linux-kernel - Re: [PATCH v3] leds: add LM3533 LED driver

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Date:	Mon, 14 May 2012 12:25:57 +0200
From:	Johan Hovold <jhovold@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Johan Hovold <jhovold@...il.com>,
	Richard Purdie <rpurdie@...ys.net>,
	Rob Landley <rob@...dley.net>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Jonathan Cameron <jic23@....ac.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Florian Tobias Schandinat <FlorianSchandinat@....de>,
	Arnd Bergmann <arnd@...db.de>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	Bryan Wu <bryan.wu@...onical.com>
Subject: Re: [PATCH v3] leds: add LM3533 LED driver

On Fri, May 11, 2012 at 03:24:36PM -0700, Andrew Morton wrote:
> On Fri, 11 May 2012 11:54:11 +0200
> Johan Hovold <jhovold@...il.com> wrote:
> > On Thu, May 10, 2012 at 11:48:17AM -0700, Andrew Morton wrote:
> > > On Thu, 10 May 2012 20:27:05 +0200
> > > Johan Hovold <jhovold@...il.com> wrote:
> > > 
> > > > Add sub-driver for the LEDs on National Semiconductor / TI LM3533
> > > > lighting power chips.
> > > > 
> > > > The chip provides 256 brightness levels, hardware accelerated blinking
> > > > as well as ambient-light-sensor and pwm input control.

[...]

> > > > +static ssize_t store_als(struct device *dev,
> > > > +					struct device_attribute *attr,
> > > > +					const char *buf, size_t len)
> > > > +{
> > > > +	struct led_classdev *led_cdev = dev_get_drvdata(dev);
> > > > +	struct lm3533_led *led = to_lm3533_led(led_cdev);
> > > > +	u8 als;
> > > > +	u8 reg;
> > > > +	u8 mask;
> > > > +	int ret;
> > > > +
> > > > +	if (kstrtou8(buf, 0, &als))
> > > > +		return -EINVAL;
> > > > +
> > > > +	if (als != 0 && (als < LM3533_ALS_LV_MIN || als > LM3533_ALS_LV_MAX))
> > > > +		return -EINVAL;
> > > 
> > > The `als != 0' test doesn't do anything, and looks odd.  Is there some
> > > magical reason why als==0 would be illegal even if LM3533_ALS_LV_MIN
> > > was negative?  If so, it should be documented.
> > 
> > The non-zero-test is not redundant as 0 is the only valid input outside
> > of [LV_MIN,LV_MAX] (in fact, the only three valid values are 0,2 and 3).
> 
> ah, OK.  One day I'll get the hang of this C thingy.
> 
> > Would you prefer
> > 
> > 	if ((als < LM3533_ALS_LV_MIN && als != 0) || als > LM3533_ALS_LV_MAX)
> > 		return -EINVAL;
> > 
> > or nested conditionals? Or should I simply add a comment?
> 
> A comment would be nice.  That 0 is also permitted is a surprise.

Actually, there is a comment already documenting the valid values and
it's placed above the show function immediately above the store one:

/*
 * ALS-control setting:
 *
 *   0 - ALS disabled
 *   2 - ALS-mapper 2
 *   3 - ALS-mapper 3
 */
static ssize_t show_als(struct device *dev,
...
static ssize_t store_als(struct device *dev,


Thanks,
Johan
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