gpiolib: introduce set_debounce method

A few architectures, like OMAP, allow you to set a debouncing time for the
gpio before generating the IRQ.  Teach gpiolib about that.

Mark said:
: This would be generally useful for embedded systems, especially where
: the interrupt concerned is a wake source.  It allows drivers to avoid
: spurious interrupts from noisy sources so if the hardware supports it
: the driver can avoid having to explicitly wait for the signal to become
: stable and software has to cope with fewer events.  We've lived without
: it for quite some time, though.

David said:
: I looked at adding debounce support to the generic GPIO calls (and thus
: gpiolib) some time back, but decided against it.  I forget why at this
: time (check list archives) but it wasn't because of lack of utility in
: certain contexts.
:
: One thing to watch out for is just how variable the hardware capabilities
: are.  Atmel GPIOs have something like a fixed number of 32K clock cycles
: for debounce, twl4030 had something odd, OMAPs were more like the Atmel
: chips but with a different clock.  In some cases debouncing had to be
: ganged, not per-GPIO.  And so forth.

Signed-off-by: Felipe Balbi <felipe.balbi@nokia.com>
Cc: Tony Lindgren <tony@atomide.com>
Cc: David Brownell <david-b@pacbell.net>
Reviewed-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 53 insertions, 0 deletions

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 362a613d266e..3ca36542e338 100644
--- 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);
 
 /* I/O calls are only valid after configuration completed; the relevant
  * "is this a valid GPIO" error checks should already have been done.
diff --git a/include/asm-generic/gpio.h b/include/asm-generic/gpio.h
index fb1ecf8baa90..4f3d75e1ad39 100644
--- a/include/asm-generic/gpio.h
+++ b/include/asm-generic/gpio.h
@@ -90,6 +90,9 @@ struct gpio_chip {
                                                 unsigned offset);
         int                     (*direction_output)(struct gpio_chip *chip,
                                                 unsigned offset, int value);
+        int                     (*set_debounce)(struct gpio_chip *chip,
+                                                unsigned offset, unsigned debounce);
+
         void                    (*set)(struct gpio_chip *chip,
                                                 unsigned offset, int value);
 
@@ -123,6 +126,8 @@ extern void gpio_free(unsigned gpio);
 extern int gpio_direction_input(unsigned gpio);
 extern int gpio_direction_output(unsigned gpio, int value);
 
+extern int gpio_set_debounce(unsigned gpio, unsigned debounce);
+
 extern int gpio_get_value_cansleep(unsigned gpio);
 extern void gpio_set_value_cansleep(unsigned gpio, int value);
 
diff --git a/include/linux/gpio.h b/include/linux/gpio.h
index 4e949a5b5b85..03f616b78cfa 100644
--- a/include/linux/gpio.h
+++ b/include/linux/gpio.h
@@ -51,6 +51,11 @@ static inline int gpio_direction_output(unsigned gpio, int value)
         return -ENOSYS;
 }
 
+static inline int gpio_set_debounce(unsigned gpio, unsigned debounce)
+{
+        return -ENOSYS;
+}
+
 static inline int gpio_get_value(unsigned gpio)
 {
         /* GPIO can never have been requested or set as {in,out}put */