linux-kernel - [PATCH v3 3/4] drm/vkms: Support setting custom background color

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Message-Id: <20251118-rk3588-bgcolor-v3-3-a2cc909428ea@collabora.com>
Date: Tue, 18 Nov 2025 01:52:01 +0200
From: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
To: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
 Sandy Huang <hjc@...k-chips.com>, 
 Heiko Stübner <heiko@...ech.de>, 
 Andy Yan <andy.yan@...k-chips.com>, 
 Louis Chauvet <louis.chauvet@...tlin.com>, 
 Haneen Mohammed <hamohammed.sa@...il.com>, 
 Melissa Wen <melissa.srw@...il.com>
Cc: Robert Mader <robert.mader@...labora.com>, kernel@...labora.com, 
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
 linux-arm-kernel@...ts.infradead.org, linux-rockchip@...ts.infradead.org
Subject: [PATCH v3 3/4] drm/vkms: Support setting custom background color

Make use of the BACKGROUND_COLOR CRTC property when filling the
background during blending.  It already defaults to solid black.

Since the internal representation of the pixel color in VKMS relies on
16 bits of precision, use the newly introduced DRM_ARGB64_GET{R|G|B}()
helpers to access the individual components of the background color
property, which is compliant with DRM_FORMAT_ARGB16161616.

It's worth noting the alpha component is ignored, hence non-opaque
background colors are not supported.

Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
---
 drivers/gpu/drm/vkms/vkms_composer.c | 10 ++++++++--
 drivers/gpu/drm/vkms/vkms_crtc.c     |  3 +++
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/vkms/vkms_composer.c b/drivers/gpu/drm/vkms/vkms_composer.c
index c1ab12a44621..19e73817bf78 100644
--- a/drivers/gpu/drm/vkms/vkms_composer.c
+++ b/drivers/gpu/drm/vkms/vkms_composer.c
@@ -373,8 +373,14 @@ static void blend(struct vkms_writeback_job *wb,
 {
 	struct vkms_plane_state **plane = crtc_state->active_planes;
 	u32 n_active_planes = crtc_state->num_active_planes;
-
-	const struct pixel_argb_u16 background_color = { .a = 0xffff };
+	u64 bgcolor = crtc_state->base.background_color;
+
+	const struct pixel_argb_u16 background_color = {
+		.a = 0xffff,
+		.r = DRM_ARGB64_GETR(bgcolor),
+		.g = DRM_ARGB64_GETG(bgcolor),
+		.b = DRM_ARGB64_GETB(bgcolor),
+	};
 
 	int crtc_y_limit = crtc_state->base.mode.vdisplay;
 	int crtc_x_limit = crtc_state->base.mode.hdisplay;
diff --git a/drivers/gpu/drm/vkms/vkms_crtc.c b/drivers/gpu/drm/vkms/vkms_crtc.c
index 9a7db1d51022..2514c367f710 100644
--- a/drivers/gpu/drm/vkms/vkms_crtc.c
+++ b/drivers/gpu/drm/vkms/vkms_crtc.c
@@ -4,6 +4,7 @@
 
 #include <drm/drm_atomic.h>
 #include <drm/drm_atomic_helper.h>
+#include <drm/drm_blend.h>
 #include <drm/drm_managed.h>
 #include <drm/drm_print.h>
 #include <drm/drm_probe_helper.h>
@@ -228,6 +229,8 @@ struct vkms_output *vkms_crtc_init(struct drm_device *dev, struct drm_plane *pri
 
 	drm_crtc_enable_color_mgmt(crtc, 0, false, VKMS_LUT_SIZE);
 
+	drm_crtc_attach_background_color_property(crtc);
+
 	spin_lock_init(&vkms_out->lock);
 	spin_lock_init(&vkms_out->composer_lock);
 

-- 
2.51.2