[Intel-gfx] [PATCH] drm-buf: Add debug option

Chris Wilson chris at chris-wilson.co.uk
Thu Jan 14 09:45:37 UTC 2021

Quoting Daniel Vetter (2021-01-14 09:30:32)
> On Thu, Jan 14, 2021 at 10:23 AM Chris Wilson <chris at chris-wilson.co.uk> wrote:
> > The only other problem I see with the implementation is that there's
> > nothing that says that each dmabuf->ops->map_dma_buf() returns a new
> > sg_table, so we may end up undoing the xor. Or should each dma-buf
> > return a fresh dma-mapping for iommu isolation?
> Maybe I screwed it up, but that's why I extracted the little helpers:
> We scramble when we get the sgtable from exporter, and unscramble
> before we pass it back. dma-buf.c does some caching and will hand back
> the same sgtable, but for that case we don't re-scramble.

The attachment is only mapped once, but there can be more than one
attachment, and the backend could return the same sg_table for each
mapping. Conceivably, it could return its own private sg_table where it
wants to maintain the struct page. Seems like just adding a sentence to
@map_dma_buf to clarify that each call should return a new sg_table will

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