linux-toradex.git/drivers/dma-buf/Makefile, branch master

dma-buf: introduce initial file I/O infrastructure

2026-10-14T13:36:02+00:00

The goal is to be able to natively use dma-buf in the read-write / IO
path. This patch adds basic building blocks serving as a glue and API
between drivers and upper layer subsystems providing the uAPI. Later
patches implement it for NVMe raw block devices and expose it to the
user space via io_uring.

There are two main objects. struct dma_buf_io_ctx and struct
dma_buf_io_map. The ctx is used during initial registration and serves
as an interface between the upper layer user like io_uring and to the
importer subsystem / driver. The map represents the actual dma map
established for the target device[s] with dma_buf_map_attachment() and
stored in a device specific format. The context is created via a new
file operation ->init_dma_buf_io_ctx.

The ctx-map separation exists to facilitate map invalidation (see
dma_buf_io_invalidate_mappings()). A ctx can create
multiple maps during its lifetime, but there can only be no more than
one (active) map attached to it. Invalidation drops the active map
if present, and any new I/O request will try to create a new one.

The primary task of dma_buf_io_map is to count requests using it
and wait for their completion when we want to destroy the DMA map.

[un]mapping and any work with dma addresses is delegated to the
importer driver via an ops table stored in the ctx, see struct
dma_buf_io_ops. Only the target driver / subsystem knows about devices
it wants to use the dma-buf with, especially in case of multi-device
filesystems or stacking in the future.

Acked-by: Matthew Brost
Tested-by: Matthew Brost
Acked-by: Christian König
Signed-off-by: Pavel Begunkov
Link: https://patch.msgid.link/49e24334953262e85d5616c9afde88c680e4f3a3.1791975048.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe

dma-buf: Remove the old selftest

2026-04-16T10:34:00+00:00

Nothing uses this framework anymore, remove it.

Signed-off-by: Jason Gunthorpe 
Reviewed-by: Christian König 
Signed-off-by: Christian König 
Link: https://lore.kernel.org/r/5-v1-0a349a394eff+14110-dmabuf_kunit_jgg@nvidia.com

dma-buf: Change st-dma-fence-chain.c to use kunit

2026-04-16T10:34:00+00:00

Modernize the open coded test framework by using kunit.

Signed-off-by: Jason Gunthorpe 
Reviewed-by: Christian König 
Signed-off-by: Christian König 
Link: https://lore.kernel.org/r/4-v1-0a349a394eff+14110-dmabuf_kunit_jgg@nvidia.com

dma-buf: Change st-dma-fence-unwrap.c to use kunit

2026-04-16T10:34:00+00:00

Modernize the open coded test framework by using kunit.

Signed-off-by: Jason Gunthorpe 
Reviewed-by: Christian König 
Signed-off-by: Christian König 
Link: https://lore.kernel.org/r/3-v1-0a349a394eff+14110-dmabuf_kunit_jgg@nvidia.com

dma-buf: Change st-dma-fence.c to use kunit

2026-04-16T10:34:00+00:00

Modernize the open coded test framework by using kunit.

Add a num_online_cpus() check to test_race_signal_callback() as the
default kunit.py runs the VM with a single CPU and this test depends on
two truly parallel kthreads. Skip it instead of hanging.

Signed-off-by: Jason Gunthorpe 
Reviewed-by: Christian König 
Signed-off-by: Christian König 
Link: https://lore.kernel.org/r/2-v1-0a349a394eff+14110-dmabuf_kunit_jgg@nvidia.com

dma-buf: Change st-dma-resv.c to use kunit

2026-04-16T10:34:00+00:00

Modernize the open coded test framework by using kunit.

The kunit tool can be used to build a kernel and run it in a VM with:

$ tools/testing/kunit/kunit.py run --build_dir build_kunit_x86_64 --arch x86_64 --kunitconfig ./drivers/dma-buf/.kunitconfig

Along with the other ways to run kunits.

To make the kunit tool work like this the DMABUF_KUNIT_TEST kconfig must
select DMA_SHARED_BUFFER to get it turned on without building a driver
using it.

Signed-off-by: Jason Gunthorpe 
Reviewed-by: Christian König 
Signed-off-by: Christian König 
Link: https://lore.kernel.org/r/1-v1-0a349a394eff+14110-dmabuf_kunit_jgg@nvidia.com

dma-buf: Remove DMA-BUF sysfs stats

2026-01-19T13:40:01+00:00

Commit bdb8d06dfefd ("dmabuf: Add the capability to expose DMA-BUF stats
in sysfs") added dmabuf statistics to sysfs in 2021 under
CONFIG_DMABUF_SYSFS_STATS. After being used in production, performance
problems were discovered leading to its deprecation in 2022 in commit
e0a9f1fe206a ("dma-buf: deprecate DMABUF_SYSFS_STATS"). Some of the
problems with this interface were discussed in my LPC 2025 talk. [1][2]

Android was probably the last user of the interface, which has since
been migrated to use the dmabuf BPF iterator [3] to obtain the same
information more cheaply. As promised in that series, now that the
longterm stable 6.18 kernel has been released let's remove the sysfs
dmabuf statistics from the kernel.

[1] https://www.youtube.com/watch?v=D83qygudq9c
[2] https://lpc.events/event/19/contributions/2118/
[3] https://lore.kernel.org/all/20250522230429.941193-1-tjmercier@google.com/

Signed-off-by: T.J. Mercier 
Reviewed-by: Christian König 
Signed-off-by: Sumit Semwal 
Link: https://patch.msgid.link/20260116190517.3268458-1-tjmercier@google.com

dma-buf: provide phys_vec to scatter-gather mapping routine

2025-11-20T19:02:19+00:00

Add dma_buf_phys_vec_to_sgt() and dma_buf_free_sgt() helpers to convert
an array of MMIO physical address ranges into scatter-gather tables with
proper DMA mapping.

These common functions are a starting point and support any PCI
drivers creating mappings from their BAR's MMIO addresses. VFIO is one
case, as shortly will be RDMA. We can review existing DRM drivers to
refactor them separately. We hope this will evolve into routines to
help common DRM that include mixed CPU and MMIO mappings.

Compared to the dma_map_resource() abuse this implementation handles
the complicated PCI P2P scenarios properly, especially when an IOMMU
is enabled:

 - Direct bus address mapping without IOVA allocation for
   PCI_P2PDMA_MAP_BUS_ADDR, using pci_p2pdma_bus_addr_map(). This
   happens if the IOMMU is enabled but the PCIe switch ACS flags allow
   transactions to avoid the host bridge.

   Further, this handles the slightly obscure, case of MMIO with a
   phys_addr_t that is different from the physical BAR programming
   (bus offset). The phys_addr_t is converted to a dma_addr_t and
   accommodates this effect. This enables certain real systems to
   work, especially on ARM platforms.

 - Mapping through host bridge with IOVA allocation and DMA_ATTR_MMIO
   attribute for MMIO memory regions (PCI_P2PDMA_MAP_THRU_HOST_BRIDGE).
   This happens when the IOMMU is enabled and the ACS flags are forcing
   all traffic to the IOMMU - ie for virtualization systems.

 - Cases where P2P is not supported through the host bridge/CPU. The
   P2P subsystem is the proper place to detect this and block it.

Helper functions fill_sg_entry() and calc_sg_nents() handle the
scatter-gather table construction, splitting large regions into
UINT_MAX-sized chunks to fit within sg->length field limits.

Since the physical address based DMA API forbids use of the CPU list
of the scatterlist this will produce a mangled scatterlist that has
a fully zero-length and NULL'd CPU list. The list is 0 length,
all the struct page pointers are NULL and zero sized. This is stronger
and more robust than the existing mangle_sg_table() technique. It is
a future project to migrate DMABUF as a subsystem away from using
scatterlist for this data structure.

Reviewed-by: Kevin Tian 
Reviewed-by: Nicolin Chen 
Reviewed-by: Jason Gunthorpe 
Tested-by: Alex Mastro 
Tested-by: Nicolin Chen 
Signed-off-by: Leon Romanovsky 
Acked-by: Christian König 
Acked-by: Ankit Agrawal 
Link: https://lore.kernel.org/r/20251120-dmabuf-vfio-v9-6-d7f71607f371@nvidia.com
Signed-off-by: Alex Williamson

dma-buf: cleanup dma_fence_unwrap implementation

2022-05-30T12:16:32+00:00

Move the code from the inline functions into exported functions.

Signed-off-by: Christian König 
Acked-by: Daniel Vetter 
Link: https://patchwork.freedesktop.org/patch/msgid/20220518135844.3338-3-christian.koenig@amd.com

dma-buf: add dma_fence_unwrap v2

2022-03-25T13:18:28+00:00

Add a general purpose helper to deep dive into dma_fence_chain/dma_fence_array
structures and iterate over all the fences in them.

This is useful when we need to flatten out all fences in those structures.

v2: some selftests cleanup, improved function naming and documentation

Signed-off-by: Christian König 
Reviewed-by: Daniel Vetter 
Link: https://patchwork.freedesktop.org/patch/msgid/20220311110244.1245-1-christian.koenig@amd.com