linux-kernel - [PATCH] backlight: pwm_bl: disable PWM when 'duty

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Date:	Mon,  6 Jun 2016 12:44:56 +0200
From:	Lothar Waßmann <LW@...O-electronics.de>
To:	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Jingoo Han <jingoohan1@...il.com>,
	Lee Jones <lee.jones@...aro.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-pwm@...r.kernel.org
Cc:	Lothar Waßmann <LW@...O-electronics.de>
Subject: [PATCH] backlight: pwm_bl: disable PWM when 'duty_cycle' is zero

'brightness' is usually an index into a table of duty_cycle values,
where the value at index 0 may well be non-zero
(tegra30-apalis-eval.dts and tegra30-colibri-eval-v3.dts are real-life
examples).
Thus brightness == 0 does not necessarily mean that the PWM output
will be inactive.
Check for 'duty_cycle == 0' rather than 'brightness == 0' to decide
whether to disable the PWM.

Signed-off-by: Lothar Waßmann <LW@...O-electronics.de>
---
 drivers/video/backlight/pwm_bl.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index b2b366b..80b2b52 100644
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -103,8 +103,8 @@ static int pwm_backlight_update_status(struct backlight_device *bl)
 	if (pb->notify)
 		brightness = pb->notify(pb->dev, brightness);
 
-	if (brightness > 0) {
-		duty_cycle = compute_duty_cycle(pb, brightness);
+	duty_cycle = compute_duty_cycle(pb, brightness);
+	if (duty_cycle > 0) {
 		pwm_config(pb->pwm, duty_cycle, pb->period);
 		pwm_backlight_power_on(pb, brightness);
 	} else
-- 
2.1.4