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drm/todo: Clarify situation around fbdev and defio

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The TODO item is misleading and makes it seem as if fbdev emulation
cannot be used with SHMEM. Rephrase the text to describe the current
situation more correctly.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Noralf Trønnes <noralf@tronnes.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191025092759.13069-3-tzimmermann@suse.de
This commit is contained in:
Thomas Zimmermann 2019-10-25 11:27:59 +02:00
parent 8e86dee022
commit 955a72cea5
1 changed files with 4 additions and 4 deletions
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8
Documentation/gpu/todo.rst
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@ -206,10 +206,10 @@ 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).
which means drivers need to have a special framebuffer for fbdev. The main
issue is that it uses some fields in struct page itself, which breaks shmem
gem objects (and other things). To support defio, affected drivers require
the use of a shadow buffer, which may add CPU and memory overhead.
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