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

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Date:	Mon, 20 Aug 2012 06:13:20 +0000
From:	"Kim, Milo" <Milo.Kim@...com>
To:	Arnd Bergmann <arnd@...db.de>
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

> * 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.

Thanks a lot for catching this!

This is really what I'm hesitating to use #ifdef.
Do you mean making PWM exported functions in pwm.h with CONFIG_PWM condition as below?

#ifdef CONFIG_PWM
...
int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns);
...
#else
...
static inline int pwm_config(struct pwm_device *pwm, int duty_ns, int period_ns)
{
	return 0;
}
...
#endif


> * 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.


Best Regards,
Milo



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