drm: allow limiting the scatter list size.

Add drm_device argument to drm_prime_pages_to_sg(), so we can
call dma_max_mapping_size() to figure the segment size limit
and call into __sg_alloc_table_from_pages() with the correct
limit.

This fixes virtio-gpu with sev.  Possibly it'll fix other bugs
too given that drm seems to totaly ignore segment size limits
so far ...

v2: place max_segment in drm driver not gem object.
v3: move max_segment next to the other gem fields.
v4: just use dma_max_mapping_size().

Signed-off-by: Gerd Hoffmann <[email protected]>
Reviewed-by: Daniel Vetter <[email protected]>
Link: http://patchwork.freedesktop.org/patch/msgid/[email protected]
14 files changed