[PATCH v1 0/2] drm/msm: followup - map page-less imported sg_tables

[Jianfeng Liu]

Hi Rob,

this is the follow-up I promised: it fixes the two remaining map
paths that still consume struct page/sg->length of imported
sg_tables, and therefore completes the DMABUF_DEBUG=y story when
applied on top of your series [1].

Test results on x1e78100 (Snapdragon X1E78100, DMABUF_DEBUG=y,
kernel v7.3-rc4 based), which is the machine that originally
reported the UCHE translation faults and the one hardware test
environment for imports of buffers not first exported by drm/msm:

 - v7.3-rc4 stock: arm-smmu UCHE translation faults during hardware
   video decode in clapper/chromium (bisected to 143755bdabaa9)

 - your series alone: video plays via the userspace copy fallback,
   zero GPU faults, but a WARN storm from __arm_lpae_unmap()
   (472 traces within a minute of video playback) - every map of a
   page-less sg_table silently maps nothing, so the matching unmap
   finds no PTE and WARNs.  This matches your cover letter saying
   the map paths are not addressed by the series.  Your patch 2
   ("mmap imported dma-bufs via the exporter") in particular works:
   a test importing a linux,cma-heap buffer via
   DRM_IOCTL_PRIME_FD_TO_HANDLE and mmaps it both through the heap
   fd and through msm's GEM mmap sees the same memory through both
   mappings, including writes visible in both directions.

 - your series + this series: zero arm-smmu faults, zero io-pgtable
   WARNs, and hardware video decode displays correctly in clapper
   and chromium.  The GPU per-process pagetable path is exercised
   with real decoder capture buffers (videobuf2-dma-contig, 2MB
   frames) and maps them from their DMA addresses.

Patch 1 exports iommu_get_dma_domain(), which msm needs to look up
the dma_addr -> phys mapping of imported buffers through the msm
drm device's DMA-API domain.  On platforms where the drm device is
direct mapped (like mine: ae01000.display-controller is in no
iommu_group) the lookup degenerates to the identity; on platforms
where it sits behind a translated IOMMU the translation is needed.

Happy to rebase on whatever your tree looks like - and I can rerun
the full test matrix (WARN count, fault count, kmssink scanout of
real V4L2 frames, chromium/clapper hardware decode) on any revision.

[1] <20260926183051.25754-1-robin.clark@xxxxxxxxxxxxxxxx>



Jianfeng Liu (2):
  iommu: export iommu_get_dma_domain()
  drm/msm: map page-less imported sg_tables from their DMA addresses

 drivers/gpu/drm/msm/msm_gem_vma.c |  9 ++++
 drivers/gpu/drm/msm/msm_iommu.c   | 90 ++++++++++++++++++++++++++++++-
 drivers/gpu/drm/msm/msm_mmu.h     | 13 +++++
 drivers/iommu/iommu.c             |  1 +
 4 files changed, 111 insertions(+), 2 deletions(-)

---
base-commit: d6882ed4e5b3970a13d721a07d2737c4831cdced
branch: msm-map-followup-v1

-- 
2.47.3