Hi everyone,

This is v3 of the "DMA per allocation kernel mappings" series.

Changes since v2:
- Dropped rcar-du patch in favor of just using dma_get_sgtable_attrs()
  in patch 2
- Patch 1
  - Switched to drm_warn_once()
  - Moved flag definition from include/uapi/ to include/drm/drm_dumb_buffers.h
  - Reworded commit message
- Patch 2
  - Added change for rcar-du: s/dma_get_sgtable()/dma_get_sgtable_attrs()/
- Patch 3
  - Added back DRM_MODE_DUMB_KERNEL_MAP flag to all drivers calling
    drm_gem_dma_dumb_create_internal()
  - Expanded commit message to cover display drivers needing the kernel
    mapping to do scan out


This is an attempt to revive Rob Herring's "DMA per allocation kernel
mappings" [1] series from 2019. This series stacks on top of my recent
"drm/gem-dma: Support dedicated DMA device for allocation" series [2].
Many of the allocation paths are touched by both.

The 3 driver conversions from the original series are not included, as
the changes have landed in some other form.

Patch 1 adds the kernel internal DRM_MODE_DUMB_KERNEL_MAP flag.

Patch 2 adds the dma_attr field to drm_gem_dma_object, and converts
the GEM DMA helpers to use the dma_*_attrs() variant of the DMA API.

Patch 3 adds support for DRM_MODE_DUMB_KERNEL_MAP to the GEM DMA
helpers by setting the DMA_ATTR_NO_KERNEL_MAPING attribute for requests
without the DRM_MODE_DUMB_KERNEL_MAP flag.


All existing callers of drm_gem_dma_dumb_create_internal() will have
DRM_MODE_DUMB_KERNEL_MAP set to maintain existing behavior.

I have also started to convert the exynos driver to use the GEM DMA
helpers. I also plan on looking into the rockchip driver, but that one
has a separate IOMMU path that needs to be handled. I might copy the
approach used in the exynos driver to deal with it.


Changes compared to the original version from Rob (v1):
- Link to original v1:
  https://lore.kernel.org/dri-devel/20191021214550.1461-1-robh@kernel.org/
- Rebased onto renamed GEM DMA helpers
- New patch for rcar-du
- Patch 2
  - Make drm_mode_create_dumb_ioctl() emit warning if args->flags is not zero
- Patch 3
  - Made vc4_bo_purge() use dma_free_attrs(); this is the other location
    of DMA API used with drm_gem_dma_object outside the helpers
  - Expanded commit message
- Patch 4
  - Added kernal mapping check in drm_fb_dma_get_scanout_buffer() and
    drm_gem_dma_vmap().
  - Made drm_gem_dma_print_info() show "vaddr=(no mapping)" for objects
    allocated without kernel mapping
  - Dropped existing DRM_MODE_DUMB_KERNEL_MAP flag addition in various
    drivers
  - Added DRM_MODE_DUMB_KERNEL_MAP flag to adp_drm_gem_dumb_create()
  - Added flags field kerneldoc for drm_gem_dma_create_with_handle()

I dropped all the original Reviewed-by tags, as it's been 5 years since
the changes were first posted, and also because the code has changed a
lot.

Please have a look.


Thanks
ChenYu

Original cover letter from Rob:

This series adds support for CMA/DMA users to skip kernel mappings for
GEM allocations. The DMA API only guarantees a kernel mapping at
allocation time. Creating mappings with vmap() after allocation may or
may not work as not all allocations have a struct page. As virtual
memory space is limited on 32-bit systems some drivers will skip kernel
mappings when possible. This prevents those drivers from using CMA
helpers and the generic fbdev emulation which results in a lot of
duplicated code.

In order to distinguish between kernel and userspace allocations,
a new flag, DRM_MODE_DUMB_KERNEL_MAP, for drm_mode_create_dumb() is
introduced. This allows drivers to override the default behavior for
CMA helpers of always creating a kernel mapping.

Mediatek is converted to CMA helpers and Rockchip is converted to generic
fbdev support. I also have patches to convert Rockchip to CMA and shmem
helpers, but they need a bit more work. Exynos can also probably be
converted to use CMA helpers.

Compile tested only. I did test fbdev on Rockchip, but the h/w I have
has an IOMMU, so the CMA code path doesn't get tested.

- end quote -

[1] https://lore.kernel.org/dri-devel/20191021214550.1461-1-robh@kernel.org/
[2] https://lore.kernel.org/all/20260311094929.3393338-1-wenst@chromium.org/

Rob Herring (3):
  drm: Introduce DRM_MODE_DUMB_KERNEL_MAP flag
  drm/gem-dma: Use the dma_*_attr API variant
  drm/gem-dma: Support DRM_MODE_DUMB_KERNEL_MAP flag

 drivers/gpu/drm/adp/adp_drv.c                 |  1 +
 .../gpu/drm/arm/display/komeda/komeda_kms.c   |  1 +
 drivers/gpu/drm/arm/malidp_drv.c              |  1 +
 drivers/gpu/drm/drm_client.c                  |  2 +
 drivers/gpu/drm/drm_dumb_buffers.c            |  4 +
 drivers/gpu/drm/drm_fb_dma_helper.c           |  4 +
 drivers/gpu/drm/drm_gem_dma_helper.c          | 93 ++++++++++++-------
 drivers/gpu/drm/logicvc/logicvc_drm.c         |  1 +
 drivers/gpu/drm/meson/meson_drv.c             |  1 +
 drivers/gpu/drm/renesas/rcar-du/rcar_du_kms.c |  2 +
 drivers/gpu/drm/renesas/rcar-du/rcar_du_vsp.c |  5 +-
 drivers/gpu/drm/renesas/rz-du/rzg2l_du_kms.c  |  1 +
 drivers/gpu/drm/stm/drv.c                     |  3 +-
 drivers/gpu/drm/sun4i/sun4i_drv.c             |  1 +
 drivers/gpu/drm/vc4/vc4_bo.c                  |  2 +-
 drivers/gpu/drm/vc4/vc4_drv.c                 |  2 +
 drivers/gpu/drm/verisilicon/vs_drm.c          |  2 +
 drivers/gpu/drm/xlnx/zynqmp_kms.c             |  2 +
 include/drm/drm_dumb_buffers.h                |  3 +
 include/drm/drm_gem_dma_helper.h              |  3 +
 20 files changed, 94 insertions(+), 40 deletions(-)

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2.53.0.1018.g2bb0e51243-goog