[PATCH v4 0/2] gpu: nova: fix incorrect GSP barrier usage

[Gary Guo]

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.

---
Changes in v4:
- Moved barriers to pointer accessor/updater. This does mean unnecessary
  barrier in failed polling path but the code path is not critical.
  I mentioned about providing full acq/rel semantics, but ended up not
  doing it because LOAD->LOAD barrier is sufficient for the GSP->CPU
  messaging path, so it's best to still mention about the actually needed
  ordering only.
- Link to v3: https://patch.msgid.link/20260819-rust-barrier-v3-0-d5b7bd7e6624@xxxxxxxxxxx

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@xxxxxxxxxxx

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@xxxxxxxxxx

To: Danilo Krummrich <dakr@xxxxxxxxxx>
To: Alice Ryhl <aliceryhl@xxxxxxxxxx>
To: Alexandre Courbot <acourbot@xxxxxxxxxx>
To: David Airlie <airlied@xxxxxxxxx>
To: Simona Vetter <simona@xxxxxxxx>
Cc: nova-gpu@xxxxxxxxxxxxxxx
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx

---
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 | 41 ++++++++++++++++++++++++---------------
 1 file changed, 25 insertions(+), 16 deletions(-)
---
base-commit: 89c07d98716a13454ec3fd9f97689e812cc71bd4
change-id: 20260609-rust-barrier-63078ea76216

Best regards,
--  
Gary Guo <gary@xxxxxxxxxxx>