linux-kernel - Re: [PATCH 001/001] [Input:] Propagate hardware generated event timestamp to evdev.

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 12 Jul 2013 23:44:30 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Alexander Levitskiy <sanek@...gle.com>
Cc:	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org, Rob Landley <rob@...dley.net>,
	Henrik Rydberg <rydberg@...omail.se>,
	Arve Hjønnevåg <arve@...roid.com>,
	Stephen Boyd <sboyd@...eaurora.org>
Subject: Re: [PATCH 001/001] [Input:] Propagate hardware generated event
 timestamp to evdev.

Hi Sasha,

On Wed, Jul 10, 2013 at 01:38:00PM -0700, Alexander Levitskiy wrote:
> From: Sasha Levitskiy <sanek@...gle.com>
> 
> Input: Propagate hardware event timestamp to evdev.
> 
> Convey hardware generated timestamp associated with the current event packet.
> The use of these event codes by hardware drivers is optional.
> Used to reduce jitter and improve velocity tracking in ABS_MT and other timing
> sensitive devices.
> 
> kernel v. 3.4
> 
> Signed-off-by: Sasha Levitskiy <sanek@...gle.com>
> ---
> diff --git a/Documentation/input/event-codes.txt
> b/Documentation/input/event-codes.txt
> index 53305bd..f0f0e07 100644
> --- a/Documentation/input/event-codes.txt
> +++ b/Documentation/input/event-codes.txt
> @@ -91,6 +91,15 @@ sent in the evdev event stream.
>      event and query the device (using EVIOCG* ioctls) to obtain its
>      current state.
> 
> +* SYN_TIME_SEC, SYN_TIME_NSEC:
> +  - Used to convey hardware timestamp associated with the current
> +    event packet. The use of these event codes by hardware drivers
> +    is optional. If used, the hardware driver should send the timestamp
> +    ahead of any other events associated with this packet. The timestamp
> +    should be adjusted to CLOCK_MONOTONIC base.
> +    This becomes useful for drivers of hardware that handle batching
> +    without involving the main CPU.

We already have MSC_TIMESTAMP (which is in usec), do you really need
nsec resolution?

> +
>  EV_KEY:
>  ----------
>  EV_KEY events take the form KEY_<name> or BTN_<name>. For example,
> KEY_A is used
> diff --git a/Documentation/input/multi-touch-protocol.txt
> b/Documentation/input/multi-touch-protocol.txt
> index 543101c..71af317 100644
> --- a/Documentation/input/multi-touch-protocol.txt
> +++ b/Documentation/input/multi-touch-protocol.txt
> @@ -80,6 +80,10 @@ Userspace can detect that a driver can report more
> total contacts than slots
>  by noting that the largest supported BTN_TOOL_*TAP event is larger than the
>  total number of type B slots reported in the absinfo for the ABS_MT_SLOT axis.
> 
> +Velocity tracking and temporal precision can be improved if device provides
> +exact timestamp for touches reported through SYN_TIME_SEC and SYN_TIME_NSEC.
> +The timestamp should be reported ahead of everything else in the packet.
> +
>  Protocol Example A
>  ------------------
> 
> diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
> index 41f79be..48baf6f 100644
> --- a/drivers/input/evdev.c
> +++ b/drivers/input/evdev.c
> @@ -37,6 +37,8 @@ struct evdev {
>   struct mutex mutex;
>   struct device dev;
>   bool exist;
> + int hw_ts_sec;
> + int hw_ts_nsec;
>  };
> 
>  struct evdev_client {
> @@ -109,7 +111,20 @@ static void evdev_event(struct input_handle *handle,
>   struct input_event event;
>   ktime_t time_mono, time_real;
> 
> - time_mono = ktime_get();
> + if (type == EV_SYN && code == SYN_TIME_SEC) {
> + evdev->hw_ts_sec = value;
> + return;

Why do you need this special handling? Can you simply have MSC_TIMESTAMP
to be delivered as part of the event packet and use it instead of the
event timestamp if userspace chooses to do so?

Thanks.

-- 
Dmitry
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/