gpiolib: implement dynamic base allocation

PATCH In review Anton Vorontsov 2 participants 3 messages Mar 11, 2008 – Mar 12, 2008 GPIO

Share & tools

Anton Vorontsov

author

2008-03-11 17:41 UTC #0 lore raw

PATCH 1/3 gpiolib: implement dynamic base allocation

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).

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 <[email protected]>

---

Rebased on top of v2.6.25-rc3-mm1

 drivers/gpio/gpiolib.c |   43 ++++++++++++++++++++++++++++++++++++++-----
 1 files changed, 38 insertions(+), 5 deletions(-)

drivers/gpio/gpiolib.c +38 -5

index 623fcd9..81d81c9 100644
@@ -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... */

Signature · 1 line

1.5.2.2

David Brownell

Acked-by on v1 1/3

2008-03-11 21:11 UTC #1 lore raw

Quoted 3 lines · Anton Vorontsov

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.

Quoted 6 lines

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 <[email protected]>

Acked-by David Brownell <[email protected]>

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

Quoted 84 lines

---

Rebased on top of v2.6.25-rc3-mm1

 drivers/gpio/gpiolib.c |   43 ++++++++++++++++++++++++++++++++++++++-----
 1 files changed, 38 insertions(+), 5 deletions(-)

drivers/gpio/gpiolib.c +38 -5

index 623fcd9..81d81c9 100644
@@ -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... */

Signature · 1 line

1.5.2.2

Anton Vorontsov

author Acked-by David Brownell

2008-03-12 12:27 UTC #2 lore raw

Quoted 19 lines · David Brownell

Quoted 3 lines · Anton Vorontsov
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.
Quoted 5 lines
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.

Quoted 6 lines

Quoted 1 line
Signed-off-by Anton Vorontsov <[email protected]>
Acked-by David Brownell <[email protected]>
... 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 <[email protected]>
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.

Signed-off-by Anton Vorontsov <[email protected]>

Acked-by David Brownell <[email protected]>

---
 drivers/gpio/gpiolib.c |   43 ++++++++++++++++++++++++++++++++++++++-----
 1 files changed, 38 insertions(+), 5 deletions(-)

drivers/gpio/gpiolib.c +38 -5

index 623fcd9..81d81c9 100644
@@ -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... */

Signature · 1 line

1.5.2.2