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Message-ID: <CAN+gG=G8F3m+UUDxm0qioipyMaAFHuQzKhmqn+-2qpGUGWwk6Q@mail.gmail.com>
Date: Tue, 30 Oct 2012 11:54:20 +0100
From: Benjamin Tissoires <benjamin.tissoires@...il.com>
To: Henrik Rydberg <rydberg@...omail.se>
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
On Mon, Oct 29, 2012 at 11:43 PM, Henrik Rydberg <rydberg@...omail.se> wrote:
> 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?
Well, the thing is that I didn't wanted to copy/paste win 8 definition
for ScanTime. So I put it with my words and not in a very
understandable way :)
This allows me to forward the incoming events without having to do
anything on them...
- 100us: suitable, not sure, but it would be good to define a standard
unit for time too
- start at zero at BTN_TOUCH: no. This information allows us to do
much better false release detection. If we reset this counter, then we
will loose the time between the two touch/release. The spec says that
it is up to the device to reset it after a period of time (not
defined, but can be one second for instance). Last, BTN_TOUCH is not
reliable for hovering devices because we will still get finger
information without BTN_TOUCH.
- difference from the last event: not sure how it is implemented in
windows, but I'm not sure it's a good way of doing if the gesture
engine needs the time from the beginning of the touch...
Anyway, I would be happy to have other comments/proposals for this event code.
>
>> 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?
>
in hidinput_configure_usage, it's enough to just map it.
In hid-multitouch, We also just need to map it, and it will be handled
by hid-core in the .event callback.
Cheers,
Benjamin
>> 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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