* [PATCH] drm/todo: Better defio support in the generic fbdev emulation
@ 2019-01-07 10:22 Daniel Vetter
2019-01-07 16:43 ` Noralf Trønnes
0 siblings, 1 reply; 3+ messages in thread
From: Daniel Vetter @ 2019-01-07 10:22 UTC (permalink / raw)
To: DRI Development; +Cc: Daniel Vetter, Daniel Vetter
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
--------------------------------------------
--
2.20.0.rc1
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^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] drm/todo: Better defio support in the generic fbdev emulation
2019-01-07 10:22 [PATCH] drm/todo: Better defio support in the generic fbdev emulation Daniel Vetter
@ 2019-01-07 16:43 ` Noralf Trønnes
2019-01-08 8:03 ` Daniel Vetter
0 siblings, 1 reply; 3+ messages in thread
From: Noralf Trønnes @ 2019-01-07 16:43 UTC (permalink / raw)
To: Daniel Vetter, DRI Development; +Cc: Daniel Vetter
Den 07.01.2019 11.22, skrev Daniel Vetter:
> 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>
> ---
Acked-by: Noralf Trønnes <noralf@tronnes.org>
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] drm/todo: Better defio support in the generic fbdev emulation
2019-01-07 16:43 ` Noralf Trønnes
@ 2019-01-08 8:03 ` Daniel Vetter
0 siblings, 0 replies; 3+ messages in thread
From: Daniel Vetter @ 2019-01-08 8:03 UTC (permalink / raw)
To: Noralf Trønnes; +Cc: Daniel Vetter, DRI Development, Daniel Vetter
On Mon, Jan 07, 2019 at 05:43:22PM +0100, Noralf Trønnes wrote:
> Den 07.01.2019 11.22, skrev Daniel Vetter:
> > 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>
> > ---
>
> Acked-by: Noralf Trønnes <noralf@tronnes.org>
Thanks for taking a look, pushed to drm-misc-next.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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2019-01-07 10:22 [PATCH] drm/todo: Better defio support in the generic fbdev emulation Daniel Vetter
2019-01-07 16:43 ` Noralf Trønnes
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