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To:     linux-bluetooth@vger.kernel.org
From:   Erik Andresen <erik@vontaene.de>
Subject: HID device with multiple collections does not work
Message-ID: <319b239d-3739-63e9-9fe4-f8b4215097b2@vontaene.de>
Date:   Thu, 23 Apr 2020 19:53:20 +0200
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Hi,


I have a simple bluetooth hid device which does work in Android but not with Linux 4.19/Bluez 5. It does have two collections in its hid description:
0xA1, 0x01,        // Collection (Application)
0x85, 0x02,        //   Report ID (2)
(...)
0xC0,              // End Collection
0xA1, 0x01,        // Collection (Application)
0x85, 0x01,        //   Report ID (1)
(...)
0xC0,              // End Collection

Complete description is attached.

Since there are multiple collections I understand that every report has to be prefixed with the id, so I send
[2,0,0,0x52,0,0,0,0,0] (9 bytes) for the keycode 0x52, ID is 2.

Output from btmon is:
> ACL Data RX: Handle 3585 flags 0x02 dlen 16                                                                                                                                                                                                            #2072 [hci0] 485.047387
       ATT: Handle Value Notification (0x1b) len 11
         Handle: 0x0015
           Data: 020000520000000000

This looks good for me so far, unfortunately Linux does not pick it up, in dmesg I get:
drivers/hid/hid-core.c: undefined report_id 0 received

cat /sys/kernel/debug/hid/0005:0000:0000.000­3/events # gives me:
report (size 10) (numbered) = 00 02 00 00 52 00 00 00 00 00
so I get 10 bytes instead the 9 I send

So far I traced it to hog-lib.c, report_value_cb() of bluez where this extra 0 is prepended in the if (hog->has_report_id) block.
report->id is 0 at this point. If I skip this extra addition of the zero or manually set id=2 here it works as expected. Does someone has an idea what I do wrong or what I'm missing?

greetings,
Erik Andresen

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