This is a note to let you know that I've just added the patch titled
ACPI / video: Quirk initial backlight level 0
to the 3.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
acpi-video-quirk-initial-backlight-level-0.patch
and it can be found in the queue-3.12 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 2c62333a408f5badd2d2ffd7177f95deeccc5ca4 Mon Sep 17 00:00:00 2001
From: Aaron Lu <aaron.lu@xxxxxxxxx>
Date: Wed, 6 Nov 2013 09:07:10 +0800
Subject: ACPI / video: Quirk initial backlight level 0
From: Aaron Lu <aaron.lu@xxxxxxxxx>
commit 2c62333a408f5badd2d2ffd7177f95deeccc5ca4 upstream.
Some firmware doesn't initialize initial backlight level to a proper
value and _BQC will return 0 on first time evaluation. We used to be
able to detect such incorrect value with our code logic, as value 0
normally isn't a valid value in _BCL. But with the introduction of Win8,
firmware begins to fill _BCL with values from 0 to 100, now 0 becomes
a valid value but that value will make user's screen black. This patch
test initial _BQC for value 0, if such a value is returned, do not use
it.
References: https://bugzilla.kernel.org/show_bug.cgi?id=64031
References: https://bugzilla.kernel.org/show_bug.cgi?id=61231
References: https://bugzilla.kernel.org/show_bug.cgi?id=63111
Reported-by: Qingshuai Tian <qingshuai.tian@xxxxxxxxx>
Tested-by: Aaron Lu <aaron.lu@xxxxxxxxx> # on "Idealpad u330p"
Reported-and-tested-by: <erno@xxxxxx> # on "Acer Aspire V5-573G"
Reported-and-tested-by: Kirill Tkhai <tkhai@xxxxxxxxx> # on "HP 250 G1"
Signed-off-by: Aaron Lu <aaron.lu@xxxxxxxxx>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/acpi/video.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/drivers/acpi/video.c
+++ b/drivers/acpi/video.c
@@ -832,7 +832,7 @@ acpi_video_init_brightness(struct acpi_v
for (i = 2; i < br->count; i++)
if (level_old == br->levels[i])
break;
- if (i == br->count)
+ if (i == br->count || !level)
level = max_level;
}
Patches currently in stable-queue which might be from aaron.lu@xxxxxxxxx are
queue-3.12/acpi-video-quirk-initial-backlight-level-0.patch
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