linux-kernel - Re: [PATCH 1/3] gpiolib: implement dynamic base allocation

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Message-Id: <200803111349.29166.david-b@pacbell.net>
Date:	Tue, 11 Mar 2008 12:49:28 -0800
From:	David Brownell <david-b@...bell.net>
To:	Anton Vorontsov <avorontsov@...mvista.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] gpiolib: implement dynamic base allocation

On Tuesday 11 March 2008, Anton Vorontsov wrote:
> If gpio_chip->base is negative during registration, gpiolib requests
> dynamic base allocation. This is useful for devices being registered
> at run-time (in contrast to platform devices).

The issue isn't runtime or platform_device ... it's whether the
numbers are defined by the board/platform, versus on-the fly.
I2C and FPGA based expanders may be part of the board, and thus
use static assignment, for just one example.  So:

	... This dynamic allocation of GPIO numbers is useful
	for devices that aren't always present, such as GPIOs
	from expanders on add-in cards rather than mainboards.

> To avoid reusing any numbers that may have been explicitly assigned,
> but not yet registered, dynamic gpio base allocator will assign GPIO
> numbers from the biggest number on down, instead of from the smallest
> on up.
> 
> Signed-off-by: Anton Vorontsov <avorontsov@...mvista.com>

Acked-by: David Brownell <dbrownell@...rs.sourceforge.net>

... given commit comment fixup as above, since that's the only
documentation just now.

> ---
> 
> Rebased on top of v2.6.25-rc3-mm1
> 
>  drivers/gpio/gpiolib.c |   43 ++++++++++++++++++++++++++++++++++++++-----
>  1 files changed, 38 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index 623fcd9..81d81c9 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -80,6 +80,33 @@ static inline struct gpio_chip *gpio_to_chip(unsigned gpio)
>  	return gpio_desc[gpio].chip;
>  }
>  
> +static int gpiochip_find_base(int ngpio)
> +{
> +	int i;
> +	int spare = 0;
> +	int base = -ENOSPC;
> +
> +	for (i = ARCH_NR_GPIOS - 1; i >= 0 ; i--) {
> +		struct gpio_chip *chip = gpio_desc[i].chip;
> +
> +		if (!chip) {
> +			spare++;
> +			if (spare == ngpio) {
> +				base = i;
> +				break;
> +			}
> +		} else {
> +			spare = 0;
> +			i -= chip->ngpio - 1;
> +		}
> +	}
> +
> +	if (gpio_is_valid(base))
> +		pr_debug("%s: found new base at %d\n", __func__, base);
> +
> +	return base;
> +}
> +
>  /**
>   * gpiochip_add() - register a gpio_chip
>   * @chip: the chip to register, with chip->base initialized
> @@ -95,17 +122,22 @@ int gpiochip_add(struct gpio_chip *chip)
>  	int		status = 0;
>  	unsigned	id;
>  
> -	/* NOTE chip->base negative is reserved to mean a request for
> -	 * dynamic allocation.  We don't currently support that.
> -	 */
> -
> -	if (chip->base < 0 || !gpio_is_valid(chip->base  + chip->ngpio)) {
> +	if (gpio_is_valid(chip->base) &&
> +			!gpio_is_valid(chip->base  + chip->ngpio)) {
>  		status = -EINVAL;
>  		goto fail;
>  	}
>  
>  	spin_lock_irqsave(&gpio_lock, flags);
>  
> +	if (!gpio_is_valid(chip->base)) {
> +		chip->base = gpiochip_find_base(chip->ngpio);
> +		if (!gpio_is_valid(chip->base)) {
> +			status = chip->base;
> +			goto fail_unlock;
> +		}
> +	}
> +
>  	/* these GPIO numbers must not be managed by another gpio_chip */
>  	for (id = chip->base; id < chip->base + chip->ngpio; id++) {
>  		if (gpio_desc[id].chip != NULL) {
> @@ -120,6 +152,7 @@ int gpiochip_add(struct gpio_chip *chip)
>  		}
>  	}
>  
> +fail_unlock:
>  	spin_unlock_irqrestore(&gpio_lock, flags);
>  fail:
>  	/* failures here can mean systems won't boot... */
> -- 
> 1.5.2.2
> 


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