linux-kernel - Re: [PATCH 2/2] Revert "Input: soc_button_array

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Message-ID: <4a4d577b-a085-46e8-97b9-6df27461c870@kernel.org>
Date: Wed, 25 Jun 2025 11:09:25 +0200
From: Hans de Goede <hansg@...nel.org>
To: Mario Limonciello <superm1@...nel.org>,
 Mika Westerberg <westeri@...nel.org>,
 Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 Linus Walleij <linus.walleij@...aro.org>, Bartosz Golaszewski
 <brgl@...ev.pl>, Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc: "open list:GPIO ACPI SUPPORT" <linux-gpio@...r.kernel.org>,
 "open list:GPIO ACPI SUPPORT" <linux-acpi@...r.kernel.org>,
 open list <linux-kernel@...r.kernel.org>,
 "open list:INPUT (KEYBOARD, MOUSE, JOYSTICK, TOUCHSCREEN)..."
 <linux-input@...r.kernel.org>, Mario Limonciello <mario.limonciello@....com>
Subject: Re: [PATCH 2/2] Revert "Input: soc_button_array - debounce the
 buttons"

Hi Mario,

On 24-Jun-25 10:22 PM, Mario Limonciello wrote:
> From: Mario Limonciello <mario.limonciello@....com>
> 
> commit 5c4fa2a6da7fb ("Input: soc_button_array - debounce the buttons")
> hardcoded all soc-button-array devices to use a 50ms debounce timeout
> but this doesn't work on all hardware.  The hardware I have on hand
> actually prescribes in the ASL that the timeout should be 0:
> 
> GpioInt (Edge, ActiveBoth, Exclusive, PullUp, 0x0000,
>          "\\_SB.GPIO", 0x00, ResourceConsumer, ,)
> {   // Pin list
>     0x0000
> }
> 
> Let the GPIO core program the debounce instead of hardcoding it into a
> driver.
> 
> This reverts commit 5c4fa2a6da7fbc76290d1cb54a7e35633517a522.

This is going to cause problems I'm afraid I just checked and
based on randomly checking a few DSDTs of the tablets this driver
is used on, it seems the DSDT always specifies a debounce timeout
of 0 like your example above. And on many many devices using
the soc_button_array driver debouncing is actually necessary.

May I ask what problem you are seeing with the 50ms debounce timeout /
what problem you are exactly trying to fix here ?

drivers/input/keyboard/gpio_keys.c first will call gpiod_set_debounce()
it self with the 50 ms provided by soc_button_array and if that does
not work it will fall back to software debouncing. So I don't see how
the 50 ms debounce can cause problems, other then maybe making
really really (impossible?) fast double-clicks register as a single
click .

These buttons (e.g. volume up/down) are almost always simply mechanical
switches and these definitely will need debouncing, the 0 value from
the DSDT is plainly just wrong. There is no such thing as a not bouncing
mechanical switch.

Regards,

Hans

> 
> Cc: Hans de Goede <hansg@...nel.org>
> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
> ---
>  drivers/input/misc/soc_button_array.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/input/misc/soc_button_array.c b/drivers/input/misc/soc_button_array.c
> index b8cad415c62ca..99490df42b6f2 100644
> --- a/drivers/input/misc/soc_button_array.c
> +++ b/drivers/input/misc/soc_button_array.c
> @@ -219,8 +219,6 @@ soc_button_device_create(struct platform_device *pdev,
>  		gpio_keys[n_buttons].active_low = info->active_low;
>  		gpio_keys[n_buttons].desc = info->name;
>  		gpio_keys[n_buttons].wakeup = info->wakeup;
> -		/* These devices often use cheap buttons, use 50 ms debounce */
> -		gpio_keys[n_buttons].debounce_interval = 50;
>  		n_buttons++;
>  	}
>