buffer.h

// Copyright(c) 2017, Intel Corporation
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/**
 * @file buffer.h
 * @brief Functions for allocating and sharing system memory with an FPGA
 * accelerator
 *
 * To share memory between a software application and an FPGA accelerator,
 * these functions set up system components (e.g. an IOMMU) to allow
 * accelerator access to a provided memory region.
 *
 * There are a number of restrictions on what memory can be shared, depending
 * on platform capabilities. Usually, FPGA accelerators to not have access to
 * virtual address mappings of the CPU, so they can only access physical
 * addresses. To support this, the OPAE C library on Linux uses hugepages to
 * allocate large, contiguous pages of physical memory that can be shared with
 * an accelerator. It also supports sharing memory that has already been
 * allocated by an application, as long as that memory satisfies the
 * requirements of being physically contigous and page-aligned.
 */

#ifndef __FPGA_BUFFER_H__
#define __FPGA_BUFFER_H__

#include <opae/types.h>

#ifdef __cplusplus
extern "C" {
#endif

/**
 * Prepare a shared memory buffer
 *
 * Prepares a memory buffer for shared access between an accelerator and the calling
 * process. This may either include allocation of physical memory, or
 * preparation of already allocated memory for sharing. The latter case is
 * indicated by supplying the FPGA_BUF_PREALLOCATED flag.
 *
 * This function will ask the driver to pin the indicated memory (make it
 * non-swappable), and program the IOMMU to allow access from the accelerator. If the
 * buffer was not pre-allocated (flag FPGA_BUF_PREALLOCATED), the function
 * will also allocate physical memory of the requested size and map the
 * memory into the caller's process' virtual address space. It returns in
 * 'wsid' an fpga_buffer object that can be used to program address registers
 * in the accelerator for shared access to the memory.
 *
 * When using FPGA_BUF_PREALLOCATED, the input len must be a non-zero multiple
 * of the page size, else the function returns FPGA_INVALID_PARAM. When not
 * using FPGA_BUF_PREALLOCATED, the input len is rounded up to the nearest
 * multiple of page size.
 *
 * @param[in]  handle     Handle to previously opened accelerator resource
 * @param[in]  len        Length of the buffer to allocate/prepare in bytes
 * @param[inout] buf_addr Virtual address of buffer. Contents may be NULL (OS
 *                        will choose mapping) or non-NULL (OS will take
 *                        contents as a hint for the virtual address).
 * @param[out] wsid       Handle to the allocated/prepared buffer to be used
 *                        with other functions
 * @param[in]  flags      Flags. FPGA_BUF_PREALLOCATED indicates that memory
 *                        pointed at in '*buf_addr' is already allocated an
 *                        mapped into virtual memory. FPGA_BUF_READ_ONLY
 *                        pins pages with only read access from the FPGA.
 * @returns FPGA_OK on success. FPGA_NO_MEMORY if the requested memory could
 * not be allocated. FPGA_INVALID_PARAM if invalid parameters were provided, or
 * if the parameter combination is not valid. FPGA_EXCEPTION if an internal
 * exception occurred while trying to access the handle.
 *
 * @note As a special case, when FPGA_BUF_PREALLOCATED is present in flags,
 * if len == 0 and buf_addr == NULL, then the function returns FPGA_OK if
 * pre-allocated buffers are supported. In this case, a return value other
 * than FPGA_OK indicates that pre-allocated buffers are not supported.
 */
fpga_result fpgaPrepareBuffer(fpga_handle handle,
			      uint64_t len,
			      void **buf_addr, uint64_t *wsid, int flags);

/**
 * Release a shared memory buffer
 *
 * Releases a previously prepared shared buffer. If the buffer was allocated
 * using fpgaPrepareBuffer (FPGA_BUF_PREALLOCATED was not specified), this call
 * will deallocate/free that memory. Otherwise, it will only be returned to
 * it's previous state (pinned/unpinned, cached/non-cached).
 *
 * @param[in]  handle   Handle to previously opened accelerator resource
 * @param[in]  wsid     Handle to the allocated/prepared buffer
 * @returns FPGA_OK on success. FPGA_INVALID_PARAM if invalid parameters were
 * provided, or if the parameter combination is not valid. FPGA_EXCEPTION if an
 * internal exception occurred while trying to access the handle.
 */
fpga_result fpgaReleaseBuffer(fpga_handle handle, uint64_t wsid);

/**
 * Retrieve base IO address for buffer
 *
 * This function is used to acquire the physical base address (on some platforms
 * called IO Virtual Address or IOVA) for a shared buffer identified by wsid.
 *
 * @note This function will disappear once the APIs for secure sharing of
 * buffer addresses is implemented.
 *
 * @param[in]  handle   Handle to previously opened accelerator resource
 * @param[in]  wsid     Buffer handle / workspace ID referring to the buffer for
 *                      which the IO address is requested
 * @param[out] ioaddr   Pointer to memory where the IO address will be returned
 * @returns FPGA_OK on success. FPGA_INVALID_PARAM if invalid parameters were
 * provided, or if the parameter combination is not valid. FPGA_EXCEPTION if an
 * internal exception occurred while trying to access the handle.
 * FPGA_NOT_FOUND if `wsid` does not refer to a previously shared buffer.
 */
fpga_result fpgaGetIOAddress(fpga_handle handle, uint64_t wsid,
			     uint64_t *ioaddr);

/**
 * Bind IOMMU shared virtual addressing
 *
 * When PCIe PASID, ATS and PRS capabilities are enabled, some platforms
 * support binding the IOMMU to user space virtual addresses.
 *
 * @param[in]  handle   Handle to previously opened accelerator resource
 * @param[out] pasid    Process address space ID, set if not NULL.
 * @returns FPGA_OK on success and FPGA_NOT_SUPPORTED otherwise.
 */
fpga_result fpgaBindSVA(fpga_handle handle, uint32_t *pasid);

#ifdef __cplusplus
} // extern "C"
#endif // __cplusplus

#endif // __FPGA_BUFFER_H__