linux.git/rust/kernel/dma.rs, branch v7.1-rc2 Linux kernel source tree rust: dma: add from-slice constructors for Coherent and CoherentBox 2026-03-28T13:20:07+00:00 Alexandre Courbot acourbot@nvidia.com 2026-03-26T15:22:07+00:00 816718c611cab2164d718b91ad8204afcd0af81f A very common pattern is to create a block of coherent memory with the content of an already-existing slice of bytes (e.g. a loaded firmware blob). `CoherentBox` makes this easier, but still implies a potentially panicking operation with `copy_from_slice` that requires a `PANIC` comment. Add `from_slice_with_attrs` and `from_slice` methods to both `Coherent` and `CoherentBox` to turn this into a trivial one-step operation. Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org> Reviewed-by: Gary Guo <gary@garyguo.net> Reviewed-by: Danilo Krummrich <dakr@kernel.org> Link: https://patch.msgid.link/20260327-b4-nova-dma-removal-v2-1-616e1d0b5cb3@nvidia.com Signed-off-by: Alexandre Courbot <acourbot@nvidia.com> 
A very common pattern is to create a block of coherent memory with the
content of an already-existing slice of bytes (e.g. a loaded firmware
blob).

`CoherentBox` makes this easier, but still implies a potentially
panicking operation with `copy_from_slice` that requires a `PANIC`
comment.

Add `from_slice_with_attrs` and `from_slice` methods to both `Coherent`
and `CoherentBox` to turn this into a trivial one-step operation.

Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Danilo Krummrich <dakr@kernel.org>
Link: https://patch.msgid.link/20260327-b4-nova-dma-removal-v2-1-616e1d0b5cb3@nvidia.com
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
rust: dma: add CoherentHandle for DMA allocations without kernel mapping 2026-03-28T13:13:23+00:00 Danilo Krummrich dakr@kernel.org 2026-03-21T17:27:47+00:00 6dd782af1eb6be16a80349ea7822f0f8a23bb3e8 Add CoherentHandle, an opaque DMA allocation type for buffers that are only ever accessed by hardware. Unlike Coherent<T>, it does not provide CPU access to the allocated memory. CoherentHandle implicitly sets DMA_ATTR_NO_KERNEL_MAPPING and stores the value returned by dma_alloc_attrs() as an opaque handle (NonNull<c_void>) rather than a typed pointer, since with this flag the C API returns an opaque cookie (e.g. struct page *), not a CPU pointer to the allocated memory. Only the DMA bus address is exposed to drivers; the opaque handle is used solely to free the allocation on drop. This commit is for reference only; there is currently no in-tree user. Signed-off-by: Danilo Krummrich <dakr@kernel.org> Reviewed-by: Alexandre Courbot <acourbot@nvidia.com> Link: https://patch.msgid.link/20260321172749.592387-2-dakr@kernel.org [acourbot: fix conflict in dma.rs.] Signed-off-by: Alexandre Courbot <acourbot@nvidia.com> 
Add CoherentHandle, an opaque DMA allocation type for buffers that are
only ever accessed by hardware. Unlike Coherent<T>, it does not provide
CPU access to the allocated memory.

CoherentHandle implicitly sets DMA_ATTR_NO_KERNEL_MAPPING and stores the
value returned by dma_alloc_attrs() as an opaque handle
(NonNull<c_void>) rather than a typed pointer, since with this flag the
C API returns an opaque cookie (e.g. struct page *), not a CPU pointer
to the allocated memory.

Only the DMA bus address is exposed to drivers; the opaque handle is
used solely to free the allocation on drop.

This commit is for reference only; there is currently no in-tree user.

Signed-off-by: Danilo Krummrich <dakr@kernel.org>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Link: https://patch.msgid.link/20260321172749.592387-2-dakr@kernel.org
[acourbot: fix conflict in dma.rs.]
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
rust: dma: remove DMA_ATTR_NO_KERNEL_MAPPING from public attrs 2026-03-28T13:07:31+00:00 Danilo Krummrich dakr@kernel.org 2026-03-21T17:27:46+00:00 18fb5f1f0289b8217c0c43d54d12bccc201dd640 When DMA_ATTR_NO_KERNEL_MAPPING is passed to dma_alloc_attrs(), the returned CPU address is not a pointer to the allocated memory but an opaque handle (e.g. struct page *). Coherent<T> (or CoherentAllocation<T> respectively) stores this value as NonNull<T> and exposes methods that dereference it and even modify its contents. Remove the flag from the public attrs module such that drivers cannot pass it to Coherent<T> (or CoherentAllocation<T> respectively) in the first place. Instead DMA_ATTR_NO_KERNEL_MAPPING can be supported with an additional opaque type (e.g. CoherentHandle) which does not provide access to the allocated memory. Cc: stable@vger.kernel.org Fixes: ad2907b4e308 ("rust: add dma coherent allocator abstraction") Signed-off-by: Danilo Krummrich <dakr@kernel.org> Reviewed-by: Alice Ryhl <aliceryhl@google.com> Reviewed-by: Alexandre Courbot <acourbot@nvidia.com> Reviewed-by: Gary Guo <gary@garyguo.net> Link: https://patch.msgid.link/20260321172749.592387-1-dakr@kernel.org Signed-off-by: Alexandre Courbot <acourbot@nvidia.com> 
When DMA_ATTR_NO_KERNEL_MAPPING is passed to dma_alloc_attrs(), the
returned CPU address is not a pointer to the allocated memory but an
opaque handle (e.g. struct page *).

Coherent<T> (or CoherentAllocation<T> respectively) stores this value as
NonNull<T> and exposes methods that dereference it and even modify its
contents.

Remove the flag from the public attrs module such that drivers cannot
pass it to Coherent<T> (or CoherentAllocation<T> respectively) in the
first place.

Instead DMA_ATTR_NO_KERNEL_MAPPING can be supported with an additional
opaque type (e.g. CoherentHandle) which does not provide access to the
allocated memory.

Cc: stable@vger.kernel.org
Fixes: ad2907b4e308 ("rust: add dma coherent allocator abstraction")
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260321172749.592387-1-dakr@kernel.org
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
rust: dma: generalize BinaryWriter impl for Coherent<T> 2026-03-27T20:48:18+00:00 Danilo Krummrich dakr@kernel.org 2026-03-25T00:39:16+00:00 d1619a433806c61d240a1eb9b4f03cb33ac40fce Generalize the BinaryWriter implementation from Coherent<[u8]> to Coherent<T> where T: KnownSize + AsBytes + ?Sized. The implementation only uses size() and write_dma(), neither of which depends on the inner type being a byte slice. This allows any Coherent allocation with an AsBytes inner type to be exposed as a debugfs binary file. Acked-by: Gary Guo <gary@garyguo.net> Reviewed-by: Alexandre Courbot <acourbot@nvidia.com> Link: https://patch.msgid.link/20260325003921.3420-2-dakr@kernel.org Signed-off-by: Danilo Krummrich <dakr@kernel.org> 
Generalize the BinaryWriter implementation from Coherent<[u8]> to
Coherent<T> where T: KnownSize + AsBytes + ?Sized. The implementation
only uses size() and write_dma(), neither of which depends on the
inner type being a byte slice.

This allows any Coherent allocation with an AsBytes inner type to be
exposed as a debugfs binary file.

Acked-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Link: https://patch.msgid.link/20260325003921.3420-2-dakr@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
rust: dma: implement BinaryWriter for Coherent<[u8]> 2026-03-25T00:24:11+00:00 Timur Tabi ttabi@nvidia.com 2026-03-19T21:26:55+00:00 01681851393642e10b5cc3f35eb6a1916ee4aff1 Implement the BinaryWriter trait for Coherent<[u8]>, enabling DMA coherent allocations to be exposed as readable binary files. The implementation handles offset tracking and bounds checking, copying data from the coherent allocation to userspace via write_dma(). Signed-off-by: Timur Tabi <ttabi@nvidia.com> Reviewed-by: Alice Ryhl <aliceryhl@google.com> Reviewed-by: Alexandre Courbot <acourbot@nvidia.com> Tested-by: John Hubbard <jhubbard@nvidia.com> Tested-by: Eliot Courtney <ecourtney@nvidia.com> Link: https://patch.msgid.link/20260319212658.2541610-4-ttabi@nvidia.com [ Rebase onto Coherent<T> changes. - Danilo ] Signed-off-by: Danilo Krummrich <dakr@kernel.org> 
Implement the BinaryWriter trait for Coherent<[u8]>, enabling DMA
coherent allocations to be exposed as readable binary files.  The
implementation handles offset tracking and bounds checking, copying data
from the coherent allocation to userspace via write_dma().

Signed-off-by: Timur Tabi <ttabi@nvidia.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Tested-by: John Hubbard <jhubbard@nvidia.com>
Tested-by: Eliot Courtney <ecourtney@nvidia.com>
Link: https://patch.msgid.link/20260319212658.2541610-4-ttabi@nvidia.com
[ Rebase onto Coherent<T> changes. - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
rust: dma: remove dma::CoherentAllocation<T> 2026-03-23T21:36:00+00:00 Danilo Krummrich dakr@kernel.org 2026-03-21T18:18:08+00:00 55fd681cdd8599edc82013674cbf87c2f22d58f8 Now that everything has been converted to the new dma::Coherent<T> API, remove dma::CoherentAllocation<T>. Suggested-by: Gary Guo <gary@garyguo.net> Reviewed-by: Gary Guo <gary@garyguo.net> Link: https://patch.msgid.link/DH8O47F2GM1Z.3H3E13RSKIV22@kernel.org Signed-off-by: Danilo Krummrich <dakr@kernel.org> 
Now that everything has been converted to the new dma::Coherent<T> API,
remove dma::CoherentAllocation<T>.

Suggested-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/DH8O47F2GM1Z.3H3E13RSKIV22@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
rust: dma: add Coherent:init() and Coherent::init_with_attrs() 2026-03-23T21:36:00+00:00 Danilo Krummrich dakr@kernel.org 2026-03-20T19:45:40+00:00 40251bac0e00818b0b632d2d154e4f1f815849eb Analogous to Coherent::zeroed() and Coherent::zeroed_with_attrs(), add Coherent:init() and Coherent::init_with_attrs() which both take an impl Init<T, E> argument initializing the DMA coherent memory. Compared to CoherentInit, Coherent::init() is a one-shot constructor that runs an Init closure and immediately exposes the DMA handle, whereas CoherentInit is a multi-stage initializer that provides safe &mut T access by withholding the DMA address until converted to Coherent. Reviewed-by: Gary Guo <gary@garyguo.net> Reviewed-by: Alexandre Courbot <acourbot@nvidia.com> Link: https://patch.msgid.link/20260320194626.36263-6-dakr@kernel.org Signed-off-by: Danilo Krummrich <dakr@kernel.org> 
Analogous to Coherent::zeroed() and Coherent::zeroed_with_attrs(), add
Coherent:init() and Coherent::init_with_attrs() which both take an impl
Init<T, E> argument initializing the DMA coherent memory.

Compared to CoherentInit, Coherent::init() is a one-shot constructor
that runs an Init closure and immediately exposes the DMA handle,
whereas CoherentInit is a multi-stage initializer that provides safe
&mut T access by withholding the DMA address until converted to
Coherent.

Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Link: https://patch.msgid.link/20260320194626.36263-6-dakr@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
rust: dma: introduce dma::CoherentBox for memory initialization 2026-03-23T21:35:38+00:00 Danilo Krummrich dakr@kernel.org 2026-03-20T19:45:39+00:00 80f4a7b5138d1c427ee5626e8a796aa6b2994a95 Currently, dma::Coherent cannot safely provide (mutable) access to its underlying memory because the memory might be concurrently accessed by a DMA device. This makes it difficult to safely initialize the memory before handing it over to the hardware. Introduce dma::CoherentBox, a type that encapsulates a dma::Coherent before its DMA address is exposed to the device. dma::CoherentBox can guarantee exclusive access to the inner dma::Coherent and implement Deref and DerefMut. Once the memory is properly initialized, dma::CoherentBox can be converted into a regular dma::Coherent. Reviewed-by: Alice Ryhl <aliceryhl@google.com> Reviewed-by: Gary Guo <gary@garyguo.net> Reviewed-by: Alexandre Courbot <acourbot@nvidia.com> Link: https://patch.msgid.link/20260320194626.36263-5-dakr@kernel.org [ Remove unnecessary trait bounds. - Danilo ] Signed-off-by: Danilo Krummrich <dakr@kernel.org> 
Currently, dma::Coherent cannot safely provide (mutable) access to its
underlying memory because the memory might be concurrently accessed by a
DMA device. This makes it difficult to safely initialize the memory
before handing it over to the hardware.

Introduce dma::CoherentBox, a type that encapsulates a dma::Coherent
before its DMA address is exposed to the device. dma::CoherentBox can
guarantee exclusive access to the inner dma::Coherent and implement
Deref and DerefMut.

Once the memory is properly initialized, dma::CoherentBox can be
converted into a regular dma::Coherent.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Link: https://patch.msgid.link/20260320194626.36263-5-dakr@kernel.org
[ Remove unnecessary trait bounds. - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
rust: dma: add zeroed constructor to `Coherent` 2026-03-23T21:33:23+00:00 Gary Guo gary@garyguo.net 2026-03-20T19:45:38+00:00 f84ecffa3f745572164c1269f20eec2589d432c9 These constructors create a coherent container of a single object instead of slice. They are named `zeroed` and `zeroed_with_attrs` to emphasis that they are created initialized zeroed. It is intended that there'll be new constructors that take `PinInit` instead of zeroing. Signed-off-by: Gary Guo <gary@garyguo.net> Reviewed-by: Alice Ryhl <aliceryhl@google.com> Reviewed-by: Alexandre Courbot <acourbot@nvidia.com> Link: https://patch.msgid.link/20260320194626.36263-4-dakr@kernel.org [ Use kernel import style. - Danilo ] Signed-off-by: Danilo Krummrich <dakr@kernel.org> 
These constructors create a coherent container of a single object
instead of slice. They are named `zeroed` and `zeroed_with_attrs` to
emphasis that they are created initialized zeroed. It is intended that
there'll be new constructors that take `PinInit` instead of zeroing.

Signed-off-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Link: https://patch.msgid.link/20260320194626.36263-4-dakr@kernel.org
[ Use kernel import style. - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
rust: dma: add generalized container for types other than slices 2026-03-23T21:15:03+00:00 Gary Guo gary@garyguo.net 2026-03-20T19:45:37+00:00 d9aee73c56ee971b08173071ad93fa5ebf00a32e Currently, `CoherentAllocation` is concecptually a DMA coherent container of a slice of `[T]` of runtime-checked length. Generalize it by creating `dma::Coherent<T>` which can hold any value of `T`. `Coherent::alloc_with_attrs` is implemented but not yet exposed, as I believe we should not expose the way to obtain an uninitialized coherent region. `Coherent<[T]>` provides a `len` method instead of the previous `count()` method to be consistent with methods on slices. The existing type is re-defined as a type alias of `Coherent<[T]>` to ease transition. Methods in use are not yet removed. Signed-off-by: Gary Guo <gary@garyguo.net> Reviewed-by: Alice Ryhl <aliceryhl@google.com> Reviewed-by: Alexandre Courbot <acourbot@nvidia.com> Link: https://patch.msgid.link/20260320194626.36263-3-dakr@kernel.org Signed-off-by: Danilo Krummrich <dakr@kernel.org> 
Currently, `CoherentAllocation` is concecptually a DMA coherent container
of a slice of `[T]` of runtime-checked length. Generalize it by creating
`dma::Coherent<T>` which can hold any value of `T`.
`Coherent::alloc_with_attrs` is implemented but not yet exposed, as I
believe we should not expose the way to obtain an uninitialized coherent
region.

`Coherent<[T]>` provides a `len` method instead of the previous `count()`
method to be consistent with methods on slices.

The existing type is re-defined as a type alias of `Coherent<[T]>` to ease
transition. Methods in use are not yet removed.

Signed-off-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Link: https://patch.msgid.link/20260320194626.36263-3-dakr@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>