On Wed, Jul 8, 2026 at 10:25 AM Mukesh Kumar Chaurasiya (IBM)
[off-list ref] wrote:

When building with LLVM=1 for architectures like powerpc where
CONFIG_DMA_SHARED_BUFFER is not enabled, the build fails with:

  ld.lld: error: undefined symbol: dma_resv_reset_max_fences
  >>> referenced by helpers.c
  >>>               rust/helpers/helpers.o:(rust_helper_dma_resv_unlock)

The issue occurs because:
1. CONFIG_DEBUG_MUTEXES=y is enabled
2. CONFIG_DMA_SHARED_BUFFER is not enabled
3. dma_resv_reset_max_fences() is declared in the header when
   CONFIG_DEBUG_MUTEXES is set
4. But the function is only compiled in drivers/dma-buf/dma-resv.c,
   which is only built when CONFIG_DMA_SHARED_BUFFER is enabled
5. Rust helpers call dma_resv_unlock() which calls
   dma_resv_reset_max_fences(), causing an undefined symbol

Fix this by compiling `dma-resv.c` file only when CONFIG_DMA_SHARED_BUFFER
is enabled.

Fixes: 9b836641d3bf ("rust: helpers: Add bindings/wrappers for dma_resv_lock")
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <redacted>

Andreas sent a similar one to:

  https://lore.kernel.org/rust-for-linux/20260708-dma-shared-buffer-config-v1-1-8c1571000855@kernel.org/ (local)

This is earlier, but please see his approach & Sashiko's note.

Backlinking here for reference.

Cheers,
Miguel