Re: [Intel-gfx] Linux 3.11-rc2 [backlight] [ASUS N56VZ]

From: * SAMÃ *
Date: Mon Jul 29 2013 - 15:36:42 EST

Hi Rafael,

did you commit a full revert?
Because I am experiencing quite weird things in rc3.
Do we have a bug opened to discuss about it?

Here is what I can observe:
1) During boot, probably when loading the driver, backlight gets off (or to a level low enough to make me feel it is off)
2) When I am playing with my Fn+x keys, I am getting a completely full / completely low brightness with no intermediate steps
3) When I am playing with my Fn+x keys while gnome brightness settings panel is open, I am recovering intermediate steps but the Fn+x keys behavior is inverted (the key supposed to lower the brightness make it increase and vice-versa. Note that the gnome brightness indicator also gets inverted).
4) Playing with the mouse on gnome brightness settings is working, except that on the minimum level, backlight gets off
5) Writing to /sys/class/backlight/intel_backlight/brightness works


On 07/25/2013 02:57 PM, Rafael J. Wysocki wrote:
On Thursday, July 25, 2013 03:34:10 PM Jani Nikula wrote:
On Thu, 25 Jul 2013, "Rafael J. Wysocki" <rjw@xxxxxxx> wrote:
On Thursday, July 25, 2013 11:09:27 AM Jani Nikula wrote:
On Thu, 25 Jul 2013, "Rafael J. Wysocki" <rjw@xxxxxxx> wrote:
Well, I wonder what about the appended (untested) patch?
Rafael, before going there, I've been trying to wrap my (poor, rusty
after vacation) head around

commit 8c5bd7adb2ce47e6aa39d17b2375f69b0c0aa255
Author: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Date: Thu Jul 18 02:08:06 2013 +0200

ACPI / video / i915: No ACPI backlight if firmware expects Windows 8

and I can't see how it could work.
Well, if it didn't work, people wouldn't see either improvement or breakage
from it, but they do see that, so it evidently works. :-)
I didn't claim it didn't work, just that *I* didn't see how it could. ;)

First, the ACPI_VIDEO_SKIP_BACKLIGHT flag seems to be checked before
it's actually set anywhere.
Are you sure about that?

acpi_video_bus_add() is the .add() callback routine for acpi_video_bus which
in fact is an ACPI driver (the naming sucks, but I didn't invent it). This
means that acpi_video_bus_add() can only be called *after* acpi_video_bus
has been registered with the ACPI subsystem (and the driver core). That
is done by acpi_bus_register_driver() and, guess what?, this happens in
__acpi_video_register(). So clearly, acpi_video_bus_add() *cannot* run before
Right. I totally missed the call within the ternary operator. Thanks for
the explanation, and apologies for the noise.

Second, with i915 that has opregion support, __acpi_video_register()
should only ever get called once. Which means the acpi_walk_namespace()
with video_unregister_backlight() should never get called in register.

Please enlighten me.
Actually, that's correct, so we don't need the whole
video_unregister_backlight() thing, calling acpi_video_backlight_quirks() would
be sufficient.

Ah, one more reason to do a full revert. I'm thinking, though, that I'll leave
acpi_video_backlight_quirks() as is so that it can be used by
acpi_video_bus_(start)|(stop)_devices(), because that doesn't seem to cause
problems to happen.
I observe that for the regular non-quirk acpi_video_register() call,
acpi_video_backlight_quirks() won't be called during register, but it
will get called later. This might have subtle effects later on, don't
you think?
Yes, it might, but after dropping ACPI_VIDEO_SKIP_BACKLIGHT it should be OK.

As to the original problem, and your patch in this thread, what do you
think about having another value in acpi_backlight kernel parameter for
it? Having an i915 module parameter to tell acpi to use or not use
quirks seems odd, since the i915 is not really taking over
anything. It's just passing the info on to acpi.
I agree, I'm going to send a full revert in a while and we'll think what to
do about all that later.


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