linux-kernel - Re: [PATCH v4 2/4] drm: Add CRTC background color property

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Message-ID: <e5177fe1-2ee1-465e-809d-92233efa2095@collabora.com>
Date: Tue, 27 Jan 2026 11:01:05 +0200
From: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
To: Nícolas F. R. A. Prado <nfraprado@...labora.com>,
 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,
 Matt Roper <matthew.d.roper@...el.com>
Subject: Re: [PATCH v4 2/4] drm: Add CRTC background color property

On 1/26/26 8:23 PM, Nícolas F. R. A. Prado wrote:
> On Fri, 2025-12-19 at 23:46 +0200, Cristian Ciocaltea wrote:
>> Some display controllers can be hardware programmed to show non-black
>> colors for pixels that are either not covered by any plane or are
>> exposed through transparent regions of higher planes.  This feature
>> can
>> help reduce memory bandwidth usage, e.g. in compositors managing a UI
>> with a solid background color while using smaller planes to render
>> the
>> remaining content.
>>
>> To support this capability, introduce the BACKGROUND_COLOR standard
>> DRM
>> mode property, which can be attached to a CRTC through the
>> drm_crtc_attach_background_color_property() helper function.
>>
>> Additionally, define a 64-bit ARGB format value to be built with the
>> help of a couple of dedicated DRM_ARGB64_PREP*() helpers.  Individual
>> color components can be extracted with desired precision using the
>> corresponding DRM_ARGB64_GET*() macros.
>>
>> Co-developed-by: Matt Roper <matthew.d.roper@...el.com>
>> Signed-off-by: Matt Roper <matthew.d.roper@...el.com>
>> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
>> ---
>>  drivers/gpu/drm/drm_atomic_state_helper.c |  1 +
>>  drivers/gpu/drm/drm_atomic_uapi.c         |  4 ++
>>  drivers/gpu/drm/drm_blend.c               | 39 ++++++++++++++++--
>>  drivers/gpu/drm/drm_mode_config.c         |  6 +++
>>  include/drm/drm_blend.h                   |  4 +-
>>  include/drm/drm_crtc.h                    | 12 ++++++
>>  include/drm/drm_mode_config.h             |  5 +++
>>  include/uapi/drm/drm_mode.h               | 67
>> +++++++++++++++++++++++++++++++
>>  8 files changed, 133 insertions(+), 5 deletions(-)
> 
> You should also add a dump for this property in
> drm_atomic_crtc_print_state().

This and all your other comments have been addressed in v5 [1].

$ grep background_color -B13 /sys/kernel/debug/dri/display-subsystem/state
crtc[82]: video_port0
	enable=1
	active=1
	self_refresh_active=0
	planes_changed=1
	mode_changed=0
	active_changed=0
	connectors_changed=0
	color_mgmt_changed=0
	plane_mask=1
	connector_mask=1
	encoder_mask=1
	mode: "3840x2160": 60 594000 3840 4016 4104 4400 2160 2168 2178 2250 0x48 0x9
	background_color=ffff000000000000

Thanks,
Cristian

[1] https://lore.kernel.org/all/20260127-rk3588-bgcolor-v5-0-b25aa8613211@collabora.com/