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

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Date:	Wed, 12 Mar 2008 15:27:46 +0300
From:	Anton Vorontsov <avorontsov@...mvista.com>
To:	David Brownell <david-b@...bell.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] gpiolib: implement dynamic base allocation

On Tue, Mar 11, 2008 at 12:49:28PM -0800, David Brownell wrote:
> 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.

Thanks, below is the patch with updated log.

- - - -
From: Anton Vorontsov <avorontsov@...mvista.com>
Subject: gpiolib: implement dynamic base allocation

If gpio_chip->base is negative during registration, gpiolib requests
dynamic base allocation. This 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>
---
 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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