[PATCH 0/2] fpga: add dma-buf based FPGA programming interface

[Aravind Thokala <aravind.thokala@amd.com>]

Some systems need to load large FPGA configuration images. The FPGA
subsystem allows loading images from the filesystem, but this requires
the entire image to be loaded into kernel memory first. For drivers
that need a DMA-capable buffer for programming, the data is then
copied again into DMA memory. This creates needless memory pressure
and delays due to the extra copy.

This series adds dma-buf support that allows userspace to allocate a
buffer directly from a DMA heap, write the FPGA image into it, and
pass the file descriptor to the kernel via ioctl — skipping the
intermediate kernel buffer entirely.

Userspace flow:
  1. Allocate buffer from /dev/dma_heap/ (e.g., CMA heap)
  2. mmap the buffer and write the FPGA image into it
  3. ioctl(/dev/fpgaX, FPGA_IOCTL_LOAD_DMA_BUF, &dmabuf_fd)

The dma-buf logic is implemented as a separate layer on top of the
FPGA manager, keeping buffer management separate from the write path.
Individual FPGA drivers opt in by calling fpga_dmabuf_register().
---
This work is based on the approach discussed in [1].

[1] https://lore.kernel.org/all/20231122053035.3758124-1-nava.kishore.manne@amd.com/
---
Aravind Thokala (2):
  fpga: Add dma-buf interface for FPGA programming
  fpga: versal: add dma-buf programming support

 .../userspace-api/ioctl/ioctl-number.rst      |   1 +
 MAINTAINERS                                   |   1 +
 drivers/fpga/Kconfig                          |   9 +
 drivers/fpga/Makefile                         |   2 +
 drivers/fpga/fpga-dmabuf.c                    | 198 ++++++++++++++++++
 drivers/fpga/versal-fpga.c                    |  33 ++-
 include/linux/fpga/fpga-dmabuf.h              |  22 ++
 include/linux/fpga/fpga-mgr.h                 |   1 +
 include/uapi/linux/fpga.h                     |  15 ++
 9 files changed, 281 insertions(+), 1 deletion(-)
 create mode 100644 drivers/fpga/fpga-dmabuf.c
 create mode 100644 include/linux/fpga/fpga-dmabuf.h
 create mode 100644 include/uapi/linux/fpga.h

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2.34.1