Re: [PATCH linux-3.1.y] ideapad: Check if acpi already handle backlight power to avoid a page fault

[Ike Panhc <ike.pan@canonical.com>]

Thanks, and this is necessary for 3.1.y

On 01/11/2012 08:42 AM, Jonathan Nieder wrote:
> From: René Bollford <xsecute@googlemail.com>
> Date: Sun, 23 Oct 2011 09:56:42 +0200
> 
> commit d4afc7754a60b885b63ef23fd194984e2d53a4e6 upstream.
> 
> This patch avoid a page fault in the ideapad-laptop extras when
> turning the backlight power on or off.
> 
> Signed-off-by: Rene Bolldorf <xsecute@googlemail.com>
> Signed-off-by: Matthew Garrett <mjg@redhat.com>
> Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
> Tested-by: Artem X <artem.brz@gmail.com>

Acked-by: Ike Panhc <ike.pan@canonical.com>

> ---
> Artem X wrote:
> 
>> I've compiled vanilla 3.1.6 with that patch and turning off blacklight
>> was working.
> 
> This fixes an oops reported by a few people in the new ideapad-laptop
> backlight driver.  See:
> 
>  - http://thread.gmane.org/gmane.linux.kernel/1205259
>  - http://thread.gmane.org/gmane.linux.drivers.platform.x86.devel/2405
>  - http://bugs.debian.org/655377
> 
> Luckily the ideapad-laptop backlight driver was introduced in
> v3.1-rc1~14^2~29, so older kernels do not have this bug.  Fix is
> already included in v3.2.
> 
>  drivers/platform/x86/ideapad-laptop.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/platform/x86/ideapad-laptop.c b/drivers/platform/x86/ideapad-laptop.c
> index 0c595410e788..0d94eec00f4d 100644
> --- a/drivers/platform/x86/ideapad-laptop.c
> +++ b/drivers/platform/x86/ideapad-laptop.c
> @@ -493,6 +493,8 @@ static void ideapad_backlight_notify_power(struct ideapad_private *priv)
>  	unsigned long power;
>  	struct backlight_device *blightdev = priv->blightdev;
>  
> +	if (!blightdev)
> +		return;
>  	if (read_ec_data(ideapad_handle, 0x18, &power))
>  		return;
>  	blightdev->props.power = power ? FB_BLANK_UNBLANK : FB_BLANK_POWERDOWN;