On Tue, Apr 06, 2021 at 11:37:07AM +0300, Tony Lindgren wrote: > Hi, > > * Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx> [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@xxxxxxxxxxxxxxx> > > > > 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) > -- Dmitry
