Re: [RFC PATCH v3 0/3] Support for Solid Fill Planes

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Jan 04, 2023 at 03:40:33PM -0800, Jessica Zhang wrote:
> Introduce and add support for a solid_fill property. When the solid_fill
> property is set, and the framebuffer is set to NULL, memory fetch will be
> disabled.
> 
> In addition, loosen the NULL FB checks within the atomic commit callstack
> to allow a NULL FB when the solid_fill property is set and add FB checks
> in methods where the FB was previously assumed to be non-NULL.
> 
> Finally, have the DPU driver use drm_plane_state.solid_fill and instead of
> dpu_plane_state.color_fill, and add extra checks in the DPU atomic commit
> callstack to account for a NULL FB in cases where solid_fill is set.
> 
> Some drivers support hardware that have optimizations for solid fill
> planes. This series aims to expose these capabilities to userspace as
> some compositors have a solid fill flag (ex. SOLID_COLOR in the Android
> hardware composer HAL) that can be set by apps like the Android Gears
> app.
> 
> Userspace can set the solid_fill property to a blob containing the
> appropriate version number and solid fill color (in RGB323232 format) and
> setting the framebuffer to NULL.
> 
> Note: Currently, there's only one version of the solid_fill blob property.
> However if other drivers want to support a similar feature, but require
> more than just the solid fill color, they can extend this feature by
> creating additional versions of the drm_solid_fill struct.
> 
> Changes in V2:
> - Dropped SOLID_FILL_FORMAT property (Simon)
> - Switched to implementing solid_fill property as a blob (Simon, Dmitry)
> - Changed to checks for if solid_fill_blob is set (Dmitry)
> - Abstracted (plane_state && !solid_fill_blob) checks to helper method
>   (Dmitry)
> - Removed DPU_PLANE_COLOR_FILL_FLAG
> - Fixed whitespace and indentation issues (Dmitry)

Now that this is a blob, I do wonder again whether it's not cleaner to set
the blob as the FB pointer. Or create some kind other kind of special data
source objects (because solid fill is by far not the only such thing).

We'd still end up in special cases like when userspace that doesn't
understand solid fill tries to read out such a framebuffer, but these
cases already exist anyway for lack of priviledges.

So I still think that feels like the more consistent way to integrate this
feature. Which doesn't mean it has to happen like that, but the
patches/cover letter should at least explain why we don't do it like this.
-Daniel

> 
> Changes in V3:
> - Fixed some logic errors in atomic checks (Dmitry)
> - Introduced drm_plane_has_visible_data() and drm_atomic_check_fb() helper
>   methods (Dmitry)
> 
> Jessica Zhang (3):
>   drm: Introduce solid fill property for drm plane
>   drm: Adjust atomic checks for solid fill color
>   drm/msm/dpu: Use color_fill property for DPU planes
> 
>  drivers/gpu/drm/drm_atomic.c              | 136 +++++++++++++---------
>  drivers/gpu/drm/drm_atomic_helper.c       |  34 +++---
>  drivers/gpu/drm/drm_atomic_state_helper.c |   9 ++
>  drivers/gpu/drm/drm_atomic_uapi.c         |  59 ++++++++++
>  drivers/gpu/drm/drm_blend.c               |  17 +++
>  drivers/gpu/drm/drm_plane.c               |   8 +-
>  drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c  |   9 +-
>  drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c |  65 +++++++----
>  include/drm/drm_atomic_helper.h           |   5 +-
>  include/drm/drm_blend.h                   |   1 +
>  include/drm/drm_plane.h                   |  62 ++++++++++
>  11 files changed, 302 insertions(+), 103 deletions(-)
> 
> -- 
> 2.38.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch