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Subject: Re: Query regarding hid-multitouch.c driver in 4.14/4.19
From:   Neeraj Upadhyay <neeraju@codeaurora.org>
To:     Benjamin Tissoires <benjamin.tissoires@redhat.com>
Cc:     Jiri Kosina <jikos@kernel.org>,
        Henrik Rydberg <rydberg@bitmath.org>,
        "open list:HID CORE LAYER" <linux-input@vger.kernel.org>,
        lkml <linux-kernel@vger.kernel.org>,
        linux-arm-msm@vger.kernel.org, prsood@codeaurora.org,
        gkohli@codeaurora.org
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Date:   Fri, 22 Nov 2019 04:41:59 +0000
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Hi Benjamin,

Can you please provide guidance on how to workaround this problem? Is it
possible to support the 4.14 kernel behaviour again, so that existing
clients are not impacted?


Thanks
Neeraj

On 11/14/2019 10:01 AM, Neeraj Upadhyay wrote:
> 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