Re: [PATCH 1/5] gpiolib: introduce set_debounce method

From: Felipe Balbi
Date: Fri May 21 2010 - 02:53:28 EST

On Fri, May 21, 2010 at 12:50:41AM +0200, ext David Brownell wrote:

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.


Not all GPIOs have hardware debounce though, so offering this
capability sort of begs the question of where/how to provide a
software debounce mechanism too...

how about adding a flag for supported features and if that hardware doesn't support we simply return, or fallback to software emulation if chosen by the user. Something like the feature flags for the i2c bus drivers.

I mean something like:

diff --git a/arch/arm/plat-omap/gpio.c b/arch/arm/plat-omap/gpio.c
index 95f92b0..ae03f6f 100644
--- a/arch/arm/plat-omap/gpio.c
+++ b/arch/arm/plat-omap/gpio.c
@@ -1855,6 +1855,7 @@ static int __init _omap_gpio_init(void)
bank->chip.get = gpio_get;
bank->chip.direction_output = gpio_output;
bank->chip.set_debounce = gpio_debounce;
+ bank->chip->flags = GPIO_FLAG_DEBOUNCE;
bank->chip.set = gpio_set;
bank->chip.to_irq = gpio_2irq;
if (bank_is_mpuio(bank)) {
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index cd85fd1..ed1ed74 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -1461,9 +1461,14 @@ int gpio_set_debounce(unsigned gpio, unsigned debounce)
spin_lock_irqsave(&gpio_lock, flags);
+ chip = desc->chip;
+ if (!(chip->flags & GPIO_FLAG_DEBOUNCE)) {
+ spin_unlock_irqrestore(&gpio_lock, flags);
+ return 0;
+ }
if (!gpio_is_valid(gpio))
goto fail;
- chip = desc->chip;
if (!chip || !chip->set || !chip->set_debounce)
goto fail;
gpio -= chip->base;
diff --git a/include/asm-generic/gpio.h b/include/asm-generic/gpio.h
index ce3eb87..26c0aa2 100644
--- a/include/asm-generic/gpio.h
+++ b/include/asm-generic/gpio.h
@@ -32,6 +32,8 @@ struct device;
struct seq_file;
struct module;
+#define GPIO_FLAG_DEBOUNCE (1 << 0)
* struct gpio_chip - abstract a GPIO controller
* @label: for diagnostics
@@ -61,6 +63,7 @@ struct module;
* names for the GPIOs in this chip. Any entry in the array
* may be NULL if there is no alias for the GPIO, however the
* array must be @ngpio entries long.
+ * @flags: a bitmap for supported features by that particular gpio chip.
* A gpio_chip can help platforms abstract various sources of GPIOs so
* they can all be accessed through a common programing interface.
@@ -104,6 +107,7 @@ struct gpio_chip {
char **names;
unsigned can_sleep:1;
unsigned exported:1;
+ unsigned flags;
extern const char *gpiochip_is_requested(struct gpio_chip *chip,

that could be used later for adding debounce emulation for chips that doesn't support hw debouncing.

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