From: Jingoo Han <jg1.han@samsung.com>
To: "'Lars-Peter Clausen'" <lars@metafoo.de>
Cc: "'Thierry Reding'" <thierry.reding@avionic-design.de>,
        linux-kernel@vger.kernel.org, "'Sascha Hauer'" <kernel@pengutronix.de>,
        linux-arm-kernel@lists.infradead.org,
        "'Dmitry Torokhov'" <dmitry.torokhov@gmail.com>,
        linux-input@vger.kernel.org, "'Bryan Wu'" <bryan.wu@canonical.com>,
        "'Richard Purdie'" <rpurdie@rpsys.net>, linux-leds@vger.kernel.org,
        "'Florian Tobias Schandinat'" <FlorianSchandinat@gmx.de>,
        linux-fbdev@vger.kernel.org,
        "=?utf-8?Q?'Beno=C3=AEt_Th=C3=A9baudeau'?=" 
	<benoit.thebaudeau@advansee.com>,
        "'Jingoo Han'" <jg1.han@samsung.com>
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 <50364FA4.7000401@metafoo.de>
In-reply-to: <50364FA4.7000401@metafoo.de>
Subject: Re: [PATCH] pwm: Call pwm_enable() before pwm_config()
Date: Thu, 30 Aug 2012 16:10:11 +0900
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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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