linux-kernel - Re: [PATCH v2 10/11] HID: introduce Scan Time

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Message-ID: <20121029224331.GA15608@polaris.bitmath.org>
Date:	Mon, 29 Oct 2012 23:43:31 +0100
From:	"Henrik Rydberg" <rydberg@...omail.se>
To:	Benjamin Tissoires <benjamin.tissoires@...il.com>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Jiri Kosina <jkosina@...e.cz>,
	Stephane Chatty <chatty@...c.fr>, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 10/11] HID: introduce Scan Time

Hi Benjamin,

> Win 8 digitizer devices provides the actual scan time computed by the
> hardware itself. The value is global to the frame and is not specific
> to the multitouch protocol (though only touch, not pen, should use it
> according to the specification).
> 
> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@...il.com>
> ---
>  Documentation/input/event-codes.txt |  7 +++++++
>  drivers/hid/hid-input.c             |  4 ++++
>  drivers/hid/hid-multitouch.c        | 11 +++++++++--
>  include/linux/hid.h                 |  1 +
>  include/linux/input.h               |  1 +
>  5 files changed, 22 insertions(+), 2 deletions(-)

This is a nice feature, useful in many other contexts. As such, I
think it should be defined in the context of the input subsystem, with
a more specific definition added to the documentation. For instance,
is 100us suitable? When should it start at zero, at BTN_TOUCH? Or
should it perhaps wrap around on unsigned integer instead? Or display
the difference from the last event?

> diff --git a/Documentation/input/event-codes.txt b/Documentation/input/event-codes.txt
> index 53305bd..8f8c908 100644
> --- a/Documentation/input/event-codes.txt
> +++ b/Documentation/input/event-codes.txt
> @@ -174,6 +174,13 @@ A few EV_ABS codes have special meanings:
>      the input device may be used freely in three dimensions, consider ABS_Z
>      instead.
>  
> +* ABS_SCAN_TIME:
> +  - Used when the device provides a timestamp for each frame. The unit must be
> +    100us, and may be reset when the device don't send any events for a
> +    period of time. The values increment at each frame and thus, it can roll
> +    back to 0 when reach logical_max. If the device does not provide this
> +    information, the driver must not provide it to the user space.
> +
>  * ABS_MT_<name>:
>    - Used to describe multitouch input events. Please see
>      multi-touch-protocol.txt for details.
> diff --git a/drivers/hid/hid-input.c b/drivers/hid/hid-input.c
> index 16cc89a..5fe7bd3 100644
> --- a/drivers/hid/hid-input.c
> +++ b/drivers/hid/hid-input.c
> @@ -675,6 +675,10 @@ static void hidinput_configure_usage(struct hid_input *hidinput, struct hid_fiel
>  			map_key_clear(BTN_STYLUS2);
>  			break;
>  
> +		case 0x56: /* Scan Time */
> +			map_abs(ABS_SCAN_TIME);
> +			break;
> +

Is it not enough to map it in the case below? Or you mean this is
picked up by hid core?

>  		default:  goto unknown;
>  		}
>  		break;
> diff --git a/drivers/hid/hid-multitouch.c b/drivers/hid/hid-multitouch.c
> index c0ab1c6..21a120b 100644
> --- a/drivers/hid/hid-multitouch.c
> +++ b/drivers/hid/hid-multitouch.c
> @@ -447,12 +447,19 @@ static int mt_input_mapping(struct hid_device *hdev, struct hid_input *hi,
>  			mt_store_field(usage, td, hi);
>  			td->last_field_index = field->index;
>  			return 1;
> +		case HID_DG_SCANTIME:
> +			hid_map_usage(hi, usage, bit, max,
> +				EV_ABS, ABS_SCAN_TIME);
> +			set_abs(hi->input, ABS_SCAN_TIME, field, 0);
> +			td->last_field_index = field->index;
> +			return 1;
>  		case HID_DG_CONTACTCOUNT:
>  			td->last_field_index = field->index;
>  			return 1;
>  		case HID_DG_CONTACTMAX:
> -			/* we don't set td->last_slot_field as contactcount and
> -			 * contact max are global to the report */
> +			/* we don't set td->last_slot_field as scan time,
> +			 * contactcount and contact max are global to the
> +			 * report */
>  			td->last_field_index = field->index;
>  			return -1;
>  		case HID_DG_TOUCH:
> diff --git a/include/linux/hid.h b/include/linux/hid.h
> index 6216529..99a6418 100644
> --- a/include/linux/hid.h
> +++ b/include/linux/hid.h
> @@ -279,6 +279,7 @@ struct hid_item {
>  #define HID_DG_DEVICEINDEX	0x000d0053
>  #define HID_DG_CONTACTCOUNT	0x000d0054
>  #define HID_DG_CONTACTMAX	0x000d0055
> +#define HID_DG_SCANTIME		0x000d0056
>  
>  /*
>   * HID report types --- Ouch! HID spec says 1 2 3!
> diff --git a/include/linux/input.h b/include/linux/input.h
> index ba48743..73c3a96 100644
> --- a/include/linux/input.h
> +++ b/include/linux/input.h
> @@ -796,6 +796,7 @@ struct input_keymap_entry {
>  #define ABS_TILT_X		0x1a
>  #define ABS_TILT_Y		0x1b
>  #define ABS_TOOL_WIDTH		0x1c
> +#define ABS_SCAN_TIME		0x1d
>  
>  #define ABS_VOLUME		0x20
>  
> -- 
> 1.7.11.7
> 

Thanks,
Henrik
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