linux-kernel - Re: [PATCH 7/7] leds-lm3530: enhanced arithmetic operation

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Message-ID: <4F19267C.7010307@metafoo.de>
Date:	Fri, 20 Jan 2012 09:31:56 +0100
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	"Kim, Milo" <Milo.Kim@...com>
CC:	Linus Walleij <linus.walleij@...aro.org>,
	"shreshthakumar.sahu@...ricsson.com" 
	<shreshthakumar.sahu@...ricsson.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"rpurdie@...ys.net" <rpurdie@...ys.net>
Subject: Re: [PATCH 7/7] leds-lm3530: enhanced arithmetic operation

On 01/20/2012 02:52 AM, Kim, Milo wrote:
> Use shift operation rather than 'divide-by-2'.

The compiler will already take of this for you.

But why is the divide by two necessary anyway? This sort of looks like
max_brightness is not set properly and the code compensates for it by
ignoring the lsb.

> 
> Signed-off-by: Milo(Woogyom) Kim <milo.kim@...com>
> 
> diff --git a/drivers/leds/leds-lm3530.c b/drivers/leds/leds-lm3530.c
> index 51c1f6c..e0b1ba8 100644
> --- a/drivers/leds/leds-lm3530.c
> +++ b/drivers/leds/leds-lm3530.c
> @@ -249,12 +249,12 @@ static void lm3530_brightness_set(struct led_classdev *led_cdev,
>  
>  		/* set the brightness in brightness control register*/
>  		err = i2c_smbus_write_byte_data(drvdata->client,
> -				LM3530_BRT_CTRL_REG, brt_val / 2);
> +				LM3530_BRT_CTRL_REG, brt_val >> 1);
>  		if (err)
>  			dev_err(&drvdata->client->dev,
>  				"Unable to set brightness: %d\n", err);
>  		else
> -			drvdata->brightness = brt_val / 2;
> +			drvdata->brightness = brt_val >> 1;
>  
>  		if (brt_val == 0 && !pdata->is_vin_always_on) {
>  			err = regulator_disable(drvdata->regulator);

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