Re: [RFC PATCH v2 00/10] dma-mapping: Add preservation of direct allocations

[Jason Gunthorpe]

On Wed, Jul 08, 2026 at 11:48:44PM +0000, Samiullah Khawaja wrote:
> This is an RFC v2 to discuss the preservation of DMA allocations for
> devices that are using direct allocation mode. Note preservation here
> means preservation of physical memory using KHO only. IOVAs and IOMMU
> mappings are out of scope.
> 
> The complexity and need of this was discussed in the thread mentioned
> below. It was proposed to allow preservation of only a subset of
> allocations with minimum support. Offline discussion with Will Deacon
> concluded that this series is still needed, because we still want to use
> coherent allocations for Arm sMMUv3 ste/cds, so sending this v2.

Was this before or after concluding that ARM was OK with using
cachable memory?

>  include/linux/dma-direct.h        |  29 +++++
>  include/linux/dma-map-ops.h       |  10 ++
>  include/linux/dma-mapping.h       | 100 ++++++++++++++
>  include/linux/kho/abi/dma_alloc.h |  32 +++++
>  kernel/dma/Kconfig                |  12 ++
>  kernel/dma/Makefile               |   1 +
>  kernel/dma/coherent.c             |  11 ++
>  kernel/dma/contiguous.c           |  27 ++++
>  kernel/dma/direct.c               | 189 +++++++++++++++++++++++++++
>  kernel/dma/direct_test.c          | 208 ++++++++++++++++++++++++++++++
>  kernel/dma/mapping.c              | 132 +++++++++++++++++++
>  kernel/dma/pool.c                 |  17 +++
>  12 files changed, 768 insertions(+)

Because this seems like quite a big change to swallow compared to just
using iommu pages.h

Jason