linux-kernel - RE: [PATCH] s3c/s3c24xx: arm: leds: Make s3c24xx LEDS driver use gpiolib

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Message-ID: <74CDBE0F657A3D45AFBB94109FB122FF1740D74FAD@HQMAIL01.nvidia.com>
Date:	Fri, 18 Nov 2011 13:59:33 -0800
From:	Stephen Warren <swarren@...dia.com>
To:	Denis Kuzmenko <linux@...onet.org.ua>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Linus Walleij <linus.walleij@...aro.org>,
	Richard Purdie <rpurdie@...ys.net>,
	Wolfram Sang <w.sang@...gutronix.de>
Subject: RE: [PATCH] s3c/s3c24xx: arm: leds: Make s3c24xx LEDS driver use
 gpiolib

Denis Kuzmenko wrote at Friday, November 18, 2011 2:45 PM:
> Make s3c24xx LEDS driver use gpiolib. Disable using pull-resistor when not
> using S3C24XX_LEDF_TRISTATE and enble it when in opposite case.
> 
> Signed-off-by: Denis Kuzmenko <linux@...onet.org.ua>

>  	if (pdata->flags & S3C24XX_LEDF_TRISTATE) {
> -		s3c2410_gpio_setpin(pdata->gpio, 0);
> -		s3c2410_gpio_cfgpin(pdata->gpio, S3C2410_GPIO_INPUT);
> +		/*
> +		 * pull is needed here to protect pin from being left
> +		 * floating
> +		 */
> +		ret = s3c_gpio_setpull(pdata->gpio, S3C_GPIO_PULL_UP);
> +		if (ret)
> +			s3c_gpio_setpull(pdata->gpio, S3C_GPIO_PULL_DOWN);

Sorry, could you explain why it's appropriate to configure a pull here
at all, let alone why it's OK to have a random pull on the line?

> +		/* initially turn off led */
> +		ret = gpio_direction_input(pdata->gpio);
>  	} else {
> -		s3c2410_gpio_pullup(pdata->gpio, 0);
> -		s3c2410_gpio_setpin(pdata->gpio, 0);
> -		s3c2410_gpio_cfgpin(pdata->gpio, S3C2410_GPIO_OUTPUT);
> +		/* no point in having a pull-up as we are always driving */
> +		s3c_gpio_setpull(pdata->gpio, S3C_GPIO_PULL_NONE);
> +		ret = gpio_request_one(pdata->gpio, GPIOF_OUT_INIT_LOW,
> +								pdata->name);
> +		/* initially turn off led */
> +		ret = gpio_direction_output(pdata->gpio,
> +				!!(pdata->flags & S3C24XX_LEDF_ACTLOW));

Wouldn't it be better to pass GPIOF_OUT_INIT_HIGH or GPIOF_OUT_INIT_LOW
to gpio_request_one() based on S3C24XX_LEDF_ACTLOW, and avoid the call to
gpio_direction_output; that will avoid glitching the line for a short time.

I'm fine with the rest of the code.

-- 
nvpublic

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