linux-kernel - Re: [PATCH 1/2] lp855x_bl: use generic PWM functions

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Date:	Mon, 22 Oct 2012 15:30:12 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Kim, Milo" <Milo.Kim@...com>
Cc:	Thierry Reding <thierry.reding@...onic-design.de>,
	Richard Purdie <rpurdie@...ys.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] lp855x_bl: use generic PWM functions

On Fri, 19 Oct 2012 08:45:14 +0000
"Kim, Milo" <Milo.Kim@...com> wrote:

> > Generally this looks good. Obviously you'll need to update any users of
> > this driver as well. It might make sense to include those changes in
> > this patch to avoid interim build failures.
> 
> Thanks for your review.
> So far no usages for this driver in the mainline.
> I've tested it in my own development environment instead.
> 
> > Other than that I have just one smaller comment below.
> > 
> > > +	pwm_config(lp->pwm, duty, period);
> > > +	duty == 0 ? pwm_disable(lp->pwm) : pwm_enable(lp->pwm);
> > 
> > This is really ugly and should be written explicitly:
> > 
> > 	if (duty == 0)
> > 		pwm_disable(lp->pwm);
> > 	else
> > 		pwm_enable(lp->pwm);
> 
> Oh, I prefer using '?' to if-sentence because it looks clear to me.
> But if it's difficult to read/understand, I'll fix it.
> I'd like to have others' opinion.
> 

Hey, it's better than

	(*(duty ? pwm_enable : pwm_disable))(lp->pwm);

!


But yes, the original code is unusual and I think most kernel people
would have to stare at it for a bit longer than necessary to see
exactly what it's doing.

--- a/drivers/video/backlight/lp855x_bl.c~drivers-video-backlight-lp855x_blc-use-generic-pwm-functions-fix
+++ a/drivers/video/backlight/lp855x_bl.c
@@ -139,7 +139,10 @@ static void lp855x_pwm_ctrl(struct lp855
 	}
 
 	pwm_config(lp->pwm, duty, period);
-	duty == 0 ? pwm_disable(lp->pwm) : pwm_enable(lp->pwm);
+	if (duty)
+		pwm_enable(lp->pwm);
+	else
+		pwm_disable(lp->pwm);
 }
 
 static int lp855x_bl_update_status(struct backlight_device *bl)

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