From: Derek Basehore <dbasehore@chromium.org>
Date: Tue, 29 Aug 2017 20:34:34 +0000 (-0700)
Subject: backlight: pwm_bl: Fix overflow condition
X-Git-Tag: v4.14.9~75
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=b04c22da18b53c7be730478282f7e6f62cef9425;p=platform%2Fkernel%2Flinux-rpi.git

backlight: pwm_bl: Fix overflow condition


[ 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>
---

diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index 9bd1768..1c2289d 100644
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -79,14 +79,17 @@ static void pwm_backlight_power_off(struct pwm_bl_data *pb)
 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)