
> +	do {
> +		ret = ioctl(fd_.get(), DMA_BUF_IOCTL_SYNC, &sync);
> +	} while (ret && (errno == EINTR || errno == EAGAIN));
> +
> +	if (ret) {
> +		ret = errno;
> +		LOG(DmaBufAllocator, Error)
> +			<< "Unable to sync dma fd: " << fd_.get()
> +			<< ", err: " << strerror(ret)
> +			<< ", flags: " << sync.flags;
> +	}
> +}
> +
>  } /* namespace libcamera */

-- 
Regards,

Laurent Pinchart