[PATCH v5 0/4] Introduce BACKGROUND_COLOR DRM CRTC property

Cristian Ciocaltea
2026-01-27T08:46:01Z

Some display controllers can be hardware-configured to present non-black
colors for pixels which are not covered by any plane (or are exposed
through transparent regions of higher planes).

The 1st patch of the series provides DIV_ROUND_CLOSEST() to uapi, as a
prerequisite to the 2nd patch introducing the BACKGROUND_COLOR DRM
property that can be attached to a CRTC via a dedicated helper function.
A 64-bit ARGB color value format is also defined and can be manipulated
with the help of a few utility macros.

Note this is a reworked version of the patch [1] submitted (many) years
ago by Matt Roper. The main changes are:

* Renamed DRM_ARGB_<COMP>() to DRM_ARGB64_GET<C>_BPC() while providing
convenience wrappers to extract all 16 bits of a specific color via
DRM_ARGB64_GET<C>()
* Replaced drm_argb() function with DRM_ARGB64_PREP_BPC() macro, to
improve uAPI consistency and readability; additionally fixed a bug in
case of using bpc < 16: the unused least-significant bits of a given
component in the output value would contain the unused
most-significant bits of the following component in the input value,
instead of being set to 0
* Replaced GENMASK_ULL(63, 0) with U64_MAX when calling
drm_property_create_range() to create the BACKGROUND_COLOR property
* Moved crtc_state->bgcolor initialization from
__drm_atomic_helper_crtc_reset() to
__drm_atomic_helper_crtc_state_reset()
* Replaced '*bgcolor*' occurrences to '*background_color*' for
consistency with the actual property name in both storage field and
helper functions names

The subsequent patches add background color support to VKMS and the VOP2
display controller used in the RK3568, RK3576, and RK3588 Rockchip SoC
families.

The validation has been done using a dedicated IGT test [2] - see the
reported results below.

On the userland side, a Weston merge request [3] is available, providing
support for the BACKGROUND_COLOR CRTC property to the DRM backend. It
relies on the already existing background-color setting in weston.ini:

[shell]
background-color=0xAARRGGBB

[1] https://lore.kernel.org/all/20190930224707.14904-2-matthew.d.roper@intel.com/
[2] https://lore.kernel.org/all/20251219-crtc-bgcolor-v3-1-31b589911588@collabora.com/
[3] https://gitlab.freedesktop.org/wayland/weston/-/merge_requests/1845

IGT kms_crtc_background_color test results
==========================================

* VKMS

virtme-ng$ IGT_FORCE_DRIVER=vkms build/tests/kms_crtc_background_color

IGT-Version: 2.3-g6b07138e8 (x86_64) (Linux: 6.19.0-rc1-virtme x86_64)
Using IGT_SRANDOM=1766149634 for randomisation
Opened device: /dev/dri/card0
Starting subtest: background-color-red
Starting dynamic subtest: pipe-A-Virtual-1
Dynamic subtest pipe-A-Virtual-1: SUCCESS (0.071s)
Subtest background-color-red: SUCCESS (0.073s)
Starting subtest: background-color-green
Starting dynamic subtest: pipe-A-Virtual-1
Dynamic subtest pipe-A-Virtual-1: SUCCESS (0.074s)
Subtest background-color-green: SUCCESS (0.074s)
Starting subtest: background-color-blue
Starting dynamic subtest: pipe-A-Virtual-1
Dynamic subtest pipe-A-Virtual-1: SUCCESS (0.074s)
Subtest background-color-blue: SUCCESS (0.074s)
Starting subtest: background-color-yellow
Starting dynamic subtest: pipe-A-Virtual-1
Dynamic subtest pipe-A-Virtual-1: SUCCESS (0.072s)
Subtest background-color-yellow: SUCCESS (0.073s)
Starting subtest: background-color-purple
Starting dynamic subtest: pipe-A-Virtual-1
Dynamic subtest pipe-A-Virtual-1: SUCCESS (0.072s)
Subtest background-color-purple: SUCCESS (0.074s)
Starting subtest: background-color-cyan
Starting dynamic subtest: pipe-A-Virtual-1
Dynamic subtest pipe-A-Virtual-1: SUCCESS (0.074s)
Subtest background-color-cyan: SUCCESS (0.074s)
Starting subtest: background-color-black
Starting dynamic subtest: pipe-A-Virtual-1
Dynamic subtest pipe-A-Virtual-1: SUCCESS (0.072s)
Subtest background-color-black: SUCCESS (0.072s)
Starting subtest: background-color-white
Starting dynamic subtest: pipe-A-Virtual-1
Dynamic subtest pipe-A-Virtual-1: SUCCESS (0.073s)
Subtest background-color-white: SUCCESS (0.074s)

* Radxa ROCK 5B (RK3588)

rock5b$ build/tests/kms_crtc_background_color --device drm:/dev/dri/card1

IGT-Version: 2.2-g3e4ec308e (aarch64) (Linux: 6.18.0-rc1 aarch64)
Using IGT_SRANDOM=1762774806 for randomisation
Opened device: /dev/dri/card1
Starting subtest: background-color-red
Starting dynamic subtest: pipe-C-DP-1
Dynamic subtest pipe-C-DP-1: SUCCESS (0.491s)
Subtest background-color-red: SUCCESS (0.493s)
Starting subtest: background-color-green
Starting dynamic subtest: pipe-C-DP-1
Dynamic subtest pipe-C-DP-1: SUCCESS (0.533s)
Subtest background-color-green: SUCCESS (0.535s)
Starting subtest: background-color-blue
Starting dynamic subtest: pipe-C-DP-1
Dynamic subtest pipe-C-DP-1: SUCCESS (0.541s)
Subtest background-color-blue: SUCCESS (0.544s)
Starting subtest: background-color-yellow
Starting dynamic subtest: pipe-C-DP-1
Dynamic subtest pipe-C-DP-1: SUCCESS (0.535s)
Subtest background-color-yellow: SUCCESS (0.537s)
Starting subtest: background-color-purple
Starting dynamic subtest: pipe-C-DP-1
Dynamic subtest pipe-C-DP-1: SUCCESS (0.536s)
Subtest background-color-purple: SUCCESS (0.538s)
Starting subtest: background-color-cyan
Starting dynamic subtest: pipe-C-DP-1
Dynamic subtest pipe-C-DP-1: SUCCESS (0.539s)
Subtest background-color-cyan: SUCCESS (0.541s)
Starting subtest: background-color-black
Starting dynamic subtest: pipe-C-DP-1
(kms_crtc_background_color:744) igt_pipe_crc-WARNING: Warning on condition all_zero in function crc_sanity_checks, file ../lib/igt_pipe_crc.c:475
(kms_crtc_background_color:744) igt_pipe_crc-WARNING: Suspicious CRC: All values are 0.
(kms_crtc_background_color:744) igt_pipe_crc-WARNING: Warning on condition all_zero in function crc_sanity_checks, file ../lib/igt_pipe_crc.c:475
(kms_crtc_background_color:744) igt_pipe_crc-WARNING: Suspicious CRC: All values are 0.
Dynamic subtest pipe-C-DP-1: SUCCESS (0.535s)
Subtest background-color-black: SUCCESS (0.537s)
Starting subtest: background-color-white
Starting dynamic subtest: pipe-C-DP-1
Dynamic subtest pipe-C-DP-1: SUCCESS (0.540s)
Subtest background-color-white: SUCCESS (0.542s)

Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
---
Changes in v5:
- Collected Reviewed-by & Tested-by tags from Nícolas & Diederik
- Dumped background_color prop value in drm_atomic_crtc_print_state()
and updated comment in drm_crtc_state (Nícolas)
- Documented the reasons of not using the DRM_ARGB64_GET*_BPC() helpers
in vop2 related patch (Nícolas)
- Rebased series onto latest drm-misc-next
- Link to v4: https://lore.kernel.org/r/20251219-rk3588-bgcolor-v4-0-2ff1127ea757@collabora.com

Changes in v4:
- Switched to simple bit-shifting approach when performing the bpc
conversion in the vop2 driver, to avoid the expensive division since
we shouldn't be concerned anymore about the precision (Chaoyi)
- Rebased series onto latest drm-misc-next
- Link to v3: https://lore.kernel.org/r/20251118-rk3588-bgcolor-v3-0-a2cc909428ea@collabora.com

Changes in v3:
- Added new patches:
* uapi: Provide DIV_ROUND_CLOSEST()
* drm/vkms: Support setting custom background color
- Improved DRM_ARGB64_{PREP|GET}*() helpers by using a conversion ratio
for better color approximation when dealing with less than 16 bits of
precision
- Mentioned the IGT test in the cover letter while documenting the
validation results; also dropped references to the now useless
modetest wrapper script and its generated report
- Rebased series onto latest drm-misc-next
- Link to v2: https://lore.kernel.org/r/20251013-rk3588-bgcolor-v2-0-25cc3810ba8c@collabora.com

Changes in v2:
- Improved uAPI consistency and readability by introducing
DRM_ARGB64_PREP*() and DRM_ARGB64_GET*() helper macros
- Updated several code comment sections
- Referenced the counterpart Weston support in the cover letter
- Rebased series onto v6.18-rc1
- Link to v1: https://lore.kernel.org/r/20250902-rk3588-bgcolor-v1-0-fd97df91d89f@collabora.com

---
Cristian Ciocaltea (4):
uapi: Provide DIV_ROUND_CLOSEST()
drm: Add CRTC background color property
drm/vkms: Support setting custom background color
drm/rockchip: vop2: Support setting custom background color

drivers/gpu/drm/drm_atomic.c | 1 +
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 +++
drivers/gpu/drm/rockchip/rockchip_drm_vop2.c | 17 ++++++-
drivers/gpu/drm/rockchip/rockchip_drm_vop2.h | 4 ++
drivers/gpu/drm/vkms/vkms_composer.c | 10 ++++-
drivers/gpu/drm/vkms/vkms_crtc.c | 3 ++
include/drm/drm_blend.h | 4 +-
include/drm/drm_crtc.h | 12 +++++
include/drm/drm_mode_config.h | 5 +++
include/linux/math.h | 18 +-------
include/uapi/drm/drm_mode.h | 67 ++++++++++++++++++++++++++++
include/uapi/linux/const.h | 17 +++++++
15 files changed, 183 insertions(+), 25 deletions(-)
---
base-commit: 68e28facbc8ab3e701e1814323d397a75b400865
change-id: 20250829-rk3588-bgcolor-c1a7b9a507bc