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

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Message-Id: <201208200537.48993.arnd@arndb.de>
Date:	Mon, 20 Aug 2012 05:37:48 +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:
> +#ifdef CONFIG_PWM
> +static int lm3530_pwm_request(struct lm3530_data *drvdata)
> +{
> +       int pwm_id;
> +
> +       /* if the pwm device exists, skip requesting the device */
> +       if (drvdata->pwm)
> +               return 0;
> +
> +       pwm_id = drvdata->pdata ? drvdata->pdata->pwm_id : 0;
> +
> +       drvdata->pwm = pwm_request(pwm_id, "lm3530-pwm");
> +       drvdata->period_ns = drvdata->pdata ? drvdata->pdata->period_ns : 0;
> +
> +       return IS_ERR(drvdata->pwm) ? PTR_ERR(drvdata->pwm) : 0;
> +}
> +

A few comments on this:

* Rather than having to do the #ifdef here, I think it would be better if
  the PWM subsystem provided stub functions for pwm_request, pwm_config,
  pwm_enable, pwm_disable and pwm_free that do nothing, so you can in effect
  let the compiler optimize away the above code.

* 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.

	Arnd
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