Hi, On 05/22/2014 01:30 AM, Rafael J. Wysocki 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@xxxxxxxxxx> > > It would be good to have an ACK from the nouveau people for this one. Right, it could / should even go in through the drm tree I guess. Regards, Hans -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
