[PATCH RFC 0/4] rust: dma: bridge zerocopy-derived types into the transmute byte-safety bound

[SeungJong Ha via B4 Relay <devnull+engineer.jjhama.gmail.com@kernel.org>]

DMA-coherent allocations (CoherentAllocation/Coherent/dma::Pool) bound
their element type on kernel::transmute::{AsBytes, FromBytes}. This RFC
lets a type satisfy that bound by deriving zerocopy's byte-safety traits
instead of a hand-written unsafe impl.

The bound cannot be switched to zerocopy wholesale (some DMA structs are
unions that IntoBytes cannot derive), and a blanket bridge impl is
rejected by coherence. So the series bridges the two per type:

  1. add the bridge macro impl_transmute_via_zerocopy!, which emits the
     transmute impls only for a zerocopy-derived type.
  2. re-export zerocopy::Immutable from the prelude.
  3-4. worked example: convert nova-core's GspMem and msgq POD types.

This series was prepared with the Claude Code AI assistant (model
claude-opus-4-8): it drafted the macro, the nova-core conversion and the
changelogs, which the submitter reviewed and takes responsibility for. It
was verified by building nova-core on rust-next and a negative test
confirming IntoBytes rejects mis-sized padding. See
Documentation/process/coding-assistants.rst.

Assisted-by: Claude-Code:claude-opus-4-8
Signed-off-by: SeungJong Ha <engineer.jjhama@gmail.com>
---
SeungJong Ha (4):
      rust: transmute: add `impl_transmute_via_zerocopy!` macro
      rust: prelude: re-export `zerocopy::Immutable`
      gpu: nova-core: gsp: derive zerocopy traits for the msgq POD types
      gpu: nova-core: gsp: convert GspMem to zerocopy via the transmute bridge

 drivers/gpu/nova-core/gsp.rs                      | 13 ++-------
 drivers/gpu/nova-core/gsp/cmdq.rs                 | 15 +++++-----
 drivers/gpu/nova-core/gsp/fw.rs                   |  8 +++---
 drivers/gpu/nova-core/gsp/fw/r570_144.rs          |  2 ++
 drivers/gpu/nova-core/gsp/fw/r570_144/bindings.rs |  4 +--
 rust/kernel/prelude.rs                            |  2 ++
 rust/kernel/transmute.rs                          | 35 +++++++++++++++++++++++
 7 files changed, 54 insertions(+), 25 deletions(-)
---
base-commit: 780d569e6c4b422290f5cba319eb904b355d64be
change-id: 20260628-dma-zerocopy-bridge-dc1c96b610cf

Best regards,
--  
SeungJong Ha <engineer.jjhama@gmail.com>