linux-kernel - Re: [PATCH] gpio: tegra: Implement gpio_get

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Date:	Fri, 29 Apr 2016 10:17:23 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Laxman Dewangan <ldewangan@...dia.com>
Cc:	linus.walleij@...aro.org, thierry.reding@...il.com,
	linux-gpio@...r.kernel.org, linux-tegra@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] gpio: tegra: Implement gpio_get_direction callback

On 04/29/2016 06:31 AM, Laxman Dewangan wrote:
> Implement gpio_get_direction() callback for Tegra GPIO.
> The direction is only valid if the pin is configured as
> GPIO. If pin is not configured in GPIO mode then this
> function return error.
>
> This makes debugfs and initial reading of the state of
> the lines more accurate.

> +static int tegra_gpio_get_direction(struct gpio_chip *chip, unsigned offset)
> +{
> +	struct tegra_gpio_info *tgi = gpiochip_get_data(chip);
> +	u32 pin_mask = BIT(GPIO_BIT(offset));
> +	u32 cnf, oe;
> +
> +	cnf = tegra_gpio_readl(tgi, GPIO_CNF(tgi, offset));
> +	oe = tegra_gpio_readl(tgi, GPIO_OE(tgi, offset));
> +	if (cnf & pin_mask) {
> +		if (oe & pin_mask)
> +			return GPIOF_DIR_OUT;
> +
> +		return GPIOF_DIR_IN;
> +	}
> +
> +	return -EINVAL;
> +}

Conceptually looks fine, but I have similar comments to Jon; whenever 
there's an error condition, just fail immediately. That way you avoid 
the entire rest of the function being indented:

cnf = ...
if (!(cnf ...)
     return -EINVAL;
oe = ...
return ...

The only indented code there is the error handling. At least to me, this 
makes the code a lot more readable since there are far fewer 
combinations of conditionals.