| Message ID | 20210307222240.380583-3-paul@crapouillou.net (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | ec20899f1f204fa30e244cc4dc15ce34ae04126a |
| Headers | show |
| Series | [v3,1/3] input: gpio-keys: Remove extra call to input_sync | expand |
On Sun, Mar 07, 2021 at 10:22:40PM +0000, Paul Cercueil wrote: > 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 <paul@crapouillou.net> Applied with minor edits to make more use of debounce_use_hrtimer flag. Thanks.
Hi, * Dmitry Torokhov <dmitry.torokhov@gmail.com> [700101 02:00]: > On Sun, Mar 07, 2021 at 10:22:40PM +0000, Paul Cercueil wrote: > > 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 <paul@crapouillou.net> > > Applied with minor edits to make more use of debounce_use_hrtimer flag. While testing Linux next I noticed that this patch causes a null pointer dereference at least when unbinding a gpio-keys instance, see below. Regards, Tony 8< ----------------- Unable to handle kernel NULL pointer dereference at virtual address 0000000c ... PC is at hrtimer_active+0xc/0x98 LR is at hrtimer_try_to_cancel+0x24/0x140 ... [<c01c43b8>] (hrtimer_active) from [<c01c50f4>] (hrtimer_try_to_cancel+0x24/0x140) [<c01c50f4>] (hrtimer_try_to_cancel) from [<c01c5224>] (hrtimer_cancel+0x14/0x4c) [<c01c5224>] (hrtimer_cancel) from [<bf1cae24>] (gpio_keys_attr_store_helper+0x1b8/0x1d8 [gpio_keys]) [<bf1cae24>] (gpio_keys_attr_store_helper [gpio_keys]) from [<bf1cae80>] (gpio_keys_store_disabled_keys+0x18/0x24 [gpio_keys]) [<bf1cae80>] (gpio_keys_store_disabled_keys [gpio_keys]) from [<c038ec7c>] (kernfs_fop_write_iter+0x10c/0x1cc) [<c038ec7c>] (kernfs_fop_write_iter) from [<c02df858>] (vfs_write+0x2ac/0x404) [<c02df858>] (vfs_write) from [<c02dfaf4>] (ksys_write+0x64/0xdc) [<c02dfaf4>] (ksys_write) from [<c0100080>] (ret_fast_syscall+0x0/0x58)
On Tue, Apr 06, 2021 at 11:37:07AM +0300, Tony Lindgren wrote: > Hi, > > * Dmitry Torokhov <dmitry.torokhov@gmail.com> [700101 02:00]: > > On Sun, Mar 07, 2021 at 10:22:40PM +0000, Paul Cercueil wrote: > > > 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 <paul@crapouillou.net> > > > > Applied with minor edits to make more use of debounce_use_hrtimer flag. > > While testing Linux next I noticed that this patch causes a null pointer > dereference at least when unbinding a gpio-keys instance, see below. Ugh, my "minor edits" did screw things up ;( as I mixed up release and debounce timers. I'll fix it up. > > Regards, > > Tony > > 8< ----------------- > Unable to handle kernel NULL pointer dereference at virtual address 0000000c > ... > PC is at hrtimer_active+0xc/0x98 > LR is at hrtimer_try_to_cancel+0x24/0x140 > ... > [<c01c43b8>] (hrtimer_active) from [<c01c50f4>] (hrtimer_try_to_cancel+0x24/0x140) > [<c01c50f4>] (hrtimer_try_to_cancel) from [<c01c5224>] (hrtimer_cancel+0x14/0x4c) > [<c01c5224>] (hrtimer_cancel) from [<bf1cae24>] (gpio_keys_attr_store_helper+0x1b8/0x1d8 [gpio_keys]) > [<bf1cae24>] (gpio_keys_attr_store_helper [gpio_keys]) from [<bf1cae80>] (gpio_keys_store_disabled_keys+0x18/0x24 [gpio_keys]) > [<bf1cae80>] (gpio_keys_store_disabled_keys [gpio_keys]) from [<c038ec7c>] (kernfs_fop_write_iter+0x10c/0x1cc) > [<c038ec7c>] (kernfs_fop_write_iter) from [<c02df858>] (vfs_write+0x2ac/0x404) > [<c02df858>] (vfs_write) from [<c02dfaf4>] (ksys_write+0x64/0xdc) > [<c02dfaf4>] (ksys_write) from [<c0100080>] (ret_fast_syscall+0x0/0x58) >
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;
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 <paul@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(-)