At Display Next Hackfest 2026 we reviewed progress moving brightness
control into the DRM connector properties.
There is a range LUMINANCE property that will default to 0->0.
Once a driver attaches a backlight it will be updated to 1->max.
If the panel supports the minimum backlight turning off the display
the range can later be updated to 0->max instead of 1->max.
Version 8 had a lot of review feedback, and the biggest change is that
this no longer has the legacy sysfs interface for brightness control.
There is a Kconfig knob introduced that turns on the new API, and when
the new API is available all drivers will conflict with the old backlight
control API.
This will allow us to land the new brightness control API and the transition
to the new API separately. *This series only tracks the new API itself.*
Here's the main review items that I tried to cover in v8->v9.
- [x] Javier Martinez Canillas: separate generic DRM luminance infrastructure
from the backlight-subsystem adapter; let drivers own the hardware path;
avoid a leaky `drm_backlight_link()` mid-layer.
- [x] Thomas Zimmermann: invoke a connector helper callback from atomic helper
sequencing; keep backlight-specific state in driver-owned structures and
helper code rather than embedding it in DRM core objects.
- [x] Thomas Zimmermann, Leo Li, Harry Wentland: make luminance and display
power/DPMS independent. Preserve requested luminance while a display is
disabled and apply it when the display is enabled.
- [x] Jani Nikula: remove `IS_REACHABLE()` linkage workarounds and express any
remaining dependencies through Kconfig.
- [x] Thomas Zimmermann: remove the driver capability flag if userspace can
discover support by the connector property itself.
- [x] Thomas Zimmermann: remove redundant brightness-change notification and
DRM readback loops when the committed property already contains the
authoritative requested value.
- [x] Maxime Ripard: split the new DRM UAPI from legacy sysfs compatibility so
the property can be reviewed and merged independently.
- [x] Javier Martinez Canillas / Maxime Ripard / Thomas Zimmermann / Xaver Hugl:
preserve legacy sysfs behavior for legacy userspace; avoid silently
breaking the de-facto backlight UAPI while DRM-master ownership is
introduced.
- [x] Harry Wentland / Jani Nikula / Xaver Hugl: terminology reviewed. Retain
`LUMINANCE` as an explicit author decision, while documenting that the
property contains relative, driver-defined levels rather than physical
cd/m^2 values.
As the series changed significantly from all this feedback I did not see value
in a per-patch changelog. Instead here is the changelog from the whole series:
- Reworked the interface around driver-owned connector helper callbacks.
Removed the generic DRM backlight adapter, backend-linking layer, and
backlight state embedded in DRM core objects.
- Made LUMINANCE an atomic connector property whose requested value is
independent of display power. Disable panel emission before shutting down
the pipeline, preserve the requested value while inactive, and apply it
after the pipeline is enabled.
- Removed DRM_CLIENT_CAP_LUMINANCE and the associated per-client takeover,
legacy sysfs inhibition, property visibility, notification, and hardware
readback machinery.
- Removed the kernel-internal backlight API and the backlight notifier
restoration from the series.
- Added the default-off CONFIG_DRM_LUMINANCE option. When disabled, drivers
retain their existing backlight class devices and userspace ABI. When
enabled, all DRM-owned brightness implementations migrate to the connector
property together.
- Migrated AMDGPU, legacy AMD display, i915/Xe, Nouveau, Radeon, GMA500, GUD,
PS8622, SSD130x, panel and bridge connectors, and the DRM MIPI DBI drivers.
- Added common panel, bridge, and MIPI DBI luminance forwarding helpers.
- Retained the LUMINANCE name, while documenting that values are relative,
driver-defined levels rather than physical luminance in cd/m^2.
- Added connector property lifecycle coverage and updated the AMD display
KUnit fixtures for both CONFIG_DRM_LUMINANCE configurations.
- Fixed error propagation when AMD Display Core reads the current brightness
and guarded legacy AMDGPU backlight scratch-register access.
- Restructured the series from 14 to 21 patches splitting the core
infrastructure, shared helpers, and individual driver migrations.
The following compositors have implemented matching support:
* Kwin: https://invent.kde.org/plasma/kwin/-/merge_requests/9298
* Mutter:
https://gitlab.gnome.org/swick/mutter/-/commits/wip/kms-luminance-prop
* Wlroots: https://gitlab.freedesktop.org/wlroots/wlroots/-/merge_requests/5384
I've tested this series using Kwin on amdgpu. I've compile tested other
drivers.
The series is also available on this branch for easy testing.
https://git.kernel.org/pub/scm/linux/kernel/git/superm1/linux.git/log/?h=superm1/backlight-property-v9
And lastly; I've used an LLM to assist with implementing this version,
particularly
on all the drivers I wasn't familiar with.
Assisted-by: LLM
Mario Limonciello (19):
drm: add connector LUMINANCE property
drm/amd/display: Pass up errors reading actual brightness
drm/amd: add luminance property support
drm/i915/display: add luminance property support
drm: add panel and bridge connector luminance forwarding
drm/mipi-dbi: add connector luminance helpers
drm/tiny: migrate panel-mipi-dbi to connector luminance
drm/tiny: migrate HX8357D to connector luminance
drm/tiny: migrate ILI9163 to connector luminance
drm/tiny: migrate ILI9341 to connector luminance
drm/tiny: migrate ILI9486 to connector luminance
drm/tiny: migrate MI0283QT to connector luminance
drm/sitronix: migrate ST7735R to connector luminance
drm/nouveau: add connector luminance support
drm/gud: add connector luminance support
drm/radeon: add connector luminance support
drm/gma500: add connector luminance support
drm/bridge: add PS8622 connector luminance support
drm/solomon: add SSD130x connector luminance support
Mario Limonciello (AMD) (2):
drm/amdgpu: Check bios_scratch_reg_offset in backlight level helper
drm/amd/display: update KUnit luminance fixtures
drivers/gpu/drm/Kconfig | 14 +++
drivers/gpu/drm/amd/amdgpu/Kconfig | 2 +-
drivers/gpu/drm/amd/amdgpu/amdgpu_atombios.c | 7 +-
.../gpu/drm/amd/amdgpu/amdgpu_connectors.c | 20 ++++
.../gpu/drm/amd/amdgpu/atombios_encoders.c | 17 ++-
.../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 22 ++--
.../display/amdgpu_dm/amdgpu_dm_backlight.c | 55 +++++++--
.../display/amdgpu_dm/amdgpu_dm_backlight.h | 4 +-
.../display/amdgpu_dm/amdgpu_dm_connector.c | 7 +-
.../tests/amdgpu_dm_backlight_test.c | 47 ++++++--
.../amdgpu_dm/tests/amdgpu_dm_kunit_helpers.c | 7 +-
drivers/gpu/drm/bridge/Kconfig | 2 +-
drivers/gpu/drm/bridge/panel.c | 39 +++++++
drivers/gpu/drm/bridge/parade-ps8622.c | 45 +++++--
.../gpu/drm/display/drm_bridge_connector.c | 65 +++++++++++
drivers/gpu/drm/drm_atomic_helper.c | 73 +++++++++++-
drivers/gpu/drm/drm_atomic_state_helper.c | 7 ++
drivers/gpu/drm/drm_atomic_uapi.c | 5 +
drivers/gpu/drm/drm_connector.c | 57 +++++++++
drivers/gpu/drm/drm_mipi_dbi.c | 36 ++++++
drivers/gpu/drm/drm_panel.c | 55 +++++++++
drivers/gpu/drm/gma500/Kconfig | 2 +-
drivers/gpu/drm/gma500/backlight.c | 45 ++++---
drivers/gpu/drm/gma500/cdv_intel_lvds.c | 2 +
drivers/gpu/drm/gma500/psb_drv.c | 2 +-
drivers/gpu/drm/gma500/psb_drv.h | 4 +-
drivers/gpu/drm/gma500/psb_intel_lvds.c | 3 +-
drivers/gpu/drm/gud/Kconfig | 2 +-
drivers/gpu/drm/gud/gud_connector.c | 48 +++++++-
drivers/gpu/drm/i915/Kconfig | 2 +-
drivers/gpu/drm/i915/display/icl_dsi.c | 1 +
.../gpu/drm/i915/display/intel_backlight.c | 20 ++++
.../gpu/drm/i915/display/intel_backlight.h | 1 +
drivers/gpu/drm/i915/display/intel_display.c | 2 +
drivers/gpu/drm/i915/display/intel_dp.c | 1 +
drivers/gpu/drm/i915/display/intel_lvds.c | 1 +
drivers/gpu/drm/i915/display/intel_panel.c | 8 +-
drivers/gpu/drm/i915/display/vlv_dsi.c | 1 +
drivers/gpu/drm/nouveau/Kconfig | 4 +-
drivers/gpu/drm/nouveau/dispnv50/disp.c | 2 +-
drivers/gpu/drm/nouveau/nouveau_backlight.c | 110 ++++++++++++++----
drivers/gpu/drm/nouveau/nouveau_connector.c | 2 +
drivers/gpu/drm/nouveau/nouveau_connector.h | 14 +++
drivers/gpu/drm/radeon/Kconfig | 2 +-
drivers/gpu/drm/radeon/atombios_encoders.c | 32 ++++-
drivers/gpu/drm/radeon/radeon_connectors.c | 34 ++++++
.../gpu/drm/radeon/radeon_legacy_encoders.c | 49 ++++++--
drivers/gpu/drm/radeon/radeon_mode.h | 2 +
drivers/gpu/drm/sitronix/Kconfig | 2 +-
drivers/gpu/drm/sitronix/st7735r.c | 3 +
drivers/gpu/drm/solomon/Kconfig | 2 +-
drivers/gpu/drm/solomon/ssd130x.c | 79 ++++++++++---
drivers/gpu/drm/tests/drm_connector_test.c | 28 +++++
drivers/gpu/drm/tiny/Kconfig | 12 +-
drivers/gpu/drm/tiny/hx8357d.c | 3 +
drivers/gpu/drm/tiny/ili9163.c | 3 +
drivers/gpu/drm/tiny/ili9341.c | 3 +
drivers/gpu/drm/tiny/ili9486.c | 3 +
drivers/gpu/drm/tiny/mi0283qt.c | 3 +
drivers/gpu/drm/tiny/panel-mipi-dbi.c | 3 +
drivers/gpu/drm/xe/Kconfig | 2 +-
include/drm/drm_atomic_helper.h | 3 +
include/drm/drm_bridge.h | 26 +++++
include/drm/drm_connector.h | 16 +++
include/drm/drm_mipi_dbi.h | 7 +-
include/drm/drm_modeset_helper_vtables.h | 25 ++++
include/drm/drm_panel.h | 5 +
67 files changed, 1070 insertions(+), 140 deletions(-)
--
2.43.0
