The current one essentially means you need CMA or a vmalloc backed object, which makes fbdev emulation a special case.

Since implementing this will be quite a bit of work, capture the idea in a TODO.

Cc: Noralf Trønnes noralf@tronnes.org Signed-off-by: Daniel Vetter daniel.vetter@intel.com --- Documentation/gpu/todo.rst | 30 ++++++++++++++++++++++++++++++ 1 file changed, 30 insertions(+)

diff --git a/Documentation/gpu/todo.rst b/Documentation/gpu/todo.rst index 41da7b06195c..0a85dad876ae 100644 --- a/Documentation/gpu/todo.rst +++ b/Documentation/gpu/todo.rst @@ -209,6 +209,36 @@ Would be great to refactor this all into a set of small common helpers.

Contact: Daniel Vetter

+Generic fbdev defio support +--------------------------- + +The defio support code in the fbdev core has some very specific requirements, +which means drivers need to have a special framebuffer for fbdev. Which prevents +us from using the generic fbdev emulation code everywhere. The main issue is +that it uses some fields in struct page itself, which breaks shmem gem objects +(and other things). + +Possible solution would be to write our own defio mmap code in the drm fbdev +emulation. It would need to fully wrap the existing mmap ops, forwarding +everything after it has done the write-protect/mkwrite trickery: + +- In the drm_fbdev_fb_mmap helper, if we need defio, change the + default page prots to write-protected with something like this:: + + vma->vm_page_prot = pgprot_wrprotect(vma->vm_page_prot); + +- Set the mkwrite and fsync callbacks with similar implementions to the core + fbdev defio stuff. These should all work on plain ptes, they don't actually + require a struct page. uff. These should all work on plain ptes, they don't + actually require a struct page. + +- Track the dirty pages in a separate structure (bitfield with one bit per page + should work) to avoid clobbering struct page. + +Might be good to also have some igt testcases for this. + +Contact: Daniel Vetter, Noralf Tronnes + Put a reservation_object into drm_gem_object --------------------------------------------