If a display supports backlight control using the nouveau driver, and also supports standard ACPI backlight control, there will be two sets of controls.
/sys/class/backlight/acpi_video0 /sys/class/backlight/nv_backlight
This creates ambiguity because these controls can be out of sync with each other. One could be at 100% while the other is at 0% and the actual display brightness depends on which one was used last. This also creates anomalies in Powertop which will show two values for brightness with potentially different values.
Fix this ambiguity by having the nouveau driver only enable its backlight controls if the standard ACPI controls are not present.
Signed-off-by: Jeremiah Mahler jmmahler@gmail.com --- drivers/gpu/drm/nouveau/nouveau_backlight.c | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/drivers/gpu/drm/nouveau/nouveau_backlight.c b/drivers/gpu/drm/nouveau/nouveau_backlight.c index e566c5b..3a52bd4 100644 --- a/drivers/gpu/drm/nouveau/nouveau_backlight.c +++ b/drivers/gpu/drm/nouveau/nouveau_backlight.c @@ -221,6 +221,11 @@ nouveau_backlight_init(struct drm_device *dev) struct nvif_device *device = &drm->device; struct drm_connector *connector;
+ if (acpi_video_backlight_support()) { + dev_info(dev->dev, "Standard ACPI backlight control supported, disabling local control.\n"); + return 0; + } + list_for_each_entry(connector, &dev->mode_config.connector_list, head) { if (connector->connector_type != DRM_MODE_CONNECTOR_LVDS && connector->connector_type != DRM_MODE_CONNECTOR_eDP)