linux-kernel - Re: [PATCH 1/5] gpiolib: introduce set

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Date:	Thu, 20 May 2010 11:06:00 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	felipe.balbi@...ia.com
Cc:	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Tony Lindgren <tony@...mide.com>,
	David Brownell <david-b@...bell.net>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Subject: Re: [PATCH 1/5] gpiolib: introduce set_debounce method

On Mon, 17 May 2010 13:02:30 +0300
felipe.balbi@...ia.com wrote:

> From: Felipe Balbi <felipe.balbi@...ia.com>
> 
> Few architectures, like OMAP, allow you to set
> a debouncing time for the gpio before generating
> the IRQ. Teach gpiolib about that.
> 
> ...
>
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -1447,6 +1447,49 @@ fail:
>  }
>  EXPORT_SYMBOL_GPL(gpio_direction_output);
>  
> +/**
> + * gpio_set_debounce - sets @debounce time for a @gpio
> + * @gpio: the gpio to set debounce time
> + * @debounce: debounce time is microseconds
> + */
> +int gpio_set_debounce(unsigned gpio, unsigned debounce)
> +{
> +	unsigned long		flags;
> +	struct gpio_chip	*chip;
> +	struct gpio_desc	*desc = &gpio_desc[gpio];
> +	int			status = -EINVAL;
> +
> +	spin_lock_irqsave(&gpio_lock, flags);
> +
> +	if (!gpio_is_valid(gpio))
> +		goto fail;
> +	chip = desc->chip;
> +	if (!chip || !chip->set || !chip->set_debounce)
> +		goto fail;
> +	gpio -= chip->base;
> +	if (gpio >= chip->ngpio)
> +		goto fail;
> +	status = gpio_ensure_requested(desc, gpio);
> +	if (status < 0)
> +		goto fail;
> +
> +	/* now we know the gpio is valid and chip won't vanish */
> +
> +	spin_unlock_irqrestore(&gpio_lock, flags);
> +
> +	might_sleep_if(extra_checks && chip->can_sleep);
> +
> +	return chip->set_debounce(chip, gpio, debounce);
> +
> +fail:
> +	spin_unlock_irqrestore(&gpio_lock, flags);
> +	if (status)
> +		pr_debug("%s: gpio-%d status %d\n",
> +			__func__, gpio, status);
> +
> +	return status;
> +}
> +EXPORT_SYMBOL_GPL(gpio_set_debounce);

nitlet: I suspect this function is taking gpio_lock sooner than it
strictly needs to.  Find-tuning that would decrease contention by an
insignificant amount ;)

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