We want to be able to report the input event as soon as the debounce
delay elapsed. However, the current code does not really ensure that,
as it uses the jiffies-based schedule_delayed_work() API. With a small
enough HZ value (HZ <= 100), this results in some input events being
lost, when a key is quickly pressed then released (on a human's time
scale).
Switching to hrtimers fixes this issue, and will work even on extremely
low HZ values (tested at HZ=24). This is however only possible if
reading the GPIO is possible without sleeping. If this condition is not
met, the previous approach of using a jiffies-based timer is taken.
Signed-off-by: Paul Cercueil <p...@crapouillou.net>
---
Notes:
v2: HRTIMER_MODE_REL_SOFT -> HRTIMER_MODE_REL
v3: Only use a hrtimer-based timer if we know that reading the GPIO
will never sleep.
drivers/input/keyboard/gpio_keys.c | 69 ++++++++++++++++++++++++------
1 file changed, 56 insertions(+), 13 deletions(-)
diff --git a/drivers/input/keyboard/gpio_keys.c
b/drivers/input/keyboard/gpio_keys.c
index 4b92f49decef..046d9dffa171 100644
--- a/drivers/input/keyboard/gpio_keys.c
+++ b/drivers/input/keyboard/gpio_keys.c
@@ -41,6 +41,7 @@ struct gpio_button_data {
unsigned int release_delay; /* in msecs, for IRQ-only buttons */
struct delayed_work work;
+ struct hrtimer debounce_timer;
unsigned int software_debounce; /* in msecs, for GPIO-driven buttons */
unsigned int irq;
@@ -49,6 +50,7 @@ struct gpio_button_data {
bool disabled;
bool key_pressed;
bool suspended;
+ bool debounce_use_hrtimer;
};
struct gpio_keys_drvdata {
@@ -144,10 +146,12 @@ static void gpio_keys_disable_button(struct
gpio_button_data *bdata)
*/
disable_irq(bdata->irq);
- if (bdata->gpiod)
- cancel_delayed_work_sync(&bdata->work);
- else
+ if (!bdata->gpiod)
hrtimer_cancel(&bdata->release_timer);
+ else if (bdata->debounce_use_hrtimer)
+ hrtimer_cancel(&bdata->debounce_timer);
+ else
+ cancel_delayed_work_sync(&bdata->work);
bdata->disabled = true;
}
@@ -361,7 +365,10 @@ static void gpio_keys_gpio_report_event(struct
gpio_button_data *bdata)
unsigned int type = button->type ?: EV_KEY;
int state;
- state = gpiod_get_value_cansleep(bdata->gpiod);
+ if (bdata->debounce_use_hrtimer)
+ state = gpiod_get_value(bdata->gpiod);
+ else
+ state = gpiod_get_value_cansleep(bdata->gpiod);
if (state < 0) {
dev_err(input->dev.parent,
"failed to get gpio state: %d\n", state);
@@ -376,11 +383,8 @@ static void gpio_keys_gpio_report_event(struct
gpio_button_data *bdata)
}
}
-static void gpio_keys_gpio_work_func(struct work_struct *work)
+static void gpio_keys_debounce_event(struct gpio_button_data *bdata)
{
- struct gpio_button_data *bdata =
- container_of(work, struct gpio_button_data, work.work);
-
gpio_keys_gpio_report_event(bdata);
input_sync(bdata->input);
@@ -388,6 +392,26 @@ static void gpio_keys_gpio_work_func(struct work_struct
*work)
pm_relax(bdata->input->dev.parent);
}
+static void gpio_keys_gpio_work_func(struct work_struct *work)
+{
+ struct gpio_button_data *bdata = container_of(work,
+ struct gpio_button_data,
+ work.work);
+
+ gpio_keys_debounce_event(bdata);
+}
+
+static enum hrtimer_restart gpio_keys_debounce_timer(struct hrtimer *t)
+{
+ struct gpio_button_data *bdata = container_of(t,
+ struct gpio_button_data,
+ debounce_timer);
+
+ gpio_keys_debounce_event(bdata);
+
+ return HRTIMER_NORESTART;
+}
+
static irqreturn_t gpio_keys_gpio_isr(int irq, void *dev_id)
{
struct gpio_button_data *bdata = dev_id;
@@ -409,9 +433,15 @@ static irqreturn_t gpio_keys_gpio_isr(int irq, void
*dev_id)
}
}
- mod_delayed_work(system_wq,
- &bdata->work,
- msecs_to_jiffies(bdata->software_debounce));
+ if (bdata->debounce_use_hrtimer) {
+ hrtimer_start(&bdata->debounce_timer,
+ ms_to_ktime(bdata->software_debounce),
+ HRTIMER_MODE_REL);
+ } else {
+ mod_delayed_work(system_wq,
+ &bdata->work,
+ msecs_to_jiffies(bdata->software_debounce));
+ }
return IRQ_HANDLED;
}
@@ -471,10 +501,12 @@ static void gpio_keys_quiesce_key(void *data)
{
struct gpio_button_data *bdata = data;
- if (bdata->gpiod)
+ if (bdata->gpiod) {
+ hrtimer_cancel(&bdata->debounce_timer);
cancel_delayed_work_sync(&bdata->work);
- else
+ } else {
hrtimer_cancel(&bdata->release_timer);
+ }
}
static int gpio_keys_setup_key(struct platform_device *pdev,
@@ -546,6 +578,13 @@ static int gpio_keys_setup_key(struct platform_device
*pdev,
if (error < 0)
bdata->software_debounce =
button->debounce_interval;
+
+ /*
+ * If reading the GPIO won't sleep, we can use a hrtimer
+ * instead of a standard timer for the software
+ * debounce, to reduce the latency as much as possible.
+ */
+ bdata->debounce_use_hrtimer =
!gpiod_cansleep(bdata->gpiod);
}
if (button->irq) {
@@ -564,6 +603,10 @@ static int gpio_keys_setup_key(struct platform_device
*pdev,
INIT_DELAYED_WORK(&bdata->work, gpio_keys_gpio_work_func);
+ hrtimer_init(&bdata->debounce_timer,
+ CLOCK_REALTIME, HRTIMER_MODE_REL);
+ bdata->debounce_timer.function = gpio_keys_debounce_timer;
+
isr = gpio_keys_gpio_isr;
irqflags = IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING;
--
2.30.1
