linux-kernel - Re: [PATCH] HID: wacom: Use ktime_t rather than int when dealing with timestamps

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Date:   Thu, 8 Jun 2023 12:51:06 +1000
From:   Peter Hutterer <peter.hutterer@...-t.net>
To:     Jason Gerecke <killertofu@...il.com>
Cc:     linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        Jiri Kosina <jikos@...nel.org>,
        Ping Cheng <pinglinux@...il.com>,
        Aaron Armstrong Skomra <skomra@...il.com>,
        Joshua Dickens <Joshua@...hua-dickens.com>,
        Jason Gerecke <jason.gerecke@...om.com>
Subject: Re: [PATCH] HID: wacom: Use ktime_t rather than int when dealing
 with timestamps

On Wed, Jun 07, 2023 at 02:41:02PM -0700, Jason Gerecke wrote:
> Code which interacts with timestamps needs to use the ktime_t type
> returned by functions like ktime_get. The int type does not offer
> enough space to store these values, and attempting to use it is a
> recipe for problems. In this particular case, overflows would occur
> when calculating/storing timestamps leading to incorrect values being
> reported to userspace. In some cases these bad timestamps cause input
> handling in userspace to appear hung.
> 
> Link: https://gitlab.freedesktop.org/libinput/libinput/-/issues/901
> Fixes: 17d793f3ed53 ("HID: wacom: insert timestamp to packed Bluetooth (BT) events")
> Signed-off-by: Jason Gerecke <jason.gerecke@...om.com>

Reviewed-by: Peter Hutterer <peter.hutterer@...-t.net>

Cheers,
  Peter

> ---
>  drivers/hid/wacom_wac.c | 4 ++--
>  drivers/hid/wacom_wac.h | 2 +-
>  2 files changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/hid/wacom_wac.c b/drivers/hid/wacom_wac.c
> index 2ccf83837134..2f16e47e4b69 100644
> --- a/drivers/hid/wacom_wac.c
> +++ b/drivers/hid/wacom_wac.c
> @@ -1314,7 +1314,7 @@ static void wacom_intuos_pro2_bt_pen(struct wacom_wac *wacom)
>  	struct input_dev *pen_input = wacom->pen_input;
>  	unsigned char *data = wacom->data;
>  	int number_of_valid_frames = 0;
> -	int time_interval = 15000000;
> +	ktime_t time_interval = 15000000;
>  	ktime_t time_packet_received = ktime_get();
>  	int i;
>  
> @@ -1359,7 +1359,7 @@ static void wacom_intuos_pro2_bt_pen(struct wacom_wac *wacom)
>  		bool range = frame[0] & 0x20;
>  		bool invert = frame[0] & 0x10;
>  		int frames_number_reversed = number_of_valid_frames - i - 1;
> -		int event_timestamp = time_packet_received - frames_number_reversed * time_interval;
> +		ktime_t event_timestamp = time_packet_received - frames_number_reversed * time_interval;
>  
>  		if (!valid)
>  			continue;
> diff --git a/drivers/hid/wacom_wac.h b/drivers/hid/wacom_wac.h
> index 1a40bb8c5810..ee21bb260f22 100644
> --- a/drivers/hid/wacom_wac.h
> +++ b/drivers/hid/wacom_wac.h
> @@ -324,7 +324,7 @@ struct hid_data {
>  	int ps_connected;
>  	bool pad_input_event_flag;
>  	unsigned short sequence_number;
> -	int time_delayed;
> +	ktime_t time_delayed;
>  };
>  
>  struct wacom_remote_data {
> -- 
> 2.41.0
>