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

From: Jessica Zhang
Date: Mon Aug 07 2023 - 17:41:51 EST




On 8/4/2023 6:27 AM, Dmitry Baryshkov wrote:
On Fri, 28 Jul 2023 at 20:03, Jessica Zhang <quic_jesszhan@xxxxxxxxxxx> 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@xxxxxxxxxxx>
---
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