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Subject: Re: [PATCH v3 1/2] drm: Add per-plane pixel blend mode property
To:     Lowry Li <lowry.li@arm.com>,
        Emil Velikov <emil.l.velikov@gmail.com>
Cc:     Liviu Dudau <liviu.dudau@arm.com>,
        Gustavo Padovan <gustavo@padovan.org>,
        "Vetter, Daniel" <daniel.vetter@intel.com>,
        Sean Paul <seanpaul@chromium.org>,
        David Airlie <airlied@linux.ie>,
        =?UTF-8?B?VmlsbGUgU3lyasOkbMOk?= <ville.syrjala@linux.intel.com>,
        ML dri-devel <dri-devel@lists.freedesktop.org>,
        "Linux-Kernel@Vger. Kernel. Org" <linux-kernel@vger.kernel.org>,
        Brian Starkey <brian.starkey@arm.com>,
        Mali DP Maintainers <malidp@foss.arm.com>, nd@arm.com
References: <1527856871-3007-1-git-send-email-lowry.li@arm.com>
 <1527856871-3007-2-git-send-email-lowry.li@arm.com>
 <CACvgo53z9_DLXDXVgsvX6eVRr+-OXuJYu8_q2kANFTgyWCeacQ@mail.gmail.com>
 <20180605090729.GA2686@lowry.li@arm.com>
From:   Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Message-ID: <325674b0-d100-4e38-3963-0e458e6dec80@linux.intel.com>
Date:   Mon, 13 Aug 2018 12:49:13 +0200
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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