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Message-ID: <4990836470c5fb01babcf416ca6ccf9e5e21d152.camel@gmail.com>
Subject: (hid-logitech) Support for non-DJ receivers
From:   Filipe =?ISO-8859-1?Q?La=EDns?= <filipe.lains@gmail.com>
To:     Jiri Kosina <jikos@kernel.org>,
        Benjamin Tissoires <benjamin.tissoires@redhat.com>,
        "linux-input@vger.kernel.org" <linux-input@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Hans de Goede <hdegoede@redhat.com>
Organization: Archlinux
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Date:   Wed, 06 Jan 2021 19:07:22 +0000
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Hey,

Some of the new Logitech receivers do not have the DJ interface, this creat=
es an
issue userspace applications like libratbag, as seen in [1], because we can=
't
identify the device based on the hidraw PID.

There are two solutions for this:

1) Implement device discovery via the internal Logitech ID in libratbag and=
 all
other userspace apps.

2) Make hid-logitech-dj export a duplicated hidraw node with internal Logit=
ech
ID as PID, just like it does for the DJ interface.

In case you aren't aware of what the DJ interface is, it is essentially a
multiplexing protocol that receivers support. 6 devices could be connected =
to
the same receiver, hid-logitech-dj enables the DJ mode and the receiver wil=
l
essentially perpend the device ID to each HID report. hid-logitech-dj then
creates a HID device for each connected device and routes the HID reports t=
o the
correspondent HID device.

Option 2) would be the easier on userspace, as it keeps the same interface =
we
use for DJ receivers for other Logitech HID++ receivers and avoids all user=
space
apps to have to reimplement the same discovery logic.

Any thoughts?

[1] https://github.com/libratbag/libratbag/pull/1071

Cheers,
Filipe La=C3=ADns

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