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| author | Leon Romanovsky <leonro@nvidia.com> | 2025-09-09 16:27:29 +0300 |
|---|---|---|
| committer | Marek Szyprowski <m.szyprowski@samsung.com> | 2025-09-12 00:08:07 +0200 |
| commit | eadaa8b255f36ee39ca97d0815c25eeeb1f5d674 (patch) | |
| tree | 479cf0f9d52e0705991efaf05b7d09ede0d9fe79 /Documentation/core-api | |
| parent | b9a62320d83863c40973d548dcd379cd6390da20 (diff) | |
| download | linux-eadaa8b255f36ee39ca97d0815c25eeeb1f5d674.tar.gz linux-eadaa8b255f36ee39ca97d0815c25eeeb1f5d674.tar.bz2 linux-eadaa8b255f36ee39ca97d0815c25eeeb1f5d674.zip | |
dma-mapping: introduce new DMA attribute to indicate MMIO memory
This patch introduces the DMA_ATTR_MMIO attribute to mark DMA buffers
that reside in memory-mapped I/O (MMIO) regions, such as device BARs
exposed through the host bridge, which are accessible for peer-to-peer
(P2P) DMA.
This attribute is especially useful for exporting device memory to other
devices for DMA without CPU involvement, and avoids unnecessary or
potentially detrimental CPU cache maintenance calls.
DMA_ATTR_MMIO is supposed to provide dma_map_resource() functionality
without need to call to special function and perform branching when
processing generic containers like bio_vec by the callers.
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Link: https://lore.kernel.org/r/6f058ec395c5348014860dbc2eed348c17975843.1757423202.git.leonro@nvidia.com
Diffstat (limited to 'Documentation/core-api')
| -rw-r--r-- | Documentation/core-api/dma-attributes.rst | 18 |
1 files changed, 18 insertions, 0 deletions
diff --git a/Documentation/core-api/dma-attributes.rst b/Documentation/core-api/dma-attributes.rst index 1887d92e8e92..0bdc2be65e57 100644 --- a/Documentation/core-api/dma-attributes.rst +++ b/Documentation/core-api/dma-attributes.rst @@ -130,3 +130,21 @@ accesses to DMA buffers in both privileged "supervisor" and unprivileged subsystem that the buffer is fully accessible at the elevated privilege level (and ideally inaccessible or at least read-only at the lesser-privileged levels). + +DMA_ATTR_MMIO +------------- + +This attribute indicates the physical address is not normal system +memory. It may not be used with kmap*()/phys_to_virt()/phys_to_page() +functions, it may not be cacheable, and access using CPU load/store +instructions may not be allowed. + +Usually this will be used to describe MMIO addresses, or other non-cacheable +register addresses. When DMA mapping this sort of address we call +the operation Peer to Peer as a one device is DMA'ing to another device. +For PCI devices the p2pdma APIs must be used to determine if +DMA_ATTR_MMIO is appropriate. + +For architectures that require cache flushing for DMA coherence +DMA_ATTR_MMIO will not perform any cache flushing. The address +provided must never be mapped cacheable into the CPU. |