3 files changed, 29 insertions, 7 deletions

diff --git a/Documentation/gpio.txt b/Documentation/gpio.txt
index 54630095aa3c..c35ca9e40d4c 100644
--- a/Documentation/gpio.txt
+++ b/Documentation/gpio.txt
@@ -107,6 +107,16 @@ type of GPIO controller, and on one particular board 80-95 with an FPGA.
 The numbers need not be contiguous; either of those platforms could also
 use numbers 2000-2063 to identify GPIOs in a bank of I2C GPIO expanders.
 
+If you want to initialize a structure with an invalid GPIO number, use
+some negative number (perhaps "-EINVAL"); that will never be valid.  To
+test if a number could reference a GPIO, you may use this predicate:
+
+        int gpio_is_valid(int number);
+
+A number that's not valid will be rejected by calls which may request
+or free GPIOs (see below).  Other numbers may also be rejected; for
+example, a number might be valid but unused on a given board.
+
 Whether a platform supports multiple GPIO controllers is currently a
 platform-specific implementation issue.
 
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index eb75d12e83b7..623fcd9b547a 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -99,7 +99,7 @@ int gpiochip_add(struct gpio_chip *chip)
          * dynamic allocation.  We don't currently support that.
          */
 
-        if (chip->base < 0 || (chip->base  + chip->ngpio) >= ARCH_NR_GPIOS) {
+        if (chip->base < 0 || !gpio_is_valid(chip->base  + chip->ngpio)) {
                 status = -EINVAL;
                 goto fail;
         }
@@ -174,7 +174,7 @@ int gpio_request(unsigned gpio, const char *label)
 
         spin_lock_irqsave(&gpio_lock, flags);
 
-        if (gpio >= ARCH_NR_GPIOS)
+        if (!gpio_is_valid(gpio))
                 goto done;
         desc = &gpio_desc[gpio];
         if (desc->chip == NULL)
@@ -209,7 +209,7 @@ void gpio_free(unsigned gpio)
         unsigned long           flags;
         struct gpio_desc        *desc;
 
-        if (gpio >= ARCH_NR_GPIOS) {
+        if (!gpio_is_valid(gpio)) {
                 WARN_ON(extra_checks);
                 return;
         }
@@ -245,7 +245,7 @@ const char *gpiochip_is_requested(struct gpio_chip *chip, unsigned offset)
 {
         unsigned gpio = chip->base + offset;
 
-        if (gpio >= ARCH_NR_GPIOS || gpio_desc[gpio].chip != chip)
+        if (!gpio_is_valid(gpio) || gpio_desc[gpio].chip != chip)
                 return NULL;
         if (test_bit(FLAG_REQUESTED, &gpio_desc[gpio].flags) == 0)
                 return NULL;
@@ -276,7 +276,7 @@ int gpio_direction_input(unsigned gpio)
 
         spin_lock_irqsave(&gpio_lock, flags);
 
-        if (gpio >= ARCH_NR_GPIOS)
+        if (!gpio_is_valid(gpio))
                 goto fail;
         chip = desc->chip;
         if (!chip || !chip->get || !chip->direction_input)
@@ -314,7 +314,7 @@ int gpio_direction_output(unsigned gpio, int value)
 
         spin_lock_irqsave(&gpio_lock, flags);
 
-        if (gpio >= ARCH_NR_GPIOS)
+        if (!gpio_is_valid(gpio))
                 goto fail;
         chip = desc->chip;
         if (!chip || !chip->set || !chip->direction_output)
@@ -531,7 +531,7 @@ static int gpiolib_show(struct seq_file *s, void *unused)
 
         /* REVISIT this isn't locked against gpio_chip removal ... */
 
-        for (gpio = 0; gpio < ARCH_NR_GPIOS; gpio++) {
+        for (gpio = 0; gpio_is_valid(gpio); gpio++) {
                 if (chip == gpio_desc[gpio].chip)
                         continue;
                 chip = gpio_desc[gpio].chip;
diff --git a/include/asm-generic/gpio.h b/include/asm-generic/gpio.h
index 7e77b6ff45bb..464c5b334dc2 100644
--- a/include/asm-generic/gpio.h
+++ b/include/asm-generic/gpio.h
@@ -16,6 +16,12 @@
 #define ARCH_NR_GPIOS           256
 #endif
 
+static inline int gpio_is_valid(int number)
+{
+        /* only some non-negative numbers are valid */
+        return ((unsigned)number) < ARCH_NR_GPIOS;
+}
+
 struct seq_file;
 struct module;
 
@@ -99,6 +105,12 @@ extern int __gpio_cansleep(unsigned gpio);
 
 #else
 
+static inline int gpio_is_valid(int number)
+{
+        /* only non-negative numbers are valid */
+        return number >= 0;
+}
+
 /* platforms that don't directly support access to GPIOs through I2C, SPI,
  * or other blocking infrastructure can use these wrappers.
  */