[RFC PATCH] drm/panfrost: Add support for mapping BOs on GPU page faults

[Chris Wilson]

Quoting Rob Herring (2019-06-10 18:04:40)
> The midgard/bifrost GPUs need to allocate GPU memory which is allocated
> on GPU page faults and not pinned in memory. The vendor driver calls
> this functionality GROW_ON_GPF.
> 
> This implementation assumes that BOs allocated with the
> PANFROST_BO_NOMAP flag are never mmapped or exported. Both of those may
> actually work, but I'm unsure if there's some interaction there. It
> would cause the whole object to be pinned in memory which would defeat
> the point of this.
> 
> Issues/questions/thoughts:
> 
> What's the difference between i_mapping and f_mapping?
> 
> What kind of clean-up on close is needed? Based on vgem faults, there
> doesn't seem to be any refcounting. Assume userspace is responsible for
> not freeing the BO while a page fault can occur?

See drm_gem_vm_open and drm_gem_vm_close.
-Chris