Re: [PATCH RESEND 0/4] drm/gem-dma: Support dedicated DMA device for allocation

[Thomas Zimmermann <tzimmermann@suse.de>]

Hi

Am 10.03.26 um 04:25 schrieb Chen-Yu Tsai:
> (resent with Samuel's email address fixed)
>
> Hi folks,
>
> 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.

I wanted to do this myself at some point. So thanks a lot for picking up 
the task. Happy to see this series.

>
> 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.
>
> 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.

We originally added the dedicated DMA device for supporting PRIME on USB 
graphics adapters, where the DMA buffer has to be allocated wrt to the 
USB controller. We left out anything that wasn't necessary.

>
> 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.

Yes.

Best regards
Thomas

>
> 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/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 +--
>   9 files changed, 46 insertions(+), 302 deletions(-)
>   delete mode 100644 drivers/gpu/drm/mediatek/mtk_gem.c
>   delete mode 100644 drivers/gpu/drm/mediatek/mtk_gem.h
>

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)