linux-kernel - [19/48] [PATCH] ideapad: Check if acpi already handle backlight power to avoid a page fault

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Message-Id: <20120116184517.406491648@clark.kroah.org>
Date:	Mon, 16 Jan 2012 10:44:46 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Rene Bolldorf <xsecute@...glemail.com>,
	Matthew Garrett <mjg@...hat.com>,
	Jonathan Nieder <jrnieder@...il.com>
Subject: [19/48] [PATCH] ideapad: Check if acpi already handle backlight power to avoid a page fault

3.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Rene Bollford <xsecute@...glemail.com>

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@...glemail.com>
Signed-off-by: Matthew Garrett <mjg@...hat.com>
Signed-off-by: Jonathan Nieder <jrnieder@...il.com>
Tested-by: Artem X <artem.brz@...il.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/platform/x86/ideapad-laptop.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/platform/x86/ideapad-laptop.c
+++ b/drivers/platform/x86/ideapad-laptop.c
@@ -493,6 +493,8 @@ static void ideapad_backlight_notify_pow
 	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;


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