From: benoit.thebaudeau@advansee.com (Benoît Thébaudeau)
To: linux-arm-kernel@lists.infradead.org
Subject: [BUG] leds-pwm: First setting of brightness does nothing
Date: Thu, 23 Aug 2012 15:36:54 +0200 (CEST) [thread overview]
Message-ID: <320569847.2756382.1345729013971.JavaMail.root@advansee.com> (raw)
In-Reply-To: <322770447.2755463.1345727876098.JavaMail.root@advansee.com>
Hi all,
I have found a bug using leds-pwm with the i.MX PWM driver. The first time a
non-0 brightness is set through sysfs, this has no effect. It works fine from
the 2nd time.
The cause of this bug is that leds-pwm.c:led_pwm_set() calls pwm_config() before
pwm_enable(), while in the i.MX PWM driver pwm_enable() enables the PWM IP
clock, so that a call to pwm_config() has no effect before the first call to
pwm_enable().
Several other PWM drivers in drivers/pwm/ work in the same way. pwm-beeper.c and
pwm_bl.c also call pwm_config() before pwm_enable(). The PWM documentation does
not say if the wrong doers are these PWM users or the i.MX-like PWM drivers.
So what should be fixed? Fixing these PWM users would be quite easy since it's a
simple swap of the pwm_config() and pwm_enable() calls. This should not produce
any glitch since the duty cycle is always set to 0 by these PWM users before
calling pwm_disable().
Best regards,
Beno?t
WARNING: multiple messages have this Message-ID (diff)
From: "Benoît Thébaudeau" <benoit.thebaudeau@advansee.com>
To: Bryan Wu <bryan.wu@canonical.com>,
Richard Purdie <rpurdie@rpsys.net>,
linux-leds@vger.kernel.org,
Thierry Reding <thierry.reding@avionic-design.de>,
linux-kernel@vger.kernel.org,
Sascha Hauer <s.hauer@pengutronix.de>,
linux-arm-kernel@lists.infradead.org
Cc: "Benoît Thébaudeau" <benoit.thebaudeau@advansee.com>
Subject: [BUG] leds-pwm: First setting of brightness does nothing
Date: Thu, 23 Aug 2012 15:36:54 +0200 (CEST) [thread overview]
Message-ID: <320569847.2756382.1345729013971.JavaMail.root@advansee.com> (raw)
In-Reply-To: <322770447.2755463.1345727876098.JavaMail.root@advansee.com>
Hi all,
I have found a bug using leds-pwm with the i.MX PWM driver. The first time a
non-0 brightness is set through sysfs, this has no effect. It works fine from
the 2nd time.
The cause of this bug is that leds-pwm.c:led_pwm_set() calls pwm_config() before
pwm_enable(), while in the i.MX PWM driver pwm_enable() enables the PWM IP
clock, so that a call to pwm_config() has no effect before the first call to
pwm_enable().
Several other PWM drivers in drivers/pwm/ work in the same way. pwm-beeper.c and
pwm_bl.c also call pwm_config() before pwm_enable(). The PWM documentation does
not say if the wrong doers are these PWM users or the i.MX-like PWM drivers.
So what should be fixed? Fixing these PWM users would be quite easy since it's a
simple swap of the pwm_config() and pwm_enable() calls. This should not produce
any glitch since the duty cycle is always set to 0 by these PWM users before
calling pwm_disable().
Best regards,
Benoît
next parent reply other threads:[~2012-08-23 13:36 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <322770447.2755463.1345727876098.JavaMail.root@advansee.com>
2012-08-23 13:36 ` Benoît Thébaudeau [this message]
2012-08-23 13:36 ` [BUG] leds-pwm: First setting of brightness does nothing Benoît Thébaudeau
2012-08-23 14:19 ` [PATCH] pwm: Call pwm_enable() before pwm_config() Benoît Thébaudeau
2012-08-23 14:19 ` Benoît Thébaudeau
2012-08-23 14:19 ` Benoît Thébaudeau
2012-08-23 14:19 ` Benoît Thébaudeau
2012-08-23 15:43 ` Lars-Peter Clausen
2012-08-23 15:43 ` Lars-Peter Clausen
2012-08-23 15:43 ` Lars-Peter Clausen
2012-08-30 7:10 ` Jingoo Han
2012-08-30 7:10 ` Jingoo Han
2012-08-30 7:10 ` Jingoo Han
2012-08-23 16:57 ` Benoît Thébaudeau
2012-08-23 16:57 ` Benoît Thébaudeau
2012-08-23 16:57 ` Benoît Thébaudeau
2012-08-23 16:57 ` Benoît Thébaudeau
2012-08-23 17:12 ` Lars-Peter Clausen
2012-08-23 17:12 ` Lars-Peter Clausen
2012-08-23 17:12 ` Lars-Peter Clausen
2012-08-23 17:19 ` Lars-Peter Clausen
2012-08-23 17:19 ` Lars-Peter Clausen
2012-08-23 17:19 ` Lars-Peter Clausen
2012-08-23 19:04 ` Thierry Reding
2012-08-23 19:04 ` Thierry Reding
2012-08-23 19:04 ` Thierry Reding
2012-09-20 19:05 ` Mark Brown
2012-09-20 19:05 ` Mark Brown
2012-09-20 19:05 ` Mark Brown
2012-08-23 19:11 ` Thierry Reding
2012-08-23 19:11 ` Thierry Reding
2012-08-23 19:11 ` Thierry Reding
2012-08-23 20:58 ` [PATCH] pwm-imx: Fix config / enable / disable Benoît Thébaudeau
2012-08-23 21:03 ` Benoît Thébaudeau
2012-08-23 21:03 ` Benoît Thébaudeau
2012-08-23 21:03 ` Benoît Thébaudeau
2012-08-28 7:37 ` Sascha Hauer
2012-08-28 7:37 ` Sascha Hauer
2012-08-28 7:37 ` Sascha Hauer
2012-08-28 7:37 ` Sascha Hauer
2012-09-20 19:03 ` [PATCH] pwm: Call pwm_enable() before pwm_config() Mark Brown
2012-09-20 19:03 ` Mark Brown
2012-09-20 19:03 ` Mark Brown
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