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pwm_bl: Fix overflow condition

PATCH In review Derek Basehore 1 participant 2 messages Aug 29, 2017

Subsystems (3)
Framebuffer layer PWM Backlight class/subsystem
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Derek Basehore

author
#0 lore raw

PATCH v2 1/1 pwm_bl: Fix overflow condition

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.

Change-Id I745c67c7a24740316d13eaf1be74248ea2249353
Signed-off-by Derek Basehore <[email protected]>
---
 drivers/video/backlight/pwm_bl.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)
drivers/video/backlight/pwm_bl.c +5 -2
index 76311ec5e400..5ccc8e34b7a6 100644
@@ -88,14 +88,17 @@ 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)
Signature · 1 line
2.14.1.342.g6490525c54-goog
author
#1 lore raw

Okay, I think that this is just my email client confusing me. Please ignore this email and just review the first "PATCH v2" patch.