Partially refactor mtk_gem to stop using (and remove) the unneeded
custom mtk_gem_obj structure and migrate drivers to use the API
defined drm_gem_dma_object structure instead, and to align all of
the functions to be similar to the logic from drm_gem_dma_helper.
Unfortunately, for this driver it wasn't possible to directly use
the drm_gem_dma_helper callbacks (apart from .print_info), as the
DMA mapping here is done on specific dma devices instead of the
main DRM device.
Also, since the mtk_gem_obj structure is no more, also migrate the
mtk_plane.c code to grab the DMA address from a drm_gem_dma_object
and replace the inclusion of the custom mtk_gem.h header (as it is
now unneeded) with the DRM API provided drm_gem_dma_helper.
While at it, also set DRM_GEM_DMA_HELPER as an unconditional
dependency (remove the `if DRM_FBDEV_EMULATION` from the select
DRM_GEM_DMA_HELPER statement in Kconfig).
This resolves an issue pointed by UBSAN, as when using drm_fbdev_dma
the drm_gem_object is supposed to be child of a drm_gem_dma_object
instead of a custom mtk_gem_obj (or the mtk_gem_obj should have been
reordered to have the same fields as drm_gem_dma_object, but that
would have been too fragile and generally a bad idea anyway).
Fixes: 0992284b4fe4 ("drm/mediatek: Use fbdev-dma")
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20251111085114.9752-1-angelogioacchino.delregno@collabora.com/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>