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Subject[patch 6/8] Platform: Brightness quirk for samsung laptop driver
From: Jason Stubbs <jasonbstubbs@gmail.com>

On some Samsung laptops the brightness regulation works slightly different.
All SABI commands except for set_brightness work as expected. The behaviour
of set_brightness is as follows:

- Setting a new brightness will only step one level toward the new brightness
level. For example, setting a level of 5 when the current level is 2 will
result in a brightness level of 3.
- A spurious KEY_BRIGHTNESS_UP or KEY_BRIGHTNESS_DOWN event is also generated
along with the change in brightness.
- Neither of the above two issues occur when changing from/to brightness
level 0.

This patch adds detection and a non-intrusive workaround for the above issues.

Signed-off-by: Jason Stubbs <jasonbstubbs@gmail.com>
Tested-by: David Herrmann <dh.herrmann@googlemail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
drivers/platform/x86/samsung-laptop.c | 43 ++++++++++++++++++++++++++++++++++
1 file changed, 43 insertions(+)
--- a/drivers/platform/x86/samsung-laptop.c
+++ b/drivers/platform/x86/samsung-laptop.c
@@ -226,6 +226,7 @@ static struct backlight_device *backligh
static struct mutex sabi_mutex;
static struct platform_device *sdev;
static struct rfkill *rfk;
+static bool has_stepping_quirk;

static int force;
module_param(force, bool, 0);
@@ -382,6 +383,17 @@ static void set_brightness(u8 user_brigh
{
u8 user_level = user_brightness + sabi_config->min_brightness;

+ if (has_stepping_quirk && user_level != 0) {
+ /*
+ * short circuit if the specified level is what's already set
+ * to prevent the screen from flickering needlessly
+ */
+ if (user_brightness == read_brightness())
+ return;
+
+ sabi_set_command(sabi_config->commands.set_brightness, 0);
+ }
+
sabi_set_command(sabi_config->commands.set_brightness, user_level);
}

@@ -390,6 +402,34 @@ static int get_brightness(struct backlig
return (int)read_brightness();
}

+static void check_for_stepping_quirk(void)
+{
+ u8 initial_level = read_brightness();
+ u8 check_level;
+
+ /*
+ * Some laptops exhibit the strange behaviour of stepping toward
+ * (rather than setting) the brightness except when changing to/from
+ * brightness level 0. This behaviour is checked for here and worked
+ * around in set_brightness.
+ */
+
+ if (initial_level <= 2)
+ check_level = initial_level + 2;
+ else
+ check_level = initial_level - 2;
+
+ has_stepping_quirk = false;
+ set_brightness(check_level);
+
+ if (read_brightness() != check_level) {
+ has_stepping_quirk = true;
+ pr_info("enabled workaround for brightness stepping quirk\n");
+ }
+
+ set_brightness(initial_level);
+}
+
static int update_status(struct backlight_device *bd)
{
set_brightness(bd->props.brightness);
@@ -823,6 +863,9 @@ static int __init samsung_init(void)
}
}

+ /* Check for stepping quirk */
+ check_for_stepping_quirk();
+
/* knock up a platform device to hang stuff off of */
sdev = platform_device_register_simple("samsung", -1, NULL, 0);
if (IS_ERR(sdev))



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