Re: [PATCH v2 2/4] drm/gem-dma: Support dedicated DMA device for allocation and mapping

[AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>]

Il 11/03/26 10:49, Chen-Yu Tsai ha scritto:
> Support for a dedicated DMA device for prime imports was added in commit
> 143ec8d3f939 ("drm/prime: Support dedicated DMA device for dma-buf imports").
> This allowed the DRM driver to provide a dedicated DMA device when its
> own underlying device was not capable of DMA, for example when it is a
> USB device (the original target) or a virtual device. The latter case is
> common on embedded SoCs, on which the display pipeline is composed of
> various fixed function blocks, and the DRM device is simply a made-up
> device, an address space managing the routing between the blocks, or
> whichever block the implementor thought made sense at the time. The
> point is that the chosen device is often not the actual device doing
> the DMA. Various drivers have used workarounds or reimplemented the
> GEM DMA helpers to get the DMA addresses and IOMMUs to work correctly.
> 
> Add support for the dedicated DMA device to the GEM DMA helpers.
> 
> No existing driver currently uses the GEM DMA helpers and calls
> drm_dev_set_dma_dev() to set a dedicated DMA device, so no existing
> users should be affected.
> 
> Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
> Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>