linux-kernel - Re: linux-next 20160512 - ACPI issue with screen brightness

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Message-ID: <2897.1463727728@turing-police.cc.vt.edu>
Date:	Fri, 20 May 2016 03:02:08 -0400
From:	Valdis.Kletnieks@...edu
To:	Aaron Lu <aaron.lu@...el.com>
Cc:	"Rafael J. Wysocki" <rafael@...nel.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Len Brown <lenb@...nel.org>
Subject: Re: linux-next 20160512 - ACPI issue with screen brightness

On Fri, 20 May 2016 13:45:30 +0800, Aaron Lu said:
> On 05/20/2016 11:05 AM, Valdis.Kletnieks@...edu wrote:
> > On Thu, 19 May 2016 18:53:17 -0400, Valdis.Kletnieks@...edu said:
> >
> >>>> next-20160512 sets the screen brightness to about 40%-ish or so, rather
> >>>> than the 100% intensity I want.
>
> Do you mean after boot, the screen brightness is now 40% instead of the
> previous 100%? Are you using a GUI?

Nope, even the very first line of output from initramfs is dim, and if I then
reboot and go into the BIOS settings, the screen intensity is at 40%. While
it's rebooting, the Dell bios splash will start off bright and then suddenly
dim down.

With the patches reverted:

[/sys/class/backlight/acpi_video0] grep . *bright*
actual_brightness:95
brightness:95
max_brightness:95

And the weird part inside the kernel - on a kernel that has the problem,
/sys/class/backlight is *empty* - only '.' and '..' entries.

No, I don't understand why the acpi_video0 entry isn't created when that
commit is in place.

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