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

From: Mark yao
Date: Tue Jul 26 2016 - 05:52:11 EST

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
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.

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.


ïark Yao