The backlight level of an eDP panel can be controlled through the AUX channel using DPCD registers of the panel.
The capability for the Source device to adjust backlight characteristics within the panel, using the Sink device DPCD registers is indicated by the TCON_BACKLIGHT_ADJUSTMENT_CAPABLE bit in the EDP_GENERAL_CAPABILITY_1 register (DPCD Address 701h, bit0). In this configuration, the eDP TCON receives the backlight level information from the host, through the AUX channel.
Anderson's patch series [1] exposed the DDC bus from ti-sn65dsi86 bridge, that gives an option to move the backlight control out of the bridge and to create a separate backlight driver.
Changes in v2: - Created a new DisplayPort aux backlight driver and moved the code from drm_dp_aux_backlight.c (v1) to the new driver. - Removed the changes done in ti-sn65dsi86 bridge. (Rob Herring)
[1] https://lore.kernel.org/dri-devel/20210416223950.3586967-1-dianders@chromium...
Rajeev Nandan (2): dt-bindings: backlight: add DisplayPort aux backlight backlight: Add DisplayPort aux backlight driver
.../bindings/leds/backlight/dp-aux-backlight.yaml | 49 +++++ drivers/video/backlight/Kconfig | 7 + drivers/video/backlight/Makefile | 1 + drivers/video/backlight/dp_aux_backlight.c | 245 +++++++++++++++++++++ 4 files changed, 302 insertions(+) create mode 100644 Documentation/devicetree/bindings/leds/backlight/dp-aux-backlight.yaml create mode 100644 drivers/video/backlight/dp_aux_backlight.c