Re: [PATCH v1 2/2] drivers/gpu/drm: don't select DMA_CMA or CMA from aspeed or etnaviv

On Thu, Apr 8, 2021 at 6:44 PM David Hildenbrand [off-list ref] wrote:

quoted

drivers/gpu/drm/mcde/Kconfig
drivers/gpu/drm/pl111/Kconfig
drivers/gpu/drm/tve200/Kconfig

I was assuming these are "real" dependencies. Will it also work without
DMA_CMA?

It will mostly work but that is only because the reservations are
mostly contiguous anyway because they are done early and
are small. The hardware requires contiguous buffers in all
three cases. I'm not sure I always got it right.

quoted

certainly needs this as well, and pretty much anything that is
selecting DRM_KMS_CMA_HELPER or
DRM_GEM_CMA_HELPER "wants" DMA_CMA.

"wants" as in "desires to use but can life without" or "wants" as in
"really needs it". ?

I don't know the exact semantics of using DRM_KMS_CMA*
without actually using DMA_CMA. I suspect small allocations
will be contiguous and big allocations will start to fragment?
but it's just my guess. I guess "really need it"?

Yours,
Linus Walleij