[PATCH resend 1/4] nouveau: Don't check acpi_video_backlight_support() before registering backlight

[Ben Skeggs]

On Thu, May 22, 2014 at 9:30 AM, Rafael J. Wysocki <rjw at rjwysocki.net> wrote:
> On Wednesday, May 21, 2014 03:39:53 PM Hans de Goede wrote:
>> 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 at redhat.com>
>
> It would be good to have an ACK from the nouveau people for this one.
Acked-by: Ben Skeggs <bskeggs at 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)
>>
>
> --
> I speak only for myself.
> Rafael J. Wysocki, Intel Open Source Technology Center.
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