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

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Date:   Tue, 8 Aug 2023 15:57:51 -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 8/7/2023 6:07 PM, Dmitry Baryshkov wrote:
> 
> 
> On 8 August 2023 00:41:07 GMT+03:00, Jessica Zhang <quic_jesszhan@...cinc.com> wrote:
>>
>>
>> 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.
> 
> That depends on the blending mode: in Coverage mode one has independent plane and contents alpha values. And I consider alpha value to be a part of the colour in the rgba/bgra modes.

Acked -- taking Sebastian's concern into consideration, I think I'll 
have "PIXEL_SOURCE_SOLID_FILL_RGB" and add a separate 
"PIXEL_SOURCE_SOLID_FILL_RGBA".

Thanks,

Jessica Zhang

> 
> 
>>
>> Thanks,
>>
>> Jessica Zhang
>>
>>>
>>> -- 
>>> With best wishes
>>> Dmitry
> 
> -- 
> With best wishes
> Dmitry