linux-kernel - [PATCH] RFC: leds-pwm: don't disable pwm when setting brightness to 0

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Date:	Wed, 24 Oct 2012 15:52:46 +0200
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Thierry Reding <thierry.reding@...onic-design.de>,
	Shawn Guo <shawn.guo@...aro.org>, kernel@...gutronix.de
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Bryan Wu <bryan.wu@...onical.com>,
	Richard Purdie <rpurdie@...ys.net>, linux-leds@...r.kernel.org
Subject: [PATCH] RFC: leds-pwm: don't disable pwm when setting brightness to 0

This fixes disabling the LED on i.MX28. The PWM hardware delays using
the newly set pwm-config until the beginning of a new period.  It's very
likely that pwm_disable is called before the current period ends. In
case the LED was on brightness=max before the LED stays on because in
the disabled PWM block the period never ends.

It's unclear if the mxs-pwm driver doesn't implement the API as expected
(i.e. it should block until the newly set config is effective) or if the
leds-pwm driver makes wrong assumptions. This patch assumes the latter.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
---
Hello,

I'm not sure this is correct, but this is the workaround I'm using until
I get some feed back.

Best regards
Uwe

 drivers/leds/leds-pwm.c |    9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/drivers/leds/leds-pwm.c b/drivers/leds/leds-pwm.c
index f2e44c7..a909f4f 100644
--- a/drivers/leds/leds-pwm.c
+++ b/drivers/leds/leds-pwm.c
@@ -38,13 +38,8 @@ static void led_pwm_set(struct led_classdev *led_cdev,
 	unsigned int max = led_dat->cdev.max_brightness;
 	unsigned int period =  led_dat->period;
 
-	if (brightness == 0) {
-		pwm_config(led_dat->pwm, 0, period);
-		pwm_disable(led_dat->pwm);
-	} else {
-		pwm_config(led_dat->pwm, brightness * period / max, period);
-		pwm_enable(led_dat->pwm);
-	}
+	pwm_config(led_dat->pwm, brightness * period / max, period);
+	pwm_enable(led_dat->pwm);
 }
 
 static int led_pwm_probe(struct platform_device *pdev)
-- 
1.7.10.4

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