[PATCH 1/1][Oneiric SRU] Platform: Brightness quirk for samsung laptop driver

[Andy Whitcroft]

On Fri, Dec 02, 2011 at 02:29:28PM -0600, Seth Forshee wrote:
> From: Jason Stubbs <jasonbstubbs at 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 at gmail.com>
> Tested-by: David Herrmann <dh.herrmann at googlemail.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh at suse.de>
> Signed-off-by: Matthew Garrett <mjg at redhat.com>
> 
> (cherry picked from commit ac080523141d5bfa5f60ef2436480f645f915e9c)
> BugLink: http://bugs.launchpad.net/bugs/897378
> Signed-off-by: Seth Forshee <seth.forshee at canonical.com>
> ---
>  drivers/platform/x86/samsung-laptop.c |   43 +++++++++++++++++++++++++++++++++
>  1 files changed, 43 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/platform/x86/samsung-laptop.c b/drivers/platform/x86/samsung-laptop.c
> index ec85987..c32dc39 100644
> --- a/drivers/platform/x86/samsung-laptop.c
> +++ b/drivers/platform/x86/samsung-laptop.c
> @@ -226,6 +226,7 @@ static struct backlight_device *backlight_device;
>  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_brightness)
>  {
>  	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);

So I take it the quirk here is to flick to 0 and back to the new
brightness.  As we can read the brightness could we just do like:

	while (user_level != read_brightness())
		sabi_set_command(sabi_config->commands.set_brightness,
							user_level);

Either way it looks fine.

-apw