acpi_video_backlight_support() is supposed to be called by other (vendor specific) firmware backlight controls, not by native / raw backlight controls like nv_backlight.

Userspace will normally prefer firmware interfaces over raw interfaces, so if acpi_video backlight support is present it will use that even if nv_backlight is registered as well.

Except when video.use_native_backlight is present on the kernel cmdline (or enabled through a dmi based quirk). As the name indicates the goal here is to make only the raw interface available to userspace so that it will use that (it only does this when it sees a win8 compliant bios).

This is done by: 1) Not registering any acpi_video# backlight devices; and 2) Making acpi_video_backlight_support() return true so that other firmware drivers, ie acer_wmi, thinkpad_acpi, dell_laptop, etc. Don't register their own vender specific interfaces.

Currently nouveau breaks this setup, as when acpi_video_backlight_support() returns true, it does not register itself, resulting in no backlight control at all.

This is esp. going to be a problem with 3.16 which will default to video.use_native_backlight=1, and thus nouveau based laptops with a win8 bios will get no backlight control at all.

This also likely explains why the previous attempt to make video.use_native_backlight=1 the default was not a success, as without this patch having a default of video.use_native_backlight=1 will cause regressions.

Note this effectively reverts commit 5bead799

Also see: https://bugzilla.redhat.com/show_bug.cgi?id=1093171

Signed-off-by: Hans de Goede hdegoede@redhat.com --- drivers/gpu/drm/nouveau/nouveau_backlight.c | 9 --------- 1 file changed, 9 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_backlight.c b/drivers/gpu/drm/nouveau/nouveau_backlight.c index 630f6e8..2c1e4aa 100644 --- a/drivers/gpu/drm/nouveau/nouveau_backlight.c +++ b/drivers/gpu/drm/nouveau/nouveau_backlight.c @@ -31,7 +31,6 @@ */

#include <linux/backlight.h> -#include <linux/acpi.h>

#include "nouveau_drm.h" #include "nouveau_reg.h" @@ -222,14 +221,6 @@ nouveau_backlight_init(struct drm_device *dev) struct nouveau_device *device = nv_device(drm->device); struct drm_connector *connector;

-#ifdef CONFIG_ACPI - if (acpi_video_backlight_support()) { - NV_INFO(drm, "ACPI backlight interface available, " - "not registering our own\n"); - return 0; - } -#endif - 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)