Currently Nova GSP code uses Rust barriers, which equivalent to LKMM SMP
barriers. This does not provide sufficient ordering for DMA operations on
AArch64. Fix this to be using the newly introduced `dma_mb(Ordering)` API.

Also, there is an incorrect placement of barrier, which is also fixed.

This should wait until v7.3-rc1 backmerge to drm-rust-next occurs.

---
Changes in v3:
- Drop abstraction changes which are already picked.
- Improve ordering comment messages.
- Replace control dependency reliance with explicit barrier.
- Link to v2: https://patch.msgid.link/20260609-rust-barrier-v2-0-30fcc48e1cd0@garyguo.net

Changes in v2:
- Dropped `Acquire` and `Release` aliases of `Full` (Joel)
- Use macros to implement most `MemoryBarrier`
- Split Nova change to GSP->CPU commit and CPU->GSP commit (Joel)
- Link to v1: https://patch.msgid.link/20260402152443.1059634-2-gary@kernel.org

To: Danilo Krummrich <dakr@kernel.org>
To: Alice Ryhl <aliceryhl@google.com>
To: Alexandre Courbot <acourbot@nvidia.com>
To: David Airlie <airlied@gmail.com>
To: Simona Vetter <simona@ffwll.ch>
Cc: nova-gpu@lists.linux.dev
Cc: dri-devel@lists.freedesktop.org
Cc: linux-kernel@vger.kernel.org

---
Gary Guo (2):
      gpu: nova-core: fix barrier usage in CPU->GSP messaging path
      gpu: nova-core: fix barrier usage in GSP->CPU messaging path

 drivers/gpu/nova-core/gsp/cmdq.rs | 34 ++++++++++++++++++++--------------
 1 file changed, 20 insertions(+), 14 deletions(-)
---
base-commit: e6664f2b33db9b6811eb4cec109f06cb2b4f458d
change-id: 20260609-rust-barrier-63078ea76216

Best regards,
--  
Gary Guo <gary@garyguo.net>