Platform: Detect samsung laptop quirk when initial level is zero
 

BugLink: http://bugs.launchpad.net/bugs/810093

== SRU Justification ==

Impact: Many Samsung notebook models require a quirk for adjusting the
screen brightness, but in some cases the quirk detection fails and the
wrong backlight adjustment method is used.

Fix: Upstream cherry pick to fix quirk detection.

Test Case: Verified on LP #810093 on the Samsung N220P.

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Platform: Detect samsung laptop quirk when initial level is zero
 

From: John Serock <john.serock@gmail.com>

This patch depends on the "Platform: Brightness quirk for samsung
laptop driver" patch from Jason Stubbs. This patch adds a check for an
initial brightness level of 0; if the level is 0, this patch changes
the brightness level to 1 before the driver attempts to detect the
brightness quirk.

The Samsung N150 netbook experiences the brightness quirk. Without
Jason's patch, the only brightness levels available on the N150 are 0,
1, and 8. This patch ensures that, when the initial brightness level
is 0, the samsang-laptop driver detects the brightness quirk on the
N150, thereby making brightness levels 0 through 8 available.

Signed-off-by: John Serock <john.serock@gmail.com>
Acked-by: Jason Stubbs <jasonbstubbs@gmail.com>
Signed-off-by: Matthew Garrett <mjg@redhat.com>

(cherry picked from commit ba05b237372bad82533d1f717569d1d817ff3c27)
BugLink: http://bugs.launchpad.net/bugs/810093
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
---
drivers/platform/x86/samsung-laptop.c | 10 ++++++++--
1 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/platform/x86/samsung-laptop.c b/drivers/platform/x86/samsung-laptop.c
index c32dc39..e553486 100644
--- a/drivers/platform/x86/samsung-laptop.c
+++ b/drivers/platform/x86/samsung-laptop.c
@@ -404,8 +404,9 @@ static int get_brightness(struct backlight_device *bd)

static void check_for_stepping_quirk(void)
{
- u8 initial_level = read_brightness();
+ u8 initial_level;
u8 check_level;
+ u8 orig_level = read_brightness();

/*
* Some laptops exhibit the strange behaviour of stepping toward
@@ -414,6 +415,11 @@ static void check_for_stepping_quirk(void)
* around in set_brightness.
*/

+ if (orig_level == 0)
+ set_brightness(1);
+
+ initial_level = read_brightness();
+
if (initial_level <= 2)
check_level = initial_level + 2;
else
@@ -427,7 +433,7 @@ static void check_for_stepping_quirk(void)
pr_info("enabled workaround for brightness stepping quirk
");
}

- set_brightness(initial_level);
+ set_brightness(orig_level);
}

static int update_status(struct backlight_device *bd)
--
1.7.5.4


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