linux-kernel - Re: [PATCH] leds-lm3530: replace pwm platform functions with generic pwm functions

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Date:	Mon, 20 Aug 2012 06:45:37 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	"Kim, Milo" <Milo.Kim@...com>
Cc:	Bryan Wu <bryan.wu@...onical.com>,
	"thierry.reding@...onic-design.de" <thierry.reding@...onic-design.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] leds-lm3530: replace pwm platform functions with generic pwm functions

On Monday 20 August 2012, Kim, Milo wrote:
> > * I don't understand why you need the "if (rvdata->pwm) return 0;" case.
> >   It's normally better to do the initialization exactly once from the
> >   probe() function. You might want to return -EPROBE_DEFER if the pwm
> >   source is not yet available though.
> 
> This device has 3 control mode. - register access, sensor input and PWM input.
> One of modes can be selected on-the-fly.
> So that's why I add code which returning 0 when PWM device exists.
> Whenever mode change occurs from/to 'PWM input', pwm_request() and pwm_free() should be called.

In that case, I would recommend changing it from

+       /* if the pwm device exists, skip requesting the device */
+       if (drvdata->pwm)
+               return 0;

to 

	/* warn if the PWM was not released prior to reneabling it */
	WARN_ON(drvdata->pwm);


	Arnd
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