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SubjectRe: Query regarding hid-multitouch.c driver in 4.14/4.19
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Hi Benjamin,

Sorry for the delay, was waiting for the required information from our team.

On 11/13/2019 3:00 PM, Benjamin Tissoires wrote:
> Hi Neeraj,
>
> On Wed, Nov 13, 2019 at 4:11 AM Neeraj Upadhyay <neeraju@codeaurora.org> wrote:
>> Hi,
>>
>> I have one query regarding hid-multitouch.c driver and need your guidance on
>> how hid-multitouchc can restore/support the original behaviour, where, for
>> devices, for which application is not
>> HID_DG_TOUCHSCREEN/HID_DG_TOUCHPAD, and has
>> HID_DG_CONTACTID usage in its report, can still use generic input mappings.
>>
>> We are using kernel versions 4.14 , 4.19 respectively in 2 different
>> projects:
>>
>> 4.14:
>> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/drivers/hid/hid-multitouch.c?h=v4.14.153
>> 4.19:
>> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/drivers/hid/hid-multitouch.c?h=v4.19.83
>>
>> I checked the application for our hid device, it's HID_DG_PEN, device
>> also has a HID_DG_CONTACTID usage defined in
>>
>> its report.
>>
>> In 4.19, is_mt_collection is set to 'true'. All multitouch code paths or
>> input mapping is configured
>>
>> mt_allocate_report_data()
>> ...
>> for (n = 0; n < field->report_count; n++) {
>> if (field->usage[n].hid == HID_DG_CONTACTID)
>> rdata->is_mt_collection = true; //
>> is_mt_collection is set to 'true'
>> }
>> }
>>
>> mt_input_mapping()
>> ...
>> if (rdata->is_mt_collection)
>> return mt_touch_input_mapping(...) //
>> mt_touch_input_mapping() is called
>>
>> mt_event()
>> if (rdata && rdata->is_mt_collection)
>> return mt_touch_event(); // mt_touch_event() is called
>>
>> However, in 4.14, the behaviour was different, mt input mapping was done
>> only
>> for HID_DG_TOUCHSCREEN/HID_DG_TOUCHPAD , and because our hid device is
>> HID_DG_PEN, generic mappings were applied for it; with these settings,
>> device
>> responds to events.
>>
>> static int mt_input_mapping()
>> if (field->application == HID_DG_TOUCHSCREEN ||
>> field->application == HID_DG_TOUCHPAD)
>> return mt_touch_input_mapping(); // This is not called.
>>
>>
>> mt_touch_input_mapping()
>> case HID_DG_CONTACTID:
>> mt_store_field(usage, td, hi);
>> td->touches_by_report++;
>> td->mt_report_id = field->report->id; //
>> mt_report_id is not set.
>> return 1;
>>
>>
>> Looks like this behaviour changed, with below commits:
>>
>> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/drivers/hid/hid-multitouch.c?h=v4.19.83&id=8dfe14b3b47ff832cb638731f9fc696a3a84f804
>> 8dfe14b3b47f HID: multitouch: ditch mt_report_id
>> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/drivers/hid/hid-multitouch.c?h=v4.19.83&id=ba6b055e0f3b4ff4942e4ab273260affcfad9bff
>> ba6b055e0f3b HID: input: enable Totem on the Dell Canvas 27
>>
>> Can you please suggest on how we can support/preserve the original
>> behaviour?
> Hmm, I would initially say that a firmware that exports Contact ID for
> a Pen is definitely wrong. The Contact ID usage has been introduced in
> https://www.usb.org/sites/default/files/hutrr34.pdf and is
> specifically for multi-touch, not multi pen.
>
> Anyway, couple of questions:
> - does the device supports multi-pen?

Actually the device is a selfie stick device:
https://item.jd.com/33082497741.html

It does not support multi-pen.

> - can you share the report descriptor and a few events when triggering
> this particular report (ideally with hid-recorder from
> https://gitlab.freedesktop.org/libevdev/hid-tools/

Report descriptor is below:

05 0d 09 02 a1 01 85 01 09 22 a1 02 09 42 15 00 25 01 75 01 95 01 81 02
09 32 81 02 95 06 81 03 75 08 09 51 95 01 81 02 05 01 26 ff 0f 75 10 55
0e 65 33 09 30 35 00 46 b5 04 81 02 46 8a 03 09 31 81 02 c0 05 0d 09 54
95 01 75 08 81 02 85 08 09 55 25 05 b1 02 c0 05 0c 09 01 a1 01 85 02 09
e9 09 ea 0a ae 01 09 e2 09 30 15 01 25 0c 75 10 95 01 81 00 c0

Events were collected using getevent call in adb shell in android:

On 4.19

# getevent -l

add device 7: /dev/input/event6
  name:     "BLE-M1 UNKNOWN"

/dev/input/event6: EV_ABS       ABS_MT_TRACKING_ID   00000000
/dev/input/event6: EV_ABS       ABS_MT_POSITION_X    00000800
/dev/input/event6: EV_ABS       ABS_MT_POSITION_Y    00000d60
/dev/input/event6: EV_KEY       BTN_TOUCH            DOWN
/dev/input/event6: EV_SYN       SYN_REPORT           00000000
/dev/input/event6: EV_ABS       ABS_MT_TRACKING_ID   ffffffff
/dev/input/event6: EV_KEY       BTN_TOUCH            UP
/dev/input/event6: EV_SYN       SYN_REPORT           00000000
/dev/input/event6: EV_ABS       ABS_MT_TRACKING_ID   00000001
/dev/input/event6: EV_KEY       BTN_TOUCH            DOWN
/dev/input/event6: EV_SYN       SYN_REPORT           00000000
/dev/input/event6: EV_ABS       ABS_MT_TRACKING_ID   ffffffff
/dev/input/event6: EV_KEY       BTN_TOUCH            UP
/dev/input/event6: EV_SYN       SYN_REPORT           00000000

On 4.14

add device 2: /dev/input/event5
  name:     "BLE-M1 UNKNOWN"

/dev/input/event5: EV_MSC       MSC_SCAN             000d0042
/dev/input/event5: EV_KEY       BTN_TOUCH            DOWN
/dev/input/event5: EV_KEY       BTN_DIGI             DOWN
/dev/input/event5: EV_ABS       ABS_MISC             00000001
/dev/input/event5: EV_ABS       ABS_X                00000800
/dev/input/event5: EV_ABS       ABS_Y                00000d60
/dev/input/event5: EV_ABS       0029                 00000001
/dev/input/event5: EV_SYN       SYN_REPORT           00000000

/dev/input/event5: EV_MSC       MSC_SCAN             000d0042
/dev/input/event5: EV_KEY       BTN_TOUCH            UP
/dev/input/event5: EV_KEY       BTN_DIGI             UP
/dev/input/event5: EV_ABS       0029                 00000000
/dev/input/event5: EV_SYN       SYN_REPORT           00000000

/dev/input/event5: EV_MSC       MSC_SCAN             000d0042
/dev/input/event5: EV_KEY       BTN_TOUCH            DOWN
/dev/input/event5: EV_KEY       BTN_DIGI             DOWN
/dev/input/event5: EV_ABS       0029                 00000001
/dev/input/event5: EV_SYN       SYN_REPORT           00000000

/dev/input/event5: EV_MSC       MSC_SCAN             000d0042
/dev/input/event5: EV_KEY       BTN_TOUCH            UP
/dev/input/event5: EV_KEY       BTN_DIGI             UP
/dev/input/event5: EV_ABS       0029                 00000000
/dev/input/event5: EV_SYN       SYN_REPORT           00000000


As I have little understanding of the framework, use cases and of the
flow, I am sorry, if the information provided above is

incomplete (w.r.t. what you were expecting).


Thanks

Neeraj

> Cheers,
> Benjamin
>
>>
>> Thanks
>> Neeraj
>>
>> --
>> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation
>>
--
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation

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