Re: [PATCH v3 1/2] drm: Add per-plane pixel blend mode property

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Aug 14, 2018 at 11:15:43AM +0200, Maarten Lankhorst wrote:
> Op 14-08-18 om 05:11 schreef Lowry Li:
> > On Mon, Aug 13, 2018 at 12:49:13PM +0200, Maarten Lankhorst wrote:
> >> Op 05-06-18 om 11:07 schreef Lowry Li:
> >>> On Mon, Jun 04, 2018 at 02:49:26PM +0100, Emil Velikov wrote:
> >>>> On 1 June 2018 at 13:41, Lowry Li <lowry.li@arm.com> wrote:
> >>>>> Pixel blend modes represent the alpha blending equation
> >>>>> selection, describing how the pixels from the current
> >>>>> plane are composited with the background.
> >>>>>
> >>>>> Add a pixel_blend_mode to drm_plane_state and a
> >>>>> blend_mode_property to drm_plane, and related support
> >>>>> functions.
> >>>>>
> >>>>> Defines three blend modes in drm_blend.h.
> >>>>>
> >>>>> Signed-off-by: Lowry Li <lowry.li@arm.com>
> >>>>> ---
> >>>>>  drivers/gpu/drm/drm_atomic.c        |   4 ++
> >>>>>  drivers/gpu/drm/drm_atomic_helper.c |   1 +
> >>>>>  drivers/gpu/drm/drm_blend.c         | 126 ++++++++++++++++++++++++++++++++++++
> >>>>>  include/drm/drm_blend.h             |   6 ++
> >>>>>  include/drm/drm_plane.h             |   5 ++
> >>>>>  5 files changed, 142 insertions(+)
> >>>>>
> >>>>> diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> >>>>> index 07fef42..1d18389 100644
> >>>>> --- a/drivers/gpu/drm/drm_atomic.c
> >>>>> +++ b/drivers/gpu/drm/drm_atomic.c
> >>>>> @@ -785,6 +785,8 @@ static int drm_atomic_plane_set_property(struct drm_plane *plane,
> >>>>>                 state->src_h = val;
> >>>>>         } else if (property == plane->alpha_property) {
> >>>>>                 state->alpha = val;
> >>>>> +       } else if (property == plane->blend_mode_property) {
> >>>>> +               state->pixel_blend_mode = val;
> >>>>>         } else if (property == plane->rotation_property) {
> >>>>>                 if (!is_power_of_2(val & DRM_MODE_ROTATE_MASK))
> >>>>>                         return -EINVAL;
> >>>>> @@ -852,6 +854,8 @@ static int drm_atomic_plane_set_property(struct drm_plane *plane,
> >>>>>                 *val = state->src_h;
> >>>>>         } else if (property == plane->alpha_property) {
> >>>>>                 *val = state->alpha;
> >>>>> +       } else if (property == plane->blend_mode_property) {
> >>>>> +               *val = state->pixel_blend_mode;
> >>>>>         } else if (property == plane->rotation_property) {
> >>>>>                 *val = state->rotation;
> >>>>>         } else if (property == plane->zpos_property) {
> >>>>> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> >>>>> index 130da51..7f5d463 100644
> >>>>> --- a/drivers/gpu/drm/drm_atomic_helper.c
> >>>>> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> >>>>> @@ -3515,6 +3515,7 @@ void drm_atomic_helper_plane_reset(struct drm_plane *plane)
> >>>>>                 /* Reset the alpha value to fully opaque if it matters */
> >>>>>                 if (plane->alpha_property)
> >>>>>                         plane->state->alpha = plane->alpha_property->values[1];
> >>>>> +               plane->state->pixel_blend_mode = DRM_MODE_BLEND_PREMULTI;
> >>>>>         }
> >>>>>  }
> >>>>>  EXPORT_SYMBOL(drm_atomic_helper_plane_reset);
> >>>>> diff --git a/drivers/gpu/drm/drm_blend.c b/drivers/gpu/drm/drm_blend.c
> >>>>> index a16a74d..ac6f19c 100644
> >>>>> --- a/drivers/gpu/drm/drm_blend.c
> >>>>> +++ b/drivers/gpu/drm/drm_blend.c
> >>>>> @@ -107,6 +107,52 @@
> >>>>>   *     planes. Without this property the primary plane is always below the cursor
> >>>>>   *     plane, and ordering between all other planes is undefined.
> >>>>>   *
> >>>>> + * pixel blend mode:
> >>>>> + *     Pixel blend mode is set up with drm_plane_create_blend_mode_property().
> >>>>> + *     It adds a blend mode for alpha blending equation selection, describing
> >>>>> + *     how the pixels from the current plane are composited with the
> >>>>> + *     background.
> >>>>> + *
> >>>>> + *      Three alpha blending equations are defined:
> >>>>> + *
> >>>>> + *      "None":
> >>>>> + *              Blend formula that ignores the pixel alpha::
> >>>>> + *
> >>>>> + *                      out.rgb = plane_alpha * fg.rgb +
> >>>>> + *                              (1 - plane_alpha) * bg.rgb
> >>>>> + *
> >>>>> + *      "Pre-multiplied":
> >>>>> + *              Blend formula that assumes the pixel color values
> >>>>> + *              have been already pre-multiplied with the alpha
> >>>>> + *              channel values::
> >>>>> + *
> >>>>> + *                      out.rgb = plane_alpha * fg.rgb +
> >>>>> + *                              (1 - (plane_alpha * fg.alpha)) * bg.rgb
> >>>>> + *
> >>>>> + *      "Coverage":
> >>>>> + *              Blend formula that assumes the pixel color values have not
> >>>>> + *              been pre-multiplied and will do so when blending them to the
> >>>>> + *              background color values::
> >>>>> + *
> >>>>> + *                      out.rgb = plane_alpha * fg.alpha * fg.rgb +
> >>>>> + *                              (1 - (plane_alpha * fg.alpha)) * bg.rgb
> >>>>> + *
> >>>>> + *      Using the following symbols:
> >>>>> + *
> >>>>> + *      ``fg.rgb``:
> >>>>> + *              Each of the RGB component values from the plane's pixel
> >>>>> + *      ``fg.alpha``:
> >>>>> + *              Alpha component value from the plane's pixel. If the plane's
> >>>>> + *              pixel format has no alpha component, then this is assumed to be
> >>>>> + *              1.0. In these cases, this property has no effect, as all three
> >>>>> + *              equations become equivalent.
> >>>>> + *      ``bg.rgb``:
> >>>>> + *              Each of the RGB component values from the background
> >>>>> + *      ``plane_alpha``:
> >>>>> + *              Plane alpha value set by the plane "alpha" property. If the
> >>>>> + *              plane does not expose the "alpha" property, then this is
> >>>>> + *              assumed to be 1.0
> >>>>> + *
> >>>>>   * Note that all the property extensions described here apply either to the
> >>>>>   * plane or the CRTC (e.g. for the background color, which currently is not
> >>>>>   * exposed and assumed to be black).
> >>>>> @@ -448,3 +494,83 @@ int drm_atomic_normalize_zpos(struct drm_device *dev,
> >>>>>         return 0;
> >>>>>  }
> >>>>>  EXPORT_SYMBOL(drm_atomic_normalize_zpos);
> >>>>> +
> >>>>> +/**
> >>>>> + * drm_plane_create_blend_mode_property - create a new blend mode property
> >>>>> + * @plane: drm plane
> >>>>> + * @supported_modes: bitmask of supported modes, must include
> >>>>> + *                  BIT(DRM_MODE_BLEND_PREMULTI). Current DRM assumption is
> >>>>> + *                  that alpha is premultiplied, and old userspace can break if
> >>>>> + *                  the property defaults to coverage.
> >>>>> + *
> >>>> Thanks for the explanation Lowry.
> >>>> Sigh, old userspace :-\
> >>>>
> >>>> One pedantic suggestion s/defaults to coverage/defaults to anything else/
> >>>> Since defaulting to "none" or any future blend mode is also a no-go.
> >>>>
> >>>> I wouldn't bother resending solely for ^^. Perhaps squash locally
> >>>> before merging?
> >>>>
> >>>> With that, the patch is
> >>>> Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
> >>>>
> >>>> -Emil
> >>> Hi Emil,
> >>>
> >>> Thanks a lot for your review and will change that.
> >> Ping? Any updates?
> >>
> >> ~Maarten
> > Hi Maarten,
> >
> > So far the merge request on user space patch has been verified by John
> > Stultz. The comments from Sean has been fixed and now we are waiting the
> > reviewed-tag from Sean. Once it merged, we'll send a new kernel patch to
> > review.
> >
> Hey,
> 
> In general the kernel patch should be merged first, because userspace cannot rely on the behavior until the next -rc1 that integrates it.
> However, in order to merge the kernel patch, a userspace proof of concept for validation is needed first. Since you're close to merging,
> I would say the userspace requirement is satisfied. It's safe to send the kernel patch. :)

Quick correction: Generally merged into -next is considered good enough.
-Daniel

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