Patch "backlight: pwm_bl: Fix overflow condition" has been added to the 4.14-stable tree

Patch "backlight: pwm_bl: Fix overflow condition" has been added to the 4.14-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    backlight: pwm_bl: Fix overflow condition

to the 4.14-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     backlight-pwm_bl-fix-overflow-condition.patch
and it can be found in the queue-4.14 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Wed Dec 20 18:17:52 CET 2017
From: Derek Basehore <dbasehore@chromium.org>
Date: Tue, 29 Aug 2017 13:34:34 -0700
Subject: backlight: pwm_bl: Fix overflow condition

From: Derek Basehore <dbasehore@chromium.org>


[ Upstream commit 5d0c49acebc9488e37db95f1d4a55644e545ffe7 ]

This fixes an overflow condition that can happen with high max
brightness and period values in compute_duty_cycle. This fixes it by
using a 64 bit variable for computing the duty cycle.

Signed-off-by: Derek Basehore <dbasehore@chromium.org>
Acked-by: Thierry Reding <thierry.reding@gmail.com>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/video/backlight/pwm_bl.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -79,14 +79,17 @@ static void pwm_backlight_power_off(stru
 static int compute_duty_cycle(struct pwm_bl_data *pb, int brightness)
 {
 	unsigned int lth = pb->lth_brightness;
-	int duty_cycle;
+	u64 duty_cycle;
 
 	if (pb->levels)
 		duty_cycle = pb->levels[brightness];
 	else
 		duty_cycle = brightness;
 
-	return (duty_cycle * (pb->period - lth) / pb->scale) + lth;
+	duty_cycle *= pb->period - lth;
+	do_div(duty_cycle, pb->scale);
+
+	return duty_cycle + lth;
 }
 
 static int pwm_backlight_update_status(struct backlight_device *bl)


Patches currently in stable-queue which might be from dbasehore@chromium.org are

queue-4.14/backlight-pwm_bl-fix-overflow-condition.patch