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[v2,0/4] drm/gem-dma: Support dedicated DMA device for allocation

Message ID 20260311094929.3393338-1-wenst@chromium.org (mailing list archive)
Headers
Series drm/gem-dma: Support dedicated DMA device for allocation |

Message

Chen-Yu Tsai March 11, 2026, 9:49 a.m. UTC 
Hi folks,

This is v2 of my "support dedicated DMA device for allocation and mmap
in GEM DMA helpers" series.

Changes since v1:
- Link to v1: https://lore.kernel.org/all/20260310032511.2545500-1-wenst@chromium.org/
- Collected tags
- Removed reference to mtk_gem.c from the Makefile

This series expands the "dedicated DMA device" support in DRM to the GEM
DMA helpers, and converts the MediaTek DRM driver to setting the DMA
device and dropping the custom GEM helpers that implemented this
function.

Various display drivers implement the "dedicated DMA device" support
with custom GEM helpers. These include Exynos, MediaTek, and Rockchip
to name a few. Allwinner does something entirely different, calling
of_dma_configure() on the virtual display device using the OF node of
the actual DMA device. Recently this causes a warning if IOMMUs are
involved.

The dedicated DMA device is set by calling drm_dev_set_dma_dev(). Any
code that does DMA related actions should use drm_dev_dma_dev() to get
the DMA device. If a dedicated device was not set, then it shall fall
back to the DRM device's underlying device.

This series intends to allow the core helpers to deal with it, and not
have every driver implement it in slightly different ways, duplicating
code.

Patch 1 adds dedicated DMA device support to drm_prime_pages_to_sg().
I believe this was missing from the original change that added dedicated
DMA devices for PRIME.

Patch 2 adds support for dedicated DMA device to the GEM DMA helpers
for GEM buffer allocation and mmap.

Patch 3 converts the MediaTek DRM driver to use the dedicated DMA device
support, and drop all the remaining custom GEM callbacks that deal with
it.

Patch 4 converts the Allwinner sun4i DRM driver to use the dedicated DMA
device support, instead of the of_dma_configure() hack it currently has.

The series should be merged through drm-misc-next so that other drivers
can take advantage of the change.

I also intend to try to convert the Exynos and Rockchip drivers, however
both also have options to set DMA_ATTR_NO_KERNEL_MAPPING when using
dma_alloc_attrs() to allocate memory for the buffers. I intend to
resurrect the DRM_MODE_DUMB_KERNEL_MAP work from Rob Herring [1]
to handle this. The Rockchip driver also has custom IOMMU attachment
that I'm still trying to understand.


Thanks
ChenYu


Chen-Yu Tsai (4):
  drm/prime: Limit scatter list size with dedicated DMA device
  drm/gem-dma: Support dedicated DMA device for allocation and mapping
  drm/mediatek: Set dedicated DMA device and drop custom GEM callbacks
  drm/sun4i: Use backend/mixer as dedicated DMA device

 drivers/gpu/drm/drm_gem_dma_helper.c   |  21 ++-
 drivers/gpu/drm/drm_prime.c            |   2 +-
 drivers/gpu/drm/mediatek/Makefile      |   1 -
 drivers/gpu/drm/mediatek/mtk_crtc.c    |   1 -
 drivers/gpu/drm/mediatek/mtk_drm_drv.c |  21 +--
 drivers/gpu/drm/mediatek/mtk_drm_drv.h |   1 -
 drivers/gpu/drm/mediatek/mtk_gem.c     | 231 -------------------------
 drivers/gpu/drm/mediatek/mtk_gem.h     |  17 --
 drivers/gpu/drm/sun4i/sun4i_backend.c  |  27 +--
 drivers/gpu/drm/sun4i/sun8i_mixer.c    |  27 +--
 10 files changed, 46 insertions(+), 303 deletions(-)
 delete mode 100644 drivers/gpu/drm/mediatek/mtk_gem.c
 delete mode 100644 drivers/gpu/drm/mediatek/mtk_gem.h

Comments

Chen-Yu Tsai March 26, 2026, 6:58 a.m. UTC | #1 
On Wed, 11 Mar 2026 17:49:24 +0800, Chen-Yu Tsai wrote:
> This is v2 of my "support dedicated DMA device for allocation and mmap
> in GEM DMA helpers" series.
> 
> Changes since v1:
> - Link to v1: https://lore.kernel.org/all/20260310032511.2545500-1-wenst@chromium.org/
> - Collected tags
> - Removed reference to mtk_gem.c from the Makefile
> 
> [...]

Applied to drm-misc-next in drm-misc, thanks!

[1/4] drm/prime: Limit scatter list size with dedicated DMA device
      commit: 864279920b2b2c1dd491eba0d0c64764c0c03d9f
[2/4] drm/gem-dma: Support dedicated DMA device for allocation and mapping
      commit: a9da24732aaa80d631bffc8a1390836d4b896690
[3/4] drm/mediatek: Set dedicated DMA device and drop custom GEM callbacks
      commit: e21b1a91430d5ff626a35f72951ed80268e26de6
[4/4] drm/sun4i: Use backend/mixer as dedicated DMA device
      commit: 25e90f486f5bc8f606f4263c9d86e2d2b1db4613

Best regards,