On 1/12/26 9:28 AM, Vivek Das Mohapatra wrote:
Internal backlight levels are initialised from ACPI but the values are sometimes out of sync with the levels in effect until there has been a read from hardware (eg triggered by reading from sysfs).This means that the first drm_commit can cause the levels to be set to a different value than the actual starting one, which results in a sudden change in brightness. This path shows the problem (when the values are out of sync): amdgpu_dm_atomic_commit_tail() -> amdgpu_dm_commit_streams() -> amdgpu_dm_backlight_set_level(..., dm->brightness[n]) This patch calls the backlight ops get_brightness explicitly at the end of backlight registration to make sure dm->brightness[n] is in sync with the actual hardware levels. Signed-off-by: Vivek Das Mohapatra <[email protected]>
Reviewed-by: Mario Limonciello (AMD) <[email protected]>
--- .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c index 354e359c4507..9e8cbfeee915 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c @@ -5258,6 +5258,8 @@ amdgpu_dm_register_backlight_device(struct amdgpu_dm_connector *aconnector) struct amdgpu_dm_backlight_caps *caps; char bl_name[16]; int min, max; + int real_brightness; + int init_brightness;if (aconnector->bl_idx == -1)return; @@ -5282,6 +5284,8 @@ amdgpu_dm_register_backlight_device(struct amdgpu_dm_connector *aconnector) } else props.brightness = props.max_brightness = MAX_BACKLIGHT_LEVEL;+ init_brightness = props.brightness;+ if (caps->data_points && !(amdgpu_dc_debug_mask & DC_DISABLE_CUSTOM_BRIGHTNESS_CURVE)) { drm_info(drm, "Using custom brightness curve\n"); props.scale = BACKLIGHT_SCALE_NON_LINEAR; @@ -5300,8 +5304,20 @@ amdgpu_dm_register_backlight_device(struct amdgpu_dm_connector *aconnector) if (IS_ERR(dm->backlight_dev[aconnector->bl_idx])) { drm_err(drm, "DM: Backlight registration failed!\n"); dm->backlight_dev[aconnector->bl_idx] = NULL; - } else + } else { + /* + * dm->brightness[x] can be inconsistent just after startup until + * ops.get_brightness is called. + */ + real_brightness = + amdgpu_dm_backlight_ops.get_brightness(dm->backlight_dev[aconnector->bl_idx]); + + if (real_brightness != init_brightness) { + dm->actual_brightness[aconnector->bl_idx] = real_brightness; + dm->brightness[aconnector->bl_idx] = real_brightness; + } drm_dbg_driver(drm, "DM: Registered Backlight device: %s\n", bl_name); + } }static int initialize_plane(struct amdgpu_display_manager *dm,
