linux-kernel - Re: [PATCH] pwm: Call pwm_enable() before pwm

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Message-id: <002001cd867e$7e964130$7bc2c390$%han@samsung.com>
Date:	Thu, 30 Aug 2012 16:10:11 +0900
From:	Jingoo Han <jg1.han@...sung.com>
To:	'Lars-Peter Clausen' <lars@...afoo.de>
Cc:	'Thierry Reding' <thierry.reding@...onic-design.de>,
	linux-kernel@...r.kernel.org,
	'Sascha Hauer' <kernel@...gutronix.de>,
	linux-arm-kernel@...ts.infradead.org,
	'Dmitry Torokhov' <dmitry.torokhov@...il.com>,
	linux-input@...r.kernel.org, 'Bryan Wu' <bryan.wu@...onical.com>,
	'Richard Purdie' <rpurdie@...ys.net>,
	linux-leds@...r.kernel.org,
	'Florian Tobias Schandinat' <FlorianSchandinat@....de>,
	linux-fbdev@...r.kernel.org,
	'Benoît Thébaudeau' 
	<benoit.thebaudeau@...ansee.com>,
	'Jingoo Han' <jg1.han@...sung.com>
Subject: Re: [PATCH] pwm: Call pwm_enable() before pwm_config()

On Friday, August 24, 2012 12:44 AM, Lars-Peter Clausen wrote:
> 
> On 08/23/2012 04:19 PM, Benoît Thébaudeau wrote:
> > Some PWM drivers enable the clock of the PWM peripheral in pwm_enable(). Hence,
> > for these drivers, a call to pwm_config() does not have any effect before
> > pwm_enable() has been called.
> >
> > This patch fixes the PWM users to make sure that they call pwm_enable() before
> > pwm_config().
> >
> > This fixes the first setting of brightness through sysfs that had no effect with
> > leds-pwm and the i.MX PWM driver.
> 
> But isn't this a bug in the PWM peripheral driver? With this change the PWM
> will start with the old settings first. While this is not so much of a problem
> for a backlight (although it might cause a short flickering) it might cause
> problems for other applications, like using the PWM pin as a timing generator.
> In my opinion it's better to fix the PWM peripheral drivers which have this
> problem instead of trying to work around it in every user of the PWM API.

Hi Lars-Peter Clausen,

I think so.
It would be better to fix the PWM peripheral drivers.


Best regards,
Jingoo Han

> 
> - Lars
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