linux-kernel - Re: [PATCH RFC v5 02/10] drm: Introduce solid fill DRM plane property

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Date:   Mon, 7 Aug 2023 14:41:07 -0700
From:   Jessica Zhang <quic_jesszhan@...cinc.com>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
CC:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        <quic_abhinavk@...cinc.com>, <ppaalanen@...il.com>,
        <contact@...rsion.fr>, <laurent.pinchart@...asonboard.com>,
        <sebastian.wick@...hat.com>, <ville.syrjala@...ux.intel.com>,
        <dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-msm@...r.kernel.org>, <freedreno@...ts.freedesktop.org>,
        <wayland-devel@...ts.freedesktop.org>
Subject: Re: [PATCH RFC v5 02/10] drm: Introduce solid fill DRM plane property



On 8/4/2023 6:27 AM, Dmitry Baryshkov wrote:
> On Fri, 28 Jul 2023 at 20:03, Jessica Zhang <quic_jesszhan@...cinc.com> wrote:
>>
>> Document and add support for solid_fill property to drm_plane. In
>> addition, add support for setting and getting the values for solid_fill.
>>
>> To enable solid fill planes, userspace must assign a property blob to
>> the "solid_fill" plane property containing the following information:
>>
>> struct drm_mode_solid_fill {
>>          u32 version;
>>          u32 r, g, b;
>> };
>>
>> Signed-off-by: Jessica Zhang <quic_jesszhan@...cinc.com>
>> ---
>>   drivers/gpu/drm/drm_atomic_state_helper.c |  9 +++++
>>   drivers/gpu/drm/drm_atomic_uapi.c         | 55 +++++++++++++++++++++++++++++++
>>   drivers/gpu/drm/drm_blend.c               | 30 +++++++++++++++++
>>   include/drm/drm_blend.h                   |  1 +
>>   include/drm/drm_plane.h                   | 35 ++++++++++++++++++++
>>   include/uapi/drm/drm_mode.h               | 24 ++++++++++++++
>>   6 files changed, 154 insertions(+)
>>
> 
> [skipped most of the patch]
> 
>> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
>> index 43691058d28f..53c8efa5ad7f 100644
>> --- a/include/uapi/drm/drm_mode.h
>> +++ b/include/uapi/drm/drm_mode.h
>> @@ -259,6 +259,30 @@ struct drm_mode_modeinfo {
>>          char name[DRM_DISPLAY_MODE_LEN];
>>   };
>>
>> +/**
>> + * struct drm_mode_solid_fill - User info for solid fill planes
>> + *
>> + * This is the userspace API solid fill information structure.
>> + *
>> + * Userspace can enable solid fill planes by assigning the plane "solid_fill"
>> + * property to a blob containing a single drm_mode_solid_fill struct populated with an RGB323232
>> + * color and setting the pixel source to "SOLID_FILL".
>> + *
>> + * For information on the plane property, see drm_plane_create_solid_fill_property()
>> + *
>> + * @version: Version of the blob. Currently, there is only support for version == 1
>> + * @r: Red color value of single pixel
>> + * @g: Green color value of single pixel
>> + * @b: Blue color value of single pixel
>> + */
>> +struct drm_mode_solid_fill {
>> +       __u32 version;
>> +       __u32 r;
>> +       __u32 g;
>> +       __u32 b;
> 
> Another thought about the drm_mode_solid_fill uABI. I still think we
> should add alpha here. The reason is the following:
> 
> It is true that we have  drm_plane_state::alpha and the plane's
> "alpha" property. However it is documented as "the plane-wide opacity
> [...] It can be combined with pixel alpha. The pixel values in the
> framebuffers are expected to not be pre-multiplied by the global alpha
> associated to the plane.".
> 
> I can imagine a use case, when a user might want to enable plane-wide
> opacity, set "pixel blend mode" to "Coverage" and then switch between
> partially opaque framebuffer and partially opaque solid-fill without
> touching the plane's alpha value.

Hi Dmitry,

I don't really agree that adding a solid fill alpha would be a good 
idea. Since the intent behind solid fill is to have a single color for 
the entire plane, I think it makes more sense to have solid fill rely on 
the global plane alpha.

As stated in earlier discussions, I think having both a solid_fill.alpha 
and a plane_state.alpha would be redundant and serve to confuse the user 
as to which one to set.

Thanks,

Jessica Zhang

> 
> -- 
> With best wishes
> Dmitry