Re: [PATCH 1/3] drm: introduce share plane

[Mark yao]

On 2016å07æ26æ 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@xxxxxxxxxxxxxx>
> 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.

> 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.

> -Daniel

--
ïark Yao