[PATCH 1/3] drm: introduce share plane

[Daniel Vetter]

On Thu, Jul 28, 2016 at 11:01:04AM +0800, Mark yao wrote:
> Any ideas for the share planes?
> 
> This function is important for our series of vop full design.
>     The series of vop is:
>     IP version    chipname
>     3.1           rk3288
>     3.2           rk3368
>     3.4           rk3366
>     3.5           rk3399 big
>     3.6           rk3399 lit
>     3.7           rk322x
> 
> example on rk3288:  if not support share plane, each vop only support four
> planes, but if support this function, each vop can support ten planes.

Like I said, register 10 planes in the kernel driver, figure out a good
way to actually allocate them to hw resources. We have a similar issue on
skl/bxt in the i915 driver where there's only a limited amount of
scalers, and we need to dynamically allocate them to drm_plane. Here you
have fancy amount of scanout engines which you need to dynamically
allocate.

> On 2016年07月26日 17:51, Mark yao wrote:
> > On 2016年07月26日 16:26, Daniel Vetter wrote:
> > > On Tue, Jul 26, 2016 at 03:46:32PM +0800, Mark Yao wrote:
> > > > >What is share plane:
> > > > >Plane hardware only be used when the display scanout run into
> > > > plane active
> > > > >scanout, that means we can reuse the plane hardware resources on plane
> > > > >non-active scanout.
> > > > >
> > > > >      --------------------------------------------------
> > > > >     |  scanout                                       |
> > > > >     |         ------------------                     |
> > > > >     |         | parent plane   |                     |
> > > > >     |         | active scanout |                     |
> > > > >     |         |                |   ----------------- |
> > > > >     |         ------------------   | share plane 1 | |
> > > > >     |  -----------------           |active scanout | |
> > > > >     |  | share plane 0 |           |               | |
> > > > >     |  |active scanout |           ----------------- |
> > > > >     |  |               |                             |
> > > > >     |  -----------------                             |
> > > > >     --------------------------------------------------
> > > > >One plane hardware can be reuse for multi-planes, we assume the first
> > > > >plane is parent plane, other planes share the resource with first one.
> > > > >     parent plane
> > > > >         |---share plane 0
> > > > >         |---share plane 1
> > > > >         ...
> > > > >
> > > > >Because resource share, There are some limit on share plane: one group
> > > > >of share planes need use same zpos, can not overlap, etc.
> > > > >
> > > > >We assume share plane is a universal plane with some limit flags.
> > > > >people who use the share plane need know the limit, should call
> > > > the ioctl
> > > > >DRM_CLIENT_CAP_SHARE_PLANES, and judge the planes limit before use it.
> > > > >
> > > > >A group of share planes would has same shard id, so userspace can
> > > > >group them, judge share plane's limit.
> > > > >
> > > > >Signed-off-by: Mark Yao<mark.yao at rock-chips.com>
> > > This seems extremely hw specific, why exactly do we need to add a new
> > > relationship on planes? What does this buy on_other_  drivers?
> > Yes, now it's plane hardware specific, maybe others have same design,
> > because this design
> > would save hardware resource to support multi-planes.
> > 
> > > Imo this should be solved by virtualizing planes in the driver.
> > > Start out
> > > by assigning planes, and if you can reuse one for sharing then do that,
> > > otherwise allocate a new one. If there's not enough real planes,
> > > fail the
> > > atomic_check.
> > I think that is too complex, trying with atomic_check I think it's not a
> > good idea, userspace try planes every commit would be a heavy work.
> > 
> > Userspace need  know all planes relationship, group them, some display
> > windows can put together, some can't,
> > too many permutation and combination, I think can't just commit with try.
> > 
> > example:
> > userspace:
> > windows 1: pos(0, 0)  size(1024, 100)
> > windows 2: pos(0, 50) size(400, 500)
> > windows 3: pos(0, 200) size(800, 300)
> > 
> > drm plane resources:
> > plane 0 and plane 1 is a group of share planes
> > plane 2 is common plane.
> > 
> > if userspace know the relationship, then they can assign windows 1 and
> > window 3 to plane0 and plane 1. that would be success.
> > but if they don't know, assign window 1/2 to plane 0/1, failed, assign
> > window 2/3 to plane 0/1, failed. mostly would get failed.

You can still do this with the design I describe. The only difference is
that you allow generic userspace to make optimal use of your planes, too.

> > > This seems way to hw specific to be useful as a generic concept.
> > 
> > We want to change the drm_mode_getplane_res behavior, if userspace call
> > DRM_CLIENT_CAP_SHARE_PLANES, that means userspace know hardware limit,
> > then we return full planes support to userspace, if don't, just make a
> > group of share planes as one plane.
> > this work is on generic place.

So ... do you have patches for all the generic kms userspace that's out
there? Are those reviewed and ready for merging?

Adding new userspace abi is much, much, much harder than sovling this in
the vop driver. I'm working on some documentation to make this all clear
(since many arm folks seem unaware of the uapi rules we have in the drm
subsystem). But really, you're trying the much harder route with this
patch.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch